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noncryptic
2012-May-02, 10:17 AM
Under 'Dark Halo' Old Galaxies Have Many More Stars
http://www.sciencedaily.com/releases/2012/05/120501211411.htm



ScienceDaily (May 1, 2012) — Some of the oldest galaxies in the Universe have three times more stellar mass, and so many more stars, than all current models of galaxy evolution predict.

The finding comes from the Atlas3D international team, led by an Oxford University scientist, who found a way to remove the 'halo' of dark matter that has clouded previous calculations.The team's analysis means that all current models, which assumed for decades that the light we observe from a galaxy can be used to infer its stellar mass, will have to be revised.

....

The light we see from galaxies is just the tip of the iceberg, but what we really need to measure are galaxy masses that all models directly predict,' said Dr Michele Cappellari of Oxford University's Department of Physics, who led the work. 'Galaxies can contain huge numbers of small stars, planets or black holes that have lots of mass but give out very little or no light at all.'

...

kzb
2012-May-02, 11:41 AM
I can't access the full Nature paper, but I think what they are saying is that elliptical galaxies can have a stellar population peaking lower in the mass range than in spiral galaxies.

I don't think this is a completely fresh revelation. The Tully-Fisher plot remains intact for spiral galaxies.

StupendousMan
2012-May-02, 12:07 PM
This paper by Cappellari et al.,

http://arxiv.org/abs/1202.3308

states in the Abstract:


Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars. It depends on the stellar initial mass function (IMF) describing the distribution of stellar masses when the population formed. Consequently knowledge of the IMF is critical to virtually every aspect of galaxy evolution. More than half a century after the first IMF determination, no consensus has emerged on whether it is universal in different galaxies. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot be both universal, but they could not break the degeneracy between the two effects. Only recently indications were found that massive elliptical galaxies may not have the same IMF as our Milky Way. Here we report unambiguous evidence for a strong systematic variation of the IMF in early-type galaxies as a function of their stellar mass-to-light ratio, producing differences up to a factor of three in mass. This was inferred from detailed dynamical models of the two-dimensional stellar kinematics for the large Atlas3D representative sample of nearby early-type galaxies spanning two orders of magnitude in stellar mass. Our finding indicates that the IMF depends intimately on a galaxy's formation history.


If this is the paper in question, it does not imply any big change in the mainstream models of galaxies.

noncryptic
2012-May-02, 01:43 PM
Regardless, i've always found it peculiar that it is apparently thought that astronomy can see all that is there to be seen, as though there are no such things as detection threshold and noise floor.
Otoh hand i know that they know such limitations do exist, so i'm not sure what to make of it.

Cougar
2012-May-02, 02:14 PM
Regardless, i've always found it peculiar that it is apparently thought that astronomy can see all that is there to be seen, as though there are no such things as detection threshold and noise floor.

Well, I've always been amazed that they can detect a photon emitted from a hydrogen atom (http://en.wikipedia.org/wiki/H-alpha) when its electron drops from one level to another. Of course it takes a lot of such transitions for detection, but hydrogen is abundant.

Shaula
2012-May-02, 04:31 PM
Regardless, i've always found it peculiar that it is apparently thought that astronomy can see all that is there to be seen
Not thought by astronomers - they know the limits of their systems. Which is why there are so many back-up measurements, comparisons between sensing modalities, efforts at modelling and so on.

noncryptic
2012-May-02, 04:59 PM
Not thought by astronomers - they know the limits of their systems.

Yes, that's what i said.


Which is why there are so many back-up measurements, comparisons between sensing modalities, efforts at modelling and so on.

That still leaves (non-exotic) stuff that's below the threshold of detection.

And yet, apparently that which is detected is assumed to be all the normal matter that's there, and anomolous gravitional effects are explained not by as of yet undetected normal matter, but by exotic matter. I don't understand what leads to that conclusion.

TooMany
2012-May-02, 05:13 PM
This paper by Cappellari et al.,

http://arxiv.org/abs/1202.3308

If this is the paper in question, it does not imply any big change in the mainstream models of galaxies.

Did you read this in the conclusion? (my bold)



Our study convincingly demonstrates that the assumption of a universal IMF, which is still adopted in nearly every aspect of galactic
astrophysics, stellar populations and cosmology, is inconsistent with real galaxies. The results presented pose an interesting challenge to galaxy formation models, which will have to explain how stars ‘know’ what kind of galaxy they will end up inside.

kzb
2012-May-02, 05:40 PM
I thought it was long-accepted wisdom that elliptical galaxies have lower star formation rates than spirals, therefore their current average stellar mass (and luminosity) is lower (because the more massive stars have died). They must know this though.

Nereid
2012-May-02, 07:09 PM
Did you read this in the conclusion? (my bold)
StupendousMan is right: the number of published papers - in the last decade alone - exploring different IMFs and challenging or testing "the assumption of a universal IMF" is huge (one quick search I did turned up ~200, in just the last few years!).

This paper is just yet one more ... ;)

Nereid
2012-May-02, 07:14 PM
I thought it was long-accepted wisdom that elliptical galaxies have lower star formation rates than spirals, therefore their current average stellar mass (and luminosity) is lower (because the more massive stars have died). They must know this though.
Yes, of course everyone active in this sub-field knows this (as I just said, StupendousMan's comment was correct).

Here's a fun paper for you: "A Substantial Population of Low Mass Stars in Luminous Elliptical Galaxies" (arXiv:1009.5992 (http://arxiv.org/abs/1009.5992) - it ended up being published in Nature).

Reality Check
2012-May-02, 10:07 PM
And yet, apparently that which is detected is assumed to be all the normal matter that's there, and anomolous gravitional effects are explained not by as of yet undetected normal matter, but by exotic matter. I don't understand what leads to that conclusion.
The observations that leads to exotic matter are mainly the collisions of galaxy clusters. We observe a couple of big blobs of the gas in the clusters hitting each other. If the gas was entirely normal matter then we would see shockwaves and heating where the gas is. Instead we observe a sparation. IOW, the gas consists of two kinds of matter. One that is interacting electromagnetically like normal matter. Another that weakly interacts. The second kind is not normal matter.
Dark matter: Observational evidence (http://en.wikipedia.org/wiki/Dark_matter#Galaxy_clusters_and_gravitational_lens ing)

The other evidence for exotic matter is the WMAP data. Fitting models to this data reveals an upper limit to the amount of normal matter in the universe of ~4%.

TooMany
2012-May-02, 11:52 PM
Yes, of course everyone active in this sub-field knows this (as I just said, StupendousMan's comment was correct).

Here's a fun paper for you: "A Substantial Population of Low Mass Stars in Luminous Elliptical Galaxies" (arXiv:1009.5992 (http://arxiv.org/abs/1009.5992) - it ended up being published in Nature).

Both of you seem to be ignoring the fact that both papers challenge the long held theory of formation of elliptical galaxies through mergers. Wasn't that mainstream and isn't it getting harder to defend? It may also effect the way we estimate the probability of mergers which could finally put the entire merger theory of galaxy growth where it probably belongs, in the trash bin.

TooMany
2012-May-03, 12:03 AM
The observations that leads to exotic matter are mainly the collisions of galaxy clusters. We observe a couple of big blobs of the gas in the clusters hitting each other. If the gas was entirely normal matter then we would see shockwaves and heating where the gas is. Instead we observe a sparation. IOW, the gas consists of two kinds of matter. One that is interacting electromagnetically like normal matter. Another that weakly interacts. The second kind is not normal matter.
Dark matter: Observational evidence (http://en.wikipedia.org/wiki/Dark_matter#Galaxy_clusters_and_gravitational_lens ing)

The other evidence for exotic matter is the WMAP data. Fitting models to this data reveals an upper limit to the amount of normal matter in the universe of ~4%.

This discussion is off topic from this thread, but recently the Train-wreck Cluster has blurred the conclusions from the Bullet Cluster. Second, the CMB evidence is highly indirect depending on many other theoretical ideas. And finally the evidence from lack of shockwaves requires the assumption that any missing baryonic matter must be in the form of diffuse gas.

StupendousMan
2012-May-03, 01:15 AM
Both of you seem to be ignoring the fact that both papers challenge the long held theory of formation of elliptical galaxies through mergers. Wasn't that mainstream and isn't it getting harder to defend? It may also effect the way we estimate the probability of mergers which could finally put the entire merger theory of galaxy growth where it probably belongs, in the trash bin.

I give up. TooMany wins. Instead of replying to this thread, I'll just go do something productive.

Reality Check
2012-May-03, 02:53 AM
This discussion is off topic from this thread, but recently the Train-wreck Cluster has blurred the conclusions from the Bullet Cluster. Second, the CMB evidence is highly indirect depending on many other theoretical ideas. And finally the evidence from lack of shockwaves requires the assumption that any missing baryonic matter must be in the form of diffuse gas.
It is a bit off topic (maybe a new thread if you are interested?). Meanwhile:
The conclusions from the Bullet Cluster are clear - the cluster has baryonic and non-baryonic matter in it. The Train-wreck Cluster has an unexpected dark matter core without galaxies which is a puzzle which is not yet resolved.
I agree that the CMB is indirect evidence but the "many other theoretical ideas" are the LCDM model which is a strong scientific model.
The Bullet Cluster evidence (and other collision evidence) starts with the Chandra observations of X-ray emission of the heating caused by the intracluster medium (baryonic matter) in each cluster colliding. Observations in visual light showed that stars in galaxies were not greatly affected by the collision. Gravitational lensing then revealed that the majority of matter in the cluster is in 2 unheated blobs. This is assumed to be gas because there is good evidence that dark matter cannot be MACHOs (http://en.wikipedia.org/wiki/MACHO#Detection). There is also that astronomers have never detected anything but gas and isloated stars in between galaxies!

Tensor
2012-May-03, 03:53 AM
Both of you seem to be ignoring the fact that both papers challenge the long held theory of formation of elliptical galaxies through mergers. Wasn't that mainstream and isn't it getting harder to defend? It may also effect the way we estimate the probability of mergers which could finally put the entire merger theory of galaxy growth where it probably belongs, in the trash bin.

They didn't ignore it. The very next sentence after your quoted one:

A possible explanation would be for the IMF to depends on the prevailing physical conditions when the galaxy formed the bulk of their stars. Although galaxies merge hierarchically, there is growing evidence that present-day massive early-type galaxies formed most of their stars in more intense starbursts and at higher redshift than spiral galaxies.

Note that they give a possible explanation and they specifically state that galaxies merge hierarchically. So I'm not sure why you think it challenges the theory of formation by mergers.

Nereid
2012-May-03, 11:39 AM
Both of you seem to be ignoring the fact that both papers challenge the long held theory of formation of elliptical galaxies through mergers.
First, I'm not sure how accurate your summary is (you do seem to have a track record of, um, what's the word, hyperbole?).

Second, even if both papers do "challenge the long held theory of formation of elliptical galaxies through mergers", so what? Isn't that what scientists do? And aren't there dozens and dozens of papers doing much the same thing, dating back a decade or three?


Wasn't that mainstream and isn't it getting harder to defend?
This sort of sweeping generalisation isn't really helpful. But, staying in the "TooMany mode", no, and no.


It may also effect the way we estimate the probability of mergers
Um, no? :confused: Oh, I see! You meant to write "affect"! :rolleyes:

Yes, this result may well be used to make a tweak or two to various models of galaxy evolution, and so may also affect the way we estimate the probability of mergers.


which could finally put the entire merger theory of galaxy growth where it probably belongs, in the trash bin.
Perhaps not. There's rather a lot of quite independent evidence that is consistent with "the entire merger theory of galaxy growth" (whatever that is).

But why, may I ask, did you write that (you think) the theory probably belongs in the trash bin? Do you know of some alternatives (concerning galaxy evolution)? Ones that have been shown to be consistent with all the relevant evidence?

Strange
2012-May-03, 11:53 AM
Yes, that's what i said.

I'm confused. So, who does think that "astronomy can see all that is there to be seen"?


And yet, apparently that which is detected is assumed to be all the normal matter that's there, and anomolous gravitional effects are explained not by as of yet undetected normal matter, but by exotic matter. I don't understand what leads to that conclusion.

I am no expert, but at least some of the (few) articles and papers I have looked at in this area have included estimates for "normal matter that has not been detected yet". Maybe these "fudge factors" aren't large enough. But wouldn't they have to be something like a factor of 4 or 5x (rather than a "reasonable" few percent) to make dark matter unnecessary?

Cougar
2012-May-03, 01:10 PM
And yet, apparently that which is detected is assumed to be all the normal matter that's there, and anomolous gravitional effects are explained not by as of yet undetected normal matter, but by exotic matter. I don't understand what leads to that conclusion.

I think the conclusion comes from the fact that in many galaxies, you would need to find TEN TIMES as much normal matter as all the stars, gas, and dust that you can already detect. That's a lot of normal matter to hide.

TooMany
2012-May-03, 03:44 PM
I think the conclusion comes from the fact that in many galaxies, you would need to find TEN TIMES as much normal matter as all the stars, gas, and dust that you can already detect. That's a lot of normal matter to hide.

Which galaxies are those LSBs? Local dwarfs? Can you elaborate and, if convenient, site some work?

I've read papers indicating that most spirals don't even need 4X. A lot depends on the presumed distribution of unseen matter.

SagittariusAStar
2012-May-03, 04:04 PM
See Galaxies Defy Astronomers' Expectations (http://news.sciencemag.org/sciencenow/2012/04/galaxies-defy-astronomers-expectations.html).

TooMany
2012-May-03, 04:49 PM
They didn't ignore it. The very next sentence after your quoted one:


When I stated "Both of you seem to be ignoring..." I was referring to Nereid's and StupendousMan's comments, not to the paper.

The paper suggests that the composition of massive early-type galaxies shows that most of their stars formed at higher redshift than spirals and apparently under different conditions. Thus the formation of such galaxies is not likely the result of the mergers of spirals. If this is so, then probably our ideas of how common mergers are must be adjusted.

TooMany
2012-May-04, 12:33 AM
Perhaps not. There's rather a lot of quite independent evidence that is consistent with "the entire merger theory of galaxy growth" (whatever that is).


OK, I was exaggerating, maybe it's still viable. Nevertheless, the merger theory for ellipticals has been round for a very long time and now it appears most likely wrong. (Unless an elliptical will only merge with another elliptical.:rolleyes:)

Can you suggest what sort of evidence you are referring to for the merger theory? I'm aware that there is substantial evidence of mergers with halo dwarfs, going on even now. A theory that in the past there were lots and lots of dwarfs swallowed up by spirals (gradually) seems reasonable, but wholesale merger of spirals to make larger spirals seems unlikely as the means of growth, because more would be disturbed.

noncryptic
2012-May-04, 02:02 PM
I'm confused. So, who does think that "astronomy can see all that is there to be seen"?


So, who else missed the second part of what i said?

"Otoh hand i know that they know such limitations do exist"

noncryptic
2012-May-04, 02:04 PM
I think the conclusion comes from the fact that in many galaxies, you would need to find TEN TIMES as much normal matter as all the stars, gas, and dust that you can already detect. That's a lot of normal matter to hide.

To conclude that it's not there, one would also need to assume that that much normal matter can not be below the threshold of detection.

Nereid
2012-May-04, 02:06 PM
This paper by Cappellari et al.,

http://arxiv.org/abs/1202.3308

states in the Abstract:


Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars. It depends on the stellar initial mass function (IMF) describing the distribution of stellar masses when the population formed. Consequently knowledge of the IMF is critical to virtually every aspect of galaxy evolution. More than half a century after the first IMF determination, no consensus has emerged on whether it is universal in different galaxies. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot be both universal, but they could not break the degeneracy between the two effects. Only recently indications were found that massive elliptical galaxies may not have the same IMF as our Milky Way. Here we report unambiguous evidence for a strong systematic variation of the IMF in early-type galaxies as a function of their stellar mass-to-light ratio, producing differences up to a factor of three in mass. This was inferred from detailed dynamical models of the two-dimensional stellar kinematics for the large Atlas3D representative sample of nearby early-type galaxies spanning two orders of magnitude in stellar mass. Our finding indicates that the IMF depends intimately on a galaxy's formation history.


If this is the paper in question, it does not imply any big change in the mainstream models of galaxies.
See Galaxies Defy Astronomers' Expectations (http://news.sciencemag.org/sciencenow/2012/04/galaxies-defy-astronomers-expectations.html).
This popsci piece refers to same paper as the popsci piece that the OP links to; it also includes a reference to the paper I provided a link to, in post #11 (http://www.bautforum.com/showthread.php/131771-Light-is-no-basis-to-infer-stellar-mass-of-galaxies?p=2013737#post2013737) (and more).

Let's have a show of hands: who, among the BAUTians who have posted in this thread, have read "this paper by Cappellari et al." (not just the popsci pieces)?

And among those who read it, who would claim to understand it?

Nereid
2012-May-04, 02:18 PM
[...]

The paper suggests that the composition of massive early-type galaxies shows that most of their stars formed at higher redshift than spirals and apparently under different conditions.
Did you read the paper? Did you understand it?

I can't see how you drew this conclusion from the paper; would you mind explaining how please?


Thus the formation of such galaxies is not likely the result of the mergers of spirals.
How did you draw this conclusion, from your previous statement? Sorry, I can't follow your logic.


If this is so, then probably our ideas of how common mergers are must be adjusted.
How common mergers are, at least in the local universe (out to z ~ 0.25), and at least for largish galaxies, was studied using results from the original Galaxy Zoo project (just one example of 'merger studies'). Here are a couple of papers that resulted from such research: "Galaxy Zoo: the fraction of merging galaxies in the SDSS and their morphologies" (arXiv:0903.4937 (http://arxiv.org/abs/0903.4937)), and "Galaxy Zoo: The properties of merging galaxies in the nearby Universe - local environments, colours, masses, star-formation rates and AGN activity" (arXiv:0903.5057 (http://arxiv.org/abs/0903.5057)).

Nereid
2012-May-04, 02:29 PM
I think the conclusion comes from the fact that in many galaxies, you would need to find TEN TIMES as much normal matter as all the stars, gas, and dust that you can already detect. That's a lot of normal matter to hide.To conclude that it's not there, one would also need to assume that that much normal matter can not be below the threshold of detection.
No, not really.

Or, perhaps, an important caveat needs to be added, something like "with an elemental composition that is dominated by H and He" (so your statement would become something like: "To conclude that it's not there, one would also need to assume that that much normal matter, with an elemental composition that is dominated by H and He, can not be below the threshold of detection.").

Other than molecular hydrogen*, it's quite difficult to come up with hypotheses for such large masses of undetected H and He (hypotheses which are consistent with all relevant observational results); it's even more difficult to come up with hypotheses for their formation and evolution (consistent with ...).

* and, perhaps, ~km to 10^3 km balls of solid hydrogen

TooMany
2012-May-04, 03:54 PM
Did you read the paper? Did you understand it?

I can't see how you drew this conclusion from the paper; would you mind explaining how please?

"Thus the formation of such galaxies is not likely the result of the mergers of spirals."


To quote from the paper:


...there is growing evidence that present-day massive early-type galaxies formed most of their stars in more intense
starbursts and at higher redshift than spiral galaxies.


So, how could they then be the result of spiral mergers?



How did you draw this conclusion, from your previous statement? Sorry, I can't follow your logic.

"If this is so, then probably our ideas of how common mergers are must be adjusted."


It has long been thought that elliptical galaxies were the result of mergers of spirals. So the merger rate of spirals was assumed to be high enough to be consistent with that hypothesis. Hence, our assumptions about merger rates were based (in part) on that hypothesis. However, if that hypothesis has now been shown to be false, then any merger rate assumptions based on that hypothesis must be discounted.

noncryptic
2012-May-04, 07:29 PM
Other than molecular hydrogen*, it's quite difficult to come up with hypotheses for such large masses of undetected H and He (hypotheses which are consistent with all relevant observational results); it's even more difficult to come up with hypotheses for their formation and evolution (consistent with ...).

* and, perhaps, ~km to 10^3 km balls of solid hydrogen


Thanks for the constructive comment.

Let's see if i understand this.

If a significant amount of dark matter is normal matter that is hidden below detection threshold, then it must be H and He because that's what would be there unless it has been through at least one cycle of star formation, which is not very likely to be the case.

And also it must be cold and in at most fairly small condensed formations, otherwise it would already have been detected.

antoniseb
2012-May-04, 07:36 PM
... And also it must be cold and in at most fairly small condensed formations, otherwise it would already have been detected.

Right. If it is a gas, we'd detect it. If it is too massive, we'd detect it. If it is solid lumps of Hydrogen under the mass of Pluto (as a rough estimate of the limit), it might be very hard to explain how these things could have formed before the ambient temperature of the universe was above the freezing point of Hydrogen, but it would be undetectable in our local area.

ngc3314
2012-May-04, 08:42 PM
To quote from the paper:
It has long been thought that elliptical galaxies were the result of mergers of spirals. So the merger rate of spirals was assumed to be high enough to be consistent with that hypothesis. Hence, our assumptions about merger rates were based (in part) on that hypothesis. However, if that hypothesis has now been shown to be false, then any merger rate assumptions based on that hypothesis must be discounted.

As someone who has written papers addressing the merger rate of galaxies, let me rephrase that to more exactly match my reading of the last 20+ years of work on galaxy history:

"It has long been noted that some elliptical galaxies are almost certainly the result of spiral-spiral mergers, since stages in the process are evident even among nearby galaxies. Estimates of the merger rate based on the incidence and properties of such mergers, and on the change in the fraction of paired galaxies with redshift expected as some pair members merge, are broadly consistent with a large fraction of ellipticals having such an origin. The overall role of a merger origin for ellipticals depends critically on what happened at such high redshifts that extrapolations back from the present galaxy population will not be helpful and in particular mergers making the most luminous galaxies must have taken place between ellipticals because luminous-enough spirals are at best very rare."

TooMany
2012-May-04, 10:04 PM
As someone who has written papers addressing the merger rate of galaxies, let me rephrase that to more exactly match my reading of the last 20+ years of work on galaxy history:

"It has long been noted that some elliptical galaxies are almost certainly the result of spiral-spiral mergers, since stages in the process are evident even among nearby galaxies. Estimates of the merger rate based on the incidence and properties of such mergers, and on the change in the fraction of paired galaxies with redshift expected as some pair members merge, are broadly consistent with a large fraction of ellipticals having such an origin.

OK, if they are the result of spiral-spiral mergers, then are the recent findings of a large population of low mass stars (in ellipticals) consistent with that? Is it possible that the merger conditions (collision induced starbursts) result in this bottom heavy distribution while the original populations of the spirals account for a small part of the resulting stars?



The overall role of a merger origin for ellipticals depends critically on what happened at such high redshifts that extrapolations back from the present galaxy population will not be helpful and in particular mergers making the most luminous galaxies must have taken place between ellipticals because luminous-enough spirals are at best very rare."

You mean that perhaps most of the mergers occurred far enough away that we cannot observe them?

I'm trying to make sense of this from the paper:

...there is growing evidence that present-day massive early-type galaxies formed most of their stars in more intense starbursts and at higher redshift than spiral galaxies.


Are they perhaps saying that the spirals merged to form ellipticals before most spiral's stars had formed?

I'd like to read your papers about mergers so I can better understand what's going on.

TooMany
2012-May-04, 10:17 PM
Right. If it is a gas, we'd detect it. If it is too massive, we'd detect it. If it is solid lumps of Hydrogen under the mass of Pluto (as a rough estimate of the limit), it might be very hard to explain how these things could have formed before the ambient temperature of the universe was above the freezing point of Hydrogen, but it would be undetectable in our local area.

Has anyone used or proposed to use microlensing to detect the cold bodies that exist in the Oort cloud. Perhaps they are too close to us for the technique to work?

StupendousMan
2012-May-05, 01:29 AM
I'd like to read your papers about mergers so I can better understand what's going on.


Go to ADS

http://adsabs.harvard.edu/abstract_service.html

and look it up. I just did, and was given
this list of papers (http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PRE&qform=AST&arxiv_sel=astro-ph&arxiv_sel=cond-mat&arxiv_sel=cs&arxiv_sel=gr-qc&arxiv_sel=hep-ex&arxiv_sel=hep-lat&arxiv_sel=hep-ph&arxiv_sel=hep-th&arxiv_sel=math&arxiv_sel=math-ph&arxiv_sel=nlin&arxiv_sel=nucl-ex&arxiv_sel=nucl-th&arxiv_sel=physics&arxiv_sel=quant-ph&arxiv_sel=q-bio&sim_query=YES&ned_query=YES&adsobj_query=YES&aut_logic=OR&obj_logic=OR&author=^keel%0D%0A&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=&txt_logic=OR&text=&nr_to_return=200&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1)

Many of them have preprint versions which you can read freely.

Have fun!

antoniseb
2012-May-05, 12:24 PM
Has anyone used or proposed to use microlensing to detect the cold bodies that exist in the Oort cloud. Perhaps they are too close to us for the technique to work?
Proposed it? Probably not. I've done some back-of-the-envelope calculations for several ways to attempt to detect them, including occultation, and lensing, and radar or light echo... and all are way outside our ability to detect at the moment. Occultation is the closest one to feasible. In it you'd need to watch millions of background stars trying to observe drops in brightness lasting tens to hundreds of milliseconds. This would require a huge collecting surface to get enough light for the photon count per star to be fast enough to register the event... and also a different kind of detector that doesn't just bin data over long collection cycles... essentially taking 100 frames per second.

On the plus side such an observation effort would probably also turn up lots of other new science as well... details on varying stellar brightness, and what it implies. On the down side, at the rate we're increasing telescope size and detector efficiency, we're probably a century away from being able to do this.

Nereid
2012-May-05, 12:40 PM
Has anyone used or proposed to use microlensing to detect the cold bodies that exist in the Oort cloud. Perhaps they are too close to us for the technique to work?
As antoniseb said, such a project would have essentially zero chance of success with today's technology (unless the budget - both time and money - were truly astronomical :p).

However, there is an occultation project already underway, for KBOs: TAOS (http://taos.asiaa.sinica.edu.tw/).

TooMany
2012-May-05, 03:23 PM
As antoniseb said, such a project would have essentially zero chance of success with today's technology (unless the budget - both time and money - were truly astronomical :p).

However, there is an occultation project already underway, for KBOs: TAOS (http://taos.asiaa.sinica.edu.tw/).

Too bad. I suppose objects on the order of 1km in the Oort cloud are too small in angular size for such detection?

Apparently they found nothing so far and have concluded some upper limit for objects >~1km. Interesting that the HST happened to spot a 1km KBO and at an ecliptic altitude of 14 degrees which is higher than the 5 degrees of the TAOS search (90% of the search).

It wasn't really clear to me whether these finding are in conflict with theories about KBO's as a source of some comets.

slang
2012-May-05, 06:06 PM
Let's have a show of hands: who, among the BAUTians who have posted in this thread, have read "this paper by Cappellari et al." (not just the popsci pieces)?

I have.


And among those who read it, who would claim to understand it?

I don´t. Not all of it, anyway. I understand (I think) they use simulations to determine the IMF for different sized elliptical galaxies, and conclude that not all galaxies form the exact same way. What I do not understand is the work they do with the IMF. Heck, I can barely understand what sort of beast something like an `IMF´ must be. I sort of understand (I think) what the different types of IMF are like. And I think I understand broadly what the conclusions of the paper are (and I don't see it saying or suggesting that no elliptical can have spirals merging).

It's not an easy paper to read, and I did not try to follow up on the references.

TooMany
2012-May-05, 08:24 PM
..and I don't see it saying or suggesting that no elliptical can have spirals merging.


You're right, it doesn't say that but I think it suggests that most mergers would have to occur prior to the formation of most stars in the spirals.

Would anyone care to take a shot at interpreting the meaning of these statements in their conclusions?


The results presented pose an interesting challenge to galaxy formation models, which will have to explain how stars ‘know’ what kind of galaxy they will end up inside.
...
Although galaxies merge hierarchically, there is growing evidence that present-day massive early-type galaxies formed most of their stars in more intense starbursts and at higher redshift than spiral galaxies.

As I understand it, their main conclusion is the star populations of these galaxies are quite bottom heavy (more small starts than in spirals) and that their masses have been underestimated. They seem to have concluded that this is true regardless of assumptions about the form of dark matter halo.

I was hoping that ngc3314 would shed some light on the relationship to mergers.

slang
2012-May-05, 08:44 PM
You're right, it doesn't say that but I think it suggests that most mergers would have to occur prior to the formation of most stars in the spirals.

Would anyone care to take a shot at interpreting the meaning of these statements in their conclusions?

I will try.. but as my background is computer stuff, not astronomy, I welcome any corrections and/or additions from the pros! This is almost rocket science! :)


The results presented pose an interesting challenge to galaxy formation models,

I don't know enough about galaxy formation models to comment on this. Generally I see people who know about this say that galaxy formation is generally not well understood. This paper concludes that there can´t be one simple start situation to explain the evolution of the different types (or sizes) of early-type galaxies. As, AFAIK, there is no consensus on such a simple model anyway, there is no huge impact on this branch of astronomy.


which will have to explain how stars ‘know’ what kind of galaxy they will end up inside.

I think the "how stars ‘know’ [...]" remark is awkward, and don't quite understand it.


Although galaxies merge hierarchically, there is growing evidence that present-day massive early-type galaxies formed most of their stars in more intense starbursts and at higher redshift than spiral galaxies.

So most stars in massive early-type galaxies are older than (most?) current spirals we see... which might mean that this star formation happened in ellipticals as they intrinsically formed, and/or most spirals that could contribute to the ellipticals have already done so.

kzb
2012-May-08, 05:45 PM
Nereid wrote (back in post #24)

Other than molecular hydrogen*, it's quite difficult to come up with hypotheses for such large masses of undetected H and He (hypotheses which are consistent with all relevant observational results); <EDIT>

* and, perhaps, ~km to 10^3 km balls of solid hydrogen

You are a secret GHD supporter :)

TooMany
2012-May-08, 10:06 PM
Nereid wrote (back in post #24)

Other than molecular hydrogen*, it's quite difficult to come up with hypotheses for such large masses of undetected H and He (hypotheses which are consistent with all relevant observational results); <EDIT>

* and, perhaps, ~km to 10^3 km balls of solid hydrogen

You are a secret GHD supporter :)

GHD? Do you mean GHD (Garzo, Hrenya, and Dufty) granular kinetic theory? :o

What is striking to me is that we assume that only the things we can detect exist. We know about stars because they emit light. We know about gas from absorption and emission lines. We know about dust because the particles are small enough and numerous enough to absorb UV and visible and emit significant IR. Perhaps we know or think we know from MACHO surveys that there is nothing between Jupiter size hunks of matter and brown dwarfs. That leaves a range of sizes from 10^-5m to 10^7m (12 orders of magnitude in size) that are invisible objects, if they exist. Moreover cold molecular hydrogen gas is itself close to invisible.

Time will tell I guess, but I don't know how we can detect such things. Non-baryonic matter has the same problem, it just that we don't even know whether there is such a thing.

kzb
2012-May-09, 11:48 AM
TooMany wote:
GHD? Do you mean GHD (Garzo, Hrenya, and Dufty) granular kinetic theory?

I PM'd you a little while back. Please check if it got through OK. All will become clear if you read that.

What is striking to me is that we assume that only the things we can detect exist.

The whole thing IS a bit of a headache. As we were discussing on another thread, the mass budget of our galaxy disk appears to be pretty complete, at least in our locality. There does not seem to be room for much more matter, whether baryonic or not.

You probably WILL find 4% more matter, you MAY find 40%, but we need 400%. To achieve this, you have to think of some pretty unlikely hiding places.

parejkoj
2012-May-09, 08:16 PM
What is striking to me is that we assume that only the things we can detect exist. We know about stars because they emit light. We know about gas from absorption and emission lines. We know about dust because the particles are small enough and numerous enough to absorb UV and visible and emit significant IR. Perhaps we know or think we know from MACHO surveys that there is nothing between Jupiter size hunks of matter and brown dwarfs. That leaves a range of sizes from 10^-5m to 10^7m (12 orders of magnitude in size) that are invisible objects, if they exist. Moreover cold molecular hydrogen gas is itself close to invisible.


And we come back to Nereid's attempt on another thread to get you to calculate the required metallicities of the gas that such objects would have formed from, and how that squares with our understanding of the metallicity and radiation history of the Galaxy. I think you'll find that proposing enough such objects to fill in the "missing mass" results in many more problems than it might solve.

Plus, there's the Baryon Acoustic Peak in the matter distribution, the precise temperature and polarization of the CMB and the shape of its power spectrum, the history of structure formation from z~10 to z~0, etc. All of which are, independently and together, inconsistent with a baryon dominated universe.

TooMany
2012-May-10, 03:34 PM
Plus, there's the Baryon Acoustic Peak in the matter distribution, the precise temperature and polarization of the CMB and the shape of its power spectrum, the history of structure formation from z~10 to z~0, etc. All of which are, independently and together, inconsistent with a baryon dominated universe.

Why do we always have to deduce what's out there from some theory about the creation of the Universe? Forget that for a while and let's ask what can we know directly about baryonic matter without these highly theoretical conclusions. I might point out that LCDM is running into serious problems explaining what's right close by to study. Given that, why should we be so compelled by LCDM arguments?

parejkoj
2012-May-10, 04:17 PM
Why do we always have to deduce what's out there from some theory about the creation of the Universe? Forget that for a while and let's ask what can we know directly about baryonic matter without these highly theoretical conclusions.

We don't "have to", but any alternate explanation is going to have to deal with all of the above (and more). And the list I gave was not a theoretical list, but rather a list of observations that, at present, only LCDM can coherently explain.


I might point out that LCDM is running into serious problems explaining what's right close by to study.

e.g.?

TooMany
2012-May-10, 06:10 PM
TooMany: "I might point out that LCDM is running into serious problems explaining what's right close by to study."

e.g.?

Nearby:

Baryonic Tully-Fisher relation. Disk/halo conspiracy.
Lack of large numbers of dwarf galaxies.
Lack of cuspy halos predicted by the collisionless DM particles.
Dwarf galaxies with ultra-high percentages of DM, but following BTF.
Galaxies with no CDM.
Supposed stripping of CDM in dwarf galaxy mergers with MW.
Hierarchical formation of plentiful perfect-looking spiral galaxies.
Absolutely no detection of putative CDM particles.
Absence of expected CDM in our neighborhood of the Galaxy.
Lithium abundance problem.

And at broader scales:

Very large scale structures.
Cold spot in the CMB.
Incredibly massive, bright and compact galaxies at high z.
Train Wreck cluster.
Galaxy size evolution proportional to 1/(1+z).
Intercluster speeds ~1% c.
Vast flows.
Axis of evil.
Galaxies found at z~10.
Clusters at z~8.
Re-ionization epoch, where?
Evidence of little change in metallicity with z.
LCDM requires multiple assumptions of new physics - CDM, inflation, dark energy.

There are plenty of papers out there pointing out that some of the more local observations rule out the LCDM scenario anywhere from sigma 2 to 4.

Never mind that, it's the best theory we have and we're sticking with it! We really need to think outside of this box and fortunately a lot of people are.

Shaula
2012-May-10, 07:17 PM
Cold spot in the CMB.
You know that was a processing artefact, right? Pointed that out in one of the other threads on this topic.

TooMany
2012-May-10, 08:39 PM
You know that was a processing artefact, right? Pointed that out in one of the other threads on this topic.

No I didn't. Do you mind citing something. Last I heard was 1.8% chance of being a random coincidence.

Thanks.

Shaula
2012-May-10, 08:46 PM
This paper (http://arxiv.org/abs/0908.3988) shows how the spot is only found using a small class of window functions. When you use other, equally valid, windows it becomes statistically insignificant. It is a common issue in image processing - usually it is a sensor or data cleaning artefact being brought out by a basis function related to it. I am not sure they have traced its provenance, but it is still not a significant feature.

TooMany
2012-May-10, 09:31 PM
This paper (http://arxiv.org/abs/0908.3988) shows how the spot is only found using a small class of window functions. When you use other, equally valid, windows it becomes statistically insignificant. It is a common issue in image processing - usually it is a sensor or data cleaning artefact being brought out by a basis function related to it. I am not sure they have traced its provenance, but it is still not a significant feature.

I can't give you a citation off hand (maybe this (http://arxiv.org/abs/1008.3051)), but I have read some papers that specifically acknowledge that it does not show up in certain types of analysis, but it does in wavelet analysis including Spherical Mexican Hat Wavelets and those papers argued that this analysis is significant and capable of detecting features not apparently in others.

Apparently one man's evidence is another's coincidence. ;)

I'll give you this, it needs more study, but it should not be swept under the rug. There are many who take it seriously. Including those in the LCDM camp who have come up with a new thing called "cosmic texture" to explain it. A lot of what you see in papers can reflect human nature more than reality. People committed to LCDM want to make any problem go away and write papers trying to do that and vice versa.

It will be interesting to see if the Planck data can resolve the issue (or maybe just continue the controversy).

Reality Check
2012-May-11, 12:10 AM
...
Never mind that, it's the best theory we have and we're sticking with it! We really need to think outside of this box and fortunately a lot of people are.
That is correct - it is the best theory we have and we're sticking with it until a better one comes around!
Lots of people are thinking outside the box but unfortunately not coming up with models that can explain as much as the LCDM model.

LCDM includes multiple observations of actual physics - dark matter and dark energy. Inflation is backed up by observations but of course is not possible to observe.

Much of your list is not about LCDM issues, e.g. lack of large numbers of dwarf galaxies == galaxy formation models, lithium abundance problem is more to do with stellar nucleosynthesis models, etc.

parejkoj
2012-May-11, 04:21 AM
Baryonic Tully-Fisher relation. Disk/halo conspiracy.

I'm not sure this is much of a problem anymore (http://adsabs.harvard.edu/abs/2012MNRAS.420.1959C), once more complete models of the physics of ionized and neutral gas are included in the galaxy simulations.



Lack of large numbers of dwarf galaxies.


Mostly (http://adsabs.harvard.edu/abs/2007ApJ...670..313S) solved (http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1009.4505). LSST is predicted to find a large number of dwarfs that are as-yet undetectable, and more detailed simulations suggest that the number of dwarfs is fewer than initially thought. Also see the possible solution (http://www.nature.com/nature/journal/v463/n7278/full/nature08640.html) to the cuspy-cores problem (ttp://www.nature.com/nature/journal/v463/n7278/full/463167a.html).



Lack of cuspy halos predicted by the collisionless DM particles.

See above.



Dwarf galaxies with ultra-high percentages of DM, but following BTF.

citation needed?



Galaxies with no CDM.

citation needed?



Supposed stripping of CDM in dwarf galaxy mergers with MW.

I'm not sure what the problem is here. Tidal stripping of CDM is expected in any gravitational interaction with a more massive system. What am I missing?



Hierarchical formation of plentiful perfect-looking spiral galaxies.

citation needed?



Absolutely no detection of putative CDM particles.

It took about 25 years from Pauli's proposal of the neutrino to their initial direct detection. The possible search space for CDM particles is much larger than the search space for the electron neutrino. It'll be several years before this one starts to worry me.



Absence of expected CDM in our neighborhood of the Galaxy.

citation needed?



Lithium abundance problem.

This one seems to be more a problem of "which of these possible explanations is the correct one." Type lithium abundance into ADS for a wild ride of speculation. Having too many feasible solutions to chose from is not a bad place to be. Especially if you're a theorist.

As for your other list, I'm going to have to say [citation needed] for pretty much all of them. And when I say that I mean "citation for how this is a serious problem for LCDM", please.



Never mind that, it's the best theory we have and we're sticking with it! We really need to think outside of this box and fortunately a lot of people are.

Well, let me know when someone proposes something that explains just as much as the current concordance cosmology, and we'll all jump aboard. At present, there are no such models. Maybe one of the things on your list really is a serious problem, but so far most such problems have disappeared with either better data, better simulations, or both. If we've exhausted most of the search space for CDM particles in a decade or two, then I'll seriously start to worry. But that still requires an alternate proposal that handles all the same observations.

As others have said, you really don't seem to know astronomers very well. We're all kinda hoping for something to really crack here, because the repeated confirmations of LCDM are getting rather boring. If the best we can come up with is ~1-sigma deviations in our most precise surveys (e.g. Figure 20 from Anderson et al. 2012 (http://arxiv.org/abs/1203.6594)), there's not a lot of room left...

Shaula
2012-May-11, 06:08 AM
People committed to LCDM want to make any problem go away and write papers trying to do that and vice versa.
And people who dislike LCDM will grasp at any hint of deviation and trumpet it as the end of the theory.

Having read both papers I think it is safe to say I agree it needs more work. I am highly wary about only being able to use wavelets and needlets on this though. As the paper you gave rightly points out these act similarly to matched filters for gaussian signals embedded in other data. And Matched Filters are notoriously tricky things. Even attempting to assign a significance to the results of one is a bit of an art sometimes. The trouble is that the most common significance tests used have some inbuilt issues relating to data dimensionality that can lead to non-comparable results between two versions of the analysis. Essentially the effective dimensionality of the data, if reduced, can artificially increase the significance of the event. Performing multiscale wavelet analysis builds that problem right into the algorithm used and is not a problem I have ever seen cracked. Or even all that often acknowledged.

TooMany
2012-May-11, 04:13 PM
And people who dislike LCDM will grasp at any hint of deviation and trumpet it as the end of the theory.


Perhaps a bit of an exaggeration, but certainly true that they will highlight the contradictions.



Having read both papers I think it is safe to say I agree it needs more work. I am highly wary about only being able to use wavelets and needlets on this though. As the paper you gave rightly points out these act similarly to matched filters for gaussian signals embedded in other data. And Matched Filters are notoriously tricky things. Even attempting to assign a significance to the results of one is a bit of an art sometimes. The trouble is that the most common significance tests used have some inbuilt issues relating to data dimensionality that can lead to non-comparable results between two versions of the analysis. Essentially the effective dimensionality of the data, if reduced, can artificially increase the significance of the event. Performing multiscale wavelet analysis builds that problem right into the algorithm used and is not a problem I have ever seen cracked. Or even all that often acknowledged.

OK, I'm no expert on these methods of analysis, but it is what was chosen and what you see in almost every graphic presentation of the WMAP results. So if it's wrong (an illusion), doesn't throw a lot into question? We see the ubiquitous graphs showing the exact match of the data with baryonic acoustic predictions (neglecting the largest angular scales). Doesn't that data come from the same analysis?

TooMany
2012-May-11, 05:24 PM
I'm not sure this is much of a problem anymore (http://adsabs.harvard.edu/abs/2012MNRAS.420.1959C), once more complete models of the physics of ionized and neutral gas are included in the galaxy simulations...


It is true that the mainstream theorists are working hard to find ways to explain away the contradictions. Whether these explanations are sound is a matter of considerable difference of opinion. For every one of these counters, such as above, I can probably find you a paper that tends to discredit it. Take the above one that blames the lack of a cusp on SN's that clear out the center. Well maybe but I wonder how many SN's it takes. I have in fact read another paper that cast serious doubt on the viability of that proposed explanation. And how does such a proposal square with the idea that SN's are a primary creator of stars? Can you really have it both ways? One way to explain one thing and another way to explain another?


Well, let me know when someone proposes something that explains just as much as the current concordance cosmology, and we'll all jump aboard.


The point is no matter how many things some theory explains, if it is contradiction with observations it may be wrong. My point is more that we should not be jumping aboard theoretic band wagons. Theories are nice things but observations are even better. Because this theory is taken as proven by much of the community, there is some stubbornness about consideration of alternatives explanations of just about any observation.


At present, there are no such models. Maybe one of the things on your list really is a serious problem, but so far most such problems have disappeared with either better data, better simulations, or both. If we've exhausted most of the search space for CDM particles in a decade or two, then I'll seriously start to worry. But that still requires an alternate proposal that handles all the same observations.


Not everyone feels that the problems will disappear or have already been explained away.

We've already been looking for CDM for about 30 years. Recent sensitive experiments have been done with null results. Nothing too encouraging has come from LHC yet. There are people with alternative ideas that seem reasonable but they get next to no attention at all. Can't we make some progress in understanding what's around us without having to start with some grand theory of how the cosmos was created? You know, get a little humble and try to work bottom up toward an understanding rather than driving all investigation from a theory of creation.


As others have said, you really don't seem to know astronomers very well. We're all kinda hoping for something to really crack here, because the repeated confirmations of LCDM are getting rather boring. If the best we can come up with is ~1-sigma deviations in our most precise surveys (e.g. Figure 20 from Anderson et al. 2012 (http://arxiv.org/abs/1203.6594)), there's not a lot of room left...

Well, I see it differently. I see that the theory is running into problems and people are scrambling to explain them away.

Tell me something, besides a rough match with nucleosynthesis theory, what has the theory literally predicted that has been found to be true? I would claim that it has not really been predictive, it has simply been continually changed to adjust it to new findings. So is it really a theory in the sense of GR for example? I don't think it's anything like that. It's a mass of parameters and new physics (unbound by specific properties and behaviors) that is endlessly tweaked to match observations. Those matches are then announced as further evidence that the theory is correct and even called predictions. Indeed that does get boring.

Shaula
2012-May-11, 05:38 PM
Perhaps a bit of an exaggeration, but certainly true that they will highlight the contradictions.
And "People committed to LCDM want to make any problem go away and write papers trying to do that and vice versa." is not? Give me a break.


OK, I'm no expert on these methods of analysis, but it is what was chosen and what you see in almost every graphic presentation of the WMAP results. So if it's wrong (an illusion), doesn't throw a lot into question? We see the ubiquitous graphs showing the exact match of the data with baryonic acoustic predictions (neglecting the largest angular scales). Doesn't that data come from the same analysis?
No, it does not. The BAO work relies on analysis of the Fourier transforms of the data, something which requires a windowing function in order to avoid the dreaded Gibbs wiggles but which is far more analytically tractable than matched filter and similar approaches. I have been involved in doing and writing algorithms to do this kind of analysis for more than ten years - I know you dismiss me as a hopelessly close minded LCDM fanatic but ignoring the context I can safely and impartially say that these are not the same techniques at all.

parejkoj
2012-May-11, 05:43 PM
I may respond to your other comments later, but I just wanted to take this one on right now.



Tell me something, besides a rough match with nucleosynthesis theory, what has the theory literally predicted that has been found to be true?

The baryon acoustic feature in the matter correlation function/power spectrum. Not only was this a direct prediction of LCDM before its first detection by SDSS in 2005 (http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:astro-ph/0501171), but there are no other cosmological theories that produce this feature. MOND doesn't do it. TeVeS doesn't do it. Actually, neither of those is even close.

TooMany
2012-May-11, 06:20 PM
And "People committed to LCDM want to make any problem go away and write papers trying to do that and vice versa." is not? Give me a break.


No, it does not. The BAO work relies on analysis of the Fourier transforms of the data, something which requires a windowing function in order to avoid the dreaded Gibbs wiggles but which is far more analytically tractable than matched filter and similar approaches. I have been involved in doing and writing algorithms to do this kind of analysis for more than ten years - I know you dismiss me as a hopelessly close minded LCDM fanatic but ignoring the context I can safely and impartially say that these are not the same techniques at all.

You are certainly the expert this. I admit to nearly complete ignorance. What is a bit strange is that the WMAP folks published this stuff knowing that it was likely leading to false ideas? Or was that concluded later when this anomaly was discussed? Do you feel there is a general consensus that it's just an artifact? If so, how extensive are the implications on the rest of the data/conclusions?

TooMany
2012-May-11, 06:27 PM
I may respond to your other comments later, but I just wanted to take this one on right now.

The baryon acoustic feature in the matter correlation function/power spectrum. Not only was this a direct prediction of LCDM before its first detection by SDSS in 2005 (http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:astro-ph/0501171), but there are no other cosmological theories that produce this feature. MOND doesn't do it. TeVeS doesn't do it. Actually, neither of those is even close.

Going back a few years to COBE, the uniformity of the CMB was a huge surprise, not a predication, and inflation was invented to explain it. That's an example of the kind of adaption of the theory and failure to predict I"m referring to. Recently the idea of "cosmic texture" was proposed to explain the "Cold Spot". This could go on endlessly and what would it really illuminate?

Regarding MOND/TeVeS, there seems to be serious disagreement about how this or that disproves it, depending on which side of the issue you have taken.

Personally I don't like it, partly for the same reason as other things. It seems a bit concocted.

antoniseb
2012-May-11, 06:58 PM
Going back a few years to COBE, the uniformity of the CMB was a huge surprise, not a predication, and inflation was invented to explain it. ...
Now you are just talking through your hat. Inflation was proposed in Jan 1980 by Alan Guth. COBE was launched in 1989, and the results weren't known for a couple years. If you're going to argue for your position, can you please stick to arguments that leave yourself sounding credible?

parejkoj
2012-May-11, 07:13 PM
Regarding MOND/TeVeS, there seems to be serious disagreement about how this or that disproves it, depending on which side of the issue you have taken.

If you could provide a citation that suggests that any of the modified gravity models can produce the BAO feature in the matter correlation function or power spectrum without resorting to dark matter, I'd love to see it. This problem with MOND has been known for quite a while. If you don't understand what I mean by the BAO, you can ask.

As it is, you seem to be trying to play a "he said, she said" game with people who know the relevant literature. Unless you provide citations to relevant papers, there's not much point in arguing. This goes along with antoniseb's comment about your hyperbole regarding inflation; I think you've been trying to learn too much astronomy via press release.

Shaula
2012-May-11, 07:51 PM
You are certainly the expert this. I admit to nearly complete ignorance. What is a bit strange is that the WMAP folks published this stuff knowing that it was likely leading to false ideas? Or was that concluded later when this anomaly was discussed? Do you feel there is a general consensus that it's just an artifact? If so, how extensive are the implications on the rest of the data/conclusions?
Not an expert - an informed user! Most people applying signal processing techniques, frankly, click the button and accept the results. 9/10 times that is a safe thing to do - the algorithms are usually well behaved. The trouble comes when you hit the one time in ten that a data artefact is an equally valid explanation for what you see. Wavelets and their ilk are pretty complex in the way they interact with data and usually people don't fully understand them. It is rather like applying statistical tests to data. A lot of papers still use significance statistics based on a gaussian assumption without checking how valid this assumption is.

It is usually true that physicists are at best mediocre statisticians. I am 'lucky' in that I have statisticians for friends who never let me forget that. Papers often get through peer review without a full review of the statistical techniques used. Less common in particle physics papers but quite common in astrophysics papers. Does this invalidate all the results out there? No. But it does mean that blindly quoting papers can get you in to trouble.

Short version: Statistics are tricky things. This confusion most directly affects any papers claiming to have found an anomalous feature in the background. It is all about how you drive down the background reliably to find one anomalous patch. Papers looking at larger, periodic patterns are going to be safer from this sort of issue because they tend to ignore single occurrence anomalies (to an extent). So the BAO work is safe.

However I do not think that the matter is closed. For now the most likely answer is artefact. What is not clear is where this artefact came from. If it is actually in the data then it is not the same as a cold spot but it is still a significant deviation from the background pattern. So I would say it is not evidence you can use against the LCDM model yet - but equally it is not explained away and cannot be discounted as uninteresting.

TooMany
2012-May-11, 08:58 PM
Now you are just talking through your hat. Inflation was proposed in Jan 1980 by Alan Guth. COBE was launched in 1989, and the results weren't known for a couple years. If you're going to argue for your position, can you please stick to arguments that leave yourself sounding credible?

I've got the history wrong. Reading a brief account, it appears that the theory was actually motivated by the magnetic monopole problem.

"Guth was to find that the decay of the false vacuum at the beginning of the universe would produce amazing results, namely the exponential expansion of space." Thus somehow diluting the monopoles sufficiently to make them unlikely to be detected.

Then there was also the flatness problem. Omega = 1 exactly. So apparently he had a solution for that too.

According to what I read, shortly after formulating this theory (weeks), he was told that the CMB was very uniform, too uniform to explain (long before COBE, as you pointed out). But bingo, inflation explains that too and we've killed three fatal BBT problems with one stone!

What is the physical basis for inflation? Is it directly predicted from GR and QM and the standard model of particles? Or is it just a conjecture created to solve a problem that already existed with BBT thirty years ago? I know now that it is taken for granted as fact by most cosmologists. However, I don't believe that it is based on any known physics, so you cannot make any precise predictions about inflation. Instead you just assume it occurred and then you juggle your inflation parameters until they match some observations and then declare that it is correct.

With this theory we now invoke an expansion by a factor of 10^74 that happen during a time period (< 10^-33 s) many orders of magnitude smaller than the time that light requires to traverse the length of a proton. (A realm that seems way beyond any knowledge we currently have of physical law or that we can even hope to experiment with.)

That is the point that I was trying to make, although I was quite incorrect in the way I specifically described it. You can consider this a theory, but it is not at all in the same sense as GR or thermodynamics and the like. Currently theorist are also adjusting the properties of CDM to make things come out right. Maybe if we get the right mix of hot, cold, warm and just the right degree of interaction with that stuff we can get it to explain things and then once again declare it firmly part of this theory.

How can I prove that inflation never happened? That's a tough one. Like proving that undetectable particles don't exist.

TooMany
2012-May-11, 09:13 PM
Not an expert - an informed user! Most people applying signal processing techniques, frankly, click the button and accept the results. 9/10 times that is a safe thing to do - the algorithms are usually well behaved. The trouble comes when you hit the one time in ten that a data artefact is an equally valid explanation for what you see. Wavelets and their ilk are pretty complex in the way they interact with data and usually people don't fully understand them. It is rather like applying statistical tests to data. A lot of papers still use significance statistics based on a gaussian assumption without checking how valid this assumption is.

It is usually true that physicists are at best mediocre statisticians. I am 'lucky' in that I have statisticians for friends who never let me forget that. Papers often get through peer review without a full review of the statistical techniques used. Less common in particle physics papers but quite common in astrophysics papers. Does this invalidate all the results out there? No. But it does mean that blindly quoting papers can get you in to trouble.

Short version: Statistics are tricky things. This confusion most directly affects any papers claiming to have found an anomalous feature in the background. It is all about how you drive down the background reliably to find one anomalous patch. Papers looking at larger, periodic patterns are going to be safer from this sort of issue because they tend to ignore single occurrence anomalies (to an extent). So the BAO work is safe.

However I do not think that the matter is closed. For now the most likely answer is artefact. What is not clear is where this artefact came from. If it is actually in the data then it is not the same as a cold spot but it is still a significant deviation from the background pattern. So I would say it is not evidence you can use against the LCDM model yet - but equally it is not explained away and cannot be discounted as uninteresting.

Fair enough. I don't know much about image processing mathematics, but I am somewhat familiar with the sorts of artifacts that can result from JPEG compression which may be analogous. But those tend to be more or less ubiquitous rather than singular.

I agree with your concerns about statistics. They have become the central theme in many papers, so they better get it right. You know the old joke, "there are damn lies and then there's statistics."

Outsiders like myself can get a little uncomfortable when we are told that "everything matches our predictions perfectly, but please ignore that big dark spot; it's just an anomaly".

Anyway, thanks for the info and one more question: Do you think that Planck data will in any way help to resolve the issue?

antoniseb
2012-May-11, 09:27 PM
... What is the physical basis for inflation? Is it directly predicted from GR and QM and the standard model of particles? Or is it just a conjecture created to solve a problem that already existed with BBT thirty years ago?...

Without getting too involved in String Theory ideas, you can't really say much about what caused inflation... and it is certainly valid to look for alternatives that explain what it explains. Really, at this point, the direction of science of inflation is to quantify what we are seeing well enough that it can eventually give us the framework for some more elegant theory.

One of the things that you've been saying or alluding to in you many posts, is that the Big Bang, and Inflation, and Dark Matter, and Dark Energy are not theories which have some first principles the way General Relativity does. GR is testable (and will eventually need to be superseded by something that can also be compatible with QM). It is so elegant... that it has pretty much spoiled it for you. Nothing less elegant seems right to you, and lets be pragmatic, LCDM is a model and framework for increasing the quality of our measurements, and for giving context to observations.

This whole thing (BBT, GR, DM, DE, etc) is the state of things as we see them today. Some people dismiss it all as "epicycles", by which they (hopefully) mean that we are making measurements that get us to a model that predicts and explains what we see to within the limit of our ability to measure, using tools we know how to use (epicycles were a mathematical technique to make very good predictions of the positions of the planets). Copernicus made an innovation which reduced the number of epicycles from 86 to 43... He was still working with circular motions superimposed on each other. That change came from working with the refined observational data of himself and his predecessors... and then 65 years later, Kepler went one step further, and found the ellipses, and epicycles got their bad name... and then a century and a half later Newton gave some reasonable explanation for Kepler's laws.

So I suspect that you are mostly complaining that we aren't at the equivalent of Newton's place in this parallel to planetary theory... we are still working out the details of how things work and move and more. But let's point out that like the Planetary Theorists, we are right now working (as always) at the very limits of what our technology will let us see, but now the problem we are looking at is something that is intertwined both at the largest possible scale and the smallest, and our ability to have many people working together and in parallel on scientific endeavors is far beyond anything from Copernicus' time.

We know we are working with models, and make no claim that the ultimate truth of these things is known. We are on the hunt for that truth... and we have a pretty good sense of what we know and don't know. We'd be happier with your complaints if you'd listen when we answer them, and maybe read the papers we point you to.

Shaula
2012-May-11, 09:35 PM
Anyway, thanks for the info and one more question: Do you think that Planck data will in any way help to resolve the issue?
It may do. It will certainly give us more more data points and allow us to better understand the structure (if it is there in both sets of data) that has caused this. But to be honest more would be got out of a rigorous statistical review of the processing done on the WMAP data. I suspect that what is happening is that people downstream of the pre-processors are perhaps not as familiar with the data conditioning that has already happened, or are perhaps not as conversant with the signal processing that they are doing as they could be. It should be a reminder to anyone who deals with data like this that they need to be careful, methodical and precise in what they do. Maybe I am being unfair on the researchers who first found this but I would personally never trust one filter from my toolbox.

TooMany
2012-May-11, 10:39 PM
If you could provide a citation that suggests that any of the modified gravity models can produce the BAO feature in the matter correlation function or power spectrum without resorting to dark matter, I'd love to see it. This problem with MOND has been known for quite a while. If you don't understand what I mean by the BAO, you can ask.


My grasp of baryonic acoustic oscillations is pretty vague, but I believe these are supposed to be results of collapsing areas of matter that bounce back leaving voids with mostly CDM left behind? (You can laugh now.)

I'm not an advocate of MOND. Perhaps other tests for MOND can be found and dispense with it. It's a theory about gravity, not the CMB. I'm reluctant to take the CMB as first order evidence of much of anything (at this point). You see big conclusions drawn from its ever so subtle texture. To test MOND we need something more direct.


As it is, you seem to be trying to play a "he said, she said" game with people who know the relevant literature. Unless you provide citations to relevant papers, there's not much point in arguing. This goes along with antoniseb's comment about your hyperbole regarding inflation; I think you've been trying to learn too much astronomy via press release.

How do I know which papers I should believe and which I should not believe? That's not an easy thing for a beginner. There are plenty of contradictions out there. No sooner than one is published another contradicts it.

I admit to getting leads from the popular press, but I take their interpretation of what was published with a grain of salt and go find the paper they are talking about for starters. I do not take press releases at face value. If I'm interested I look for more papers; not that I fully understand them, but I can read what the writers are actually concluding and more or less understand the methodology.

There is some diversity of opinion about current LCDM, it's not seen as a slam dunk by everyone.

TooMany
2012-May-11, 11:24 PM
Without getting too involved in String Theory ideas, you can't really say much about what caused inflation... and it is certainly valid to look for alternatives that explain what it explains. Really, at this point, the direction of science of inflation is to quantify what we are seeing well enough that it can eventually give us the framework for some more elegant theory.

One of the things that you've been saying or alluding to in you many posts, is that the Big Bang, and Inflation, and Dark Matter, and Dark Energy are not theories which have some first principles the way General Relativity does. GR is testable (and will eventually need to be superseded by something that can also be compatible with QM). It is so elegant... that it has pretty much spoiled it for you. Nothing less elegant seems right to you, and lets be pragmatic, LCDM is a model and framework for increasing the quality of our measurements, and for giving context to observations.

This whole thing (BBT, GR, DM, DE, etc) is the state of things as we see them today. Some people dismiss it all as "epicycles", by which they (hopefully) mean that we are making measurements that get us to a model that predicts and explains what we see to within the limit of our ability to measure, using tools we know how to use (epicycles were a mathematical technique to make very good predictions of the positions of the planets). Copernicus made an innovation which reduced the number of epicycles from 86 to 43... He was still working with circular motions superimposed on each other. That change came from working with the refined observational data of himself and his predecessors... and then 65 years later, Kepler went one step further, and found the ellipses, and epicycles got their bad name... and then a century and a half later Newton gave some reasonable explanation for Kepler's laws.

So I suspect that you are mostly complaining that we aren't at the equivalent of Newton's place in this parallel to planetary theory... we are still working out the details of how things work and move and more. But let's point out that like the Planetary Theorists, we are right now working (as always) at the very limits of what our technology will let us see, but now the problem we are looking at is something that is intertwined both at the largest possible scale and the smallest, and our ability to have many people working together and in parallel on scientific endeavors is far beyond anything from Copernicus' time.

We know we are working with models, and make no claim that the ultimate truth of these things is known. We are on the hunt for that truth... and we have a pretty good sense of what we know and don't know. We'd be happier with your complaints if you'd listen when we answer them, and maybe read the papers we point you to.

OK, agreed. That's exactly what I'm trying to say about this theory. I would not dismiss it, but I would not assume it's truth either and apply it without doubt in all analysis of observations. In other words, even though the theory is very tempting, doctrines and dogma can be bad for science. Particularly because in this case, the theory in part dictates the interpretation of the observations!

An example of this concern comes in fusion research where almost all the eggs are in one basket, ITER. Other approaches are so underfunded as to approach starvation. The ITER direction has become doctrine in the fusion physics community. It absorbs billions while a paltry few million are left for other innovative paths. I'm sure some career physicist in that community would say something like: "Well it is the best way we know right now so it should continue to absorb most of the available funding". There are some reasons to doubt that ITER, even if it "works", will ever be practical.

Hopefully the same thing is not going on in astronomy with LCDM projects sucking up all the research funds available. I've heard complaints (in papers and news articles) from other astronomers about this. But it's not just funds. It's group think that creates a bias against innovation. E.g., "well I have new idea and I'd like to check it out." "Do you realize that that is impossible in well-established theory? I cannot support you in such a pursuit."


We'd be happier with your complaints if you'd listen when we answer them, and maybe read the papers we point you to.

Why do you assume that I do not? I do check into these things. Sometimes the papers are massive and the point that the OP is trying to make is hard to extract. Also, I peruse enough papers to know that the ones often suggested are in disagreement with others. They are often attempts at explaining divergence from theory by considering some other effect to reduce the strain. They are not always very compelling.

parejkoj
2012-May-11, 11:32 PM
My grasp of baryonic acoustic oscillations is pretty vague, but I believe these are supposed to be results of collapsing areas of matter that bounce back leaving voids with mostly CDM left behind? (You can laugh now.)

I'm not an advocate of MOND. Perhaps other tests for MOND can be found and dispense with it. It's a theory about gravity, not the CMB. I'm reluctant to take the CMB as first order evidence of much of anything (at this point). You see big conclusions drawn from its ever so subtle texture. To test MOND we need something more direct.

I'm not talking about the CMB, I'm talking about the matter distribution as traced by galaxies. It's a pretty direct measurement: look for a peak in the galaxy/galaxy correlation function around the 150Mpc scale. And as I said, it was a prediction of LCDM before it was discovered, and no other cosmological theory produces it. As a direct prediction of LCDM, it can be used as a standard ruler to measure the angular diameter distance instead of the luminosity distance of, e.g. supernova searches. The position and amplitude of the peak provides quite strong constraints on the cosmological parameters that are orthogonal to those produced by supernova or CMB measurements.

I've given you two references for the measurement of the BAO feature so far (Eisenstein et al. 2005 (http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:astro-ph/0501171) and Anderson et al. 2012 (http://arxiv.org/abs/1203.6594), which is currently under review); maybe you could read them? If you have trouble with those, the wikipedia page (http://en.wikipedia.org/wiki/Baryon_acoustic_oscillations=) is quite good, as is this page by Martin White (http://astro.berkeley.edu/~mwhite/bao/) and these various links from Daniel Eisenstein (https://www.cfa.harvard.edu/~deisenst/acousticpeak/), particularly the animations of expanding waves in the 5th bullet and this description (http://www.cfa.harvard.edu/~deisenst/acousticpeak/acoustic_physics.html).

Also, why are you so quick to reject measurements of the CMB? It's the most perfect blackbody ever observed. We've measured its power spectrum on scales from the whole sky down to below an arcminute at quite astonishing accuracy, and we have a single coherent explanation for the exact amplitude and position of all the peaks in said power spectrum, including the effects of non-linear matter evolution in the universe (gravitational lensing from galaxies and clusters, scattering from hot gas, the Sunyaev-Zeldovich effect, etc.) on the smallest scales.

Focusing on the lowest multipole is kinda like claiming that because 1998 was the warmest year on record in the CRU data, global warming isn't happening. What about the hundreds of other multipoles that have been measured by a dozen or so different surveys? The lowest multipoles are the ones that are most uncertain, because of the windowing effects that Shaula described and because of the effects of non-CMB sources (e.g., the Galaxy!) that are very hard to remove on those scales.


How do I know which papers I should I believe and which I should not believe? That's not an easy thing for a beginner. There are plenty of contradictions out there. No sooner than one is published another contradicts it.

I wonder where you've gotten this idea about "plenty of contradictions?" If you have papers that you are curious about or that you'd like to understand better, you could start a thread about them here on BAUT. But coming in with the view that "astronomers are doing everything wrong" doesn't really endear you to those who might be best placed to answer your questions.

TooMany
2012-May-12, 12:19 AM
I wonder where you've gotten this idea about "plenty of contradictions?" If you have papers that you are curious about or that you'd like to understand better, you could start a thread about them here on BAUT. But coming in with the view that "astronomers are doing everything wrong" doesn't really endear you to those who might be best placed to answer your questions.

I never claimed "astronomers are doing everything wrong". One example of contradictions is in relation to the "cold spot". There were a couple of papers concluding that there was a dearth of galaxies (a large void) way out there. Later there were papers denying these findings and taking issue with the statistical methods used. Out of curiosity I wondered if the authors of one original paper were properly chastened but apparently they were not. I'll put your links in my reading queue and thanks for them. There's an awful lot to absorb. :)

TooMany
2012-May-12, 04:12 PM
If you have trouble with those, the wikipedia page (http://en.wikipedia.org/wiki/Baryon_acoustic_oscillations=) is quite good, as is this page by Martin White (http://astro.berkeley.edu/~mwhite/bao/) and these various links from Daniel Eisenstein (https://www.cfa.harvard.edu/~deisenst/acousticpeak/), particularly the animations of expanding waves in the 5th bullet and this description (http://www.cfa.harvard.edu/~deisenst/acousticpeak/acoustic_physics.html).


All right, the beginners version in the wiki has gotten me started and it raises an immediate question that maybe you can answer. The shells of concentrated matter created by the acoustic process also entail an under-density of CDM where clusters are now and an over-density in voids. This means the total CDM component is even higher than that derived for clusters. In addition, it implies that voids are massive with CDM since it accounts for at least 80% of all mass overall. We know voids have very few galaxies and thus presumably little baryonic matter. There should be evidence of the extra mass in voids. In fact, most of the mass in the universe should be in the voids. This extra mass would also tend to decrease the expansion rate of voids below the average rate.

Has all of this been born out in measurements? I just starting here so I have no idea.

parejkoj
2012-May-12, 08:21 PM
The shells of concentrated matter created by the acoustic process also entail an under-density of CDM where clusters are now and an over-density in voids. This means the total CDM component is even higher than that derived for clusters. In addition, it implies that voids are massive with CDM since it accounts for at least 80% of all mass overall. We know voids have very few galaxies and thus presumably little baryonic matter. There should be evidence of the extra mass in voids. In fact, most of the mass in the universe should be in the voids. This extra mass would also tend to decrease the expansion rate of voids below the average rate.


Be careful: the BAO is completely separate from the existence of voids and walls. Voids and walls would form in a 100% dark matter universe, with no baryons or neutrinos or photons. The BAO only occurs in a universe with baryons and dark matter. I like to call it "proof that there are baryons in the Universe!" ;)

The BAO is on a scale much larger (~150 Mpc) than the voids (~10-20 Mpc in diameter). The BAO appears because dark matter falls onto the initial baryon overdensity at that large scale, so if there are no baryons somewhere, then there's nothing for the dark matter to be attracted to. It is also a fluctuation of order a few percent above the mean overdensity at that scale, and can only be discovered with a large volume galaxy correlation function/power spectrum survey.

TooMany
2012-May-12, 10:12 PM
Be careful: the BAO is completely separate from the existence of voids and walls. Voids and walls would form in a 100% dark matter universe, with no baryons or neutrinos or photons. The BAO only occurs in a universe with baryons and dark matter. I like to call it "proof that there are baryons in the Universe!" ;)

The BAO is on a scale much larger (~150 Mpc) than the voids (~10-20 Mpc in diameter). The BAO appears because dark matter falls onto the initial baryon overdensity at that large scale, so if there are no baryons somewhere, then there's nothing for the dark matter to be attracted to. It is also a fluctuation of order a few percent above the mean overdensity at that scale, and can only be discovered with a large volume galaxy correlation function/power spectrum survey.

OK, I was all excited that they could account for the texture of the voids and their formation, but it has nothing to do with that. You are saying this is a much more subtle over/under density, on the order of a few percent? That scale is just 10 times the extreme baryonic density fluctuations that are seen in the SDSS data. This must be some highly statistical argument that such a thing exists, because the substructure on that scale is so coarse.

I read that this BAO size at recombination is the same as the size now, ~150 Mpc. How can that be if the universe has expanded at lot since then? How far do you think baryons can fall toward a few percent over-density during 13.4 Gy? I'd better read some more. (A 20 Mpc void could barely be cleared even with matter moving at steadily at 1,000km/s in the lifetime of the universe. How do we account for them?)

antoniseb
2012-May-12, 10:39 PM
... How do we account for them? ...

This has gotten pretty off topic... I don't blame anyone, but I *do* suggest starting a new thread if you want to talk about the creation of voids and walls. Otherwise, this discussion will get lost.

Nereid
2012-May-22, 03:39 AM
I never claimed "astronomers are doing everything wrong".
I know antoniseb has suggested that I not write a post like this (well, he implied it, and it's good advice anyway), but ...

... perhaps you think you didn't; perhaps you actually didn't, in some strict sense.

However, you certainly have - or have had - a habit of very strongly implying that astronomers, in general, are closed-minded, bent on defending widely accepted models and theories (to the exclusion of alternatives), and do not regard observation as primary.

Worse, when various BAUTians put time and effort into trying to answer the actual content/question parts of your (often quite wild) statements, my impression is that you rarely bother to follow up in sufficient detail (when those answers involve, in effect, a demolition of what you seem to have hoped to find).

You've probably noticed that some BAUTians have ceased responding to posts you've written, and that some of those might - just might! - actually be quite well-informed about the topics you seem so interested in. Perhaps you might ponder on why that is.


One example of contradictions is in relation to the "cold spot". There were a couple of papers concluding that there was a dearth of galaxies (a large void) way out there. Later there were papers denying these findings and taking issue with the statistical methods used. Out of curiosity I wondered if the authors of one original paper were properly chastened but apparently they were not.
Chastened? Chastened?!? :confused:

I'll try one last time: you really, really should make a strong effort to get to know some real astronomers. You know, the people who've spent decades doing astronomy, and (in many cases) nothing but astronomy their entire adult lives (they probably even dream astronomy!), and much of their pre-adult lives too.


I'll put your links in my reading queue and thanks for them. There's an awful lot to absorb. :)
Yes, there is. And there are lots of people here who'd be only to happy to help you absorb, and learn.

Shaula
2012-May-22, 05:17 AM
Chastened? Chastened?!?
Using that term implies, to me, a poor understanding of what a paper is and what it means. Science generally is a rather complicated topic. The arguments against the cold spot were quite subtle, a mix of signal processing and statistics. The background to it was probably outside the experience of the people producing the paper, just like precision astrophysics may outside the experience of the people who wrote the counter-paper. No one can be an expert on everything.

The goal of a paper is not to lay out the truth but to present findings, findings people can then assess and respond to in the hope that the community of scientists as a whole can bring along their collective skills/knowledge and either support or refute the work. Dozens of papers and analyses later and you might have something that has run the gauntlet, been tested and is accepted. Which is why it is usually so pointless throwing arxiv quotes at each other.

People seem to want to know the latest and best ideas too much now. They skip the whole 'letting the community test it' phase and then complain that 'science' cannot make up its mind! It is rather like claiming a business is headless because it doesn't follow through on every bid proposal its R&D department put forwards.

noncryptic
2012-May-22, 12:23 PM
> Chastened? Chastened?!?

Using that term implies, to me, a poor understanding of what a paper is and what it means.

It also implies a poor understanding of how science works.
Science is not so much about being right as it is about discovering the unknown. In science being wrong is not a sin or failure but is part of the process, it's why there is peer-review.
Chastening for being wrong would discourage scientists to try, in order to avoid the risk of being chastened, and thus would hinder progression of science.

TooMany
2012-May-22, 05:06 PM
It also implies a poor understanding of how science works.
Science is not so much about being right as it is about discovering the unknown. In science being wrong is not a sin or failure but is part of the process, it's why there is peer-review.
Chastening for being wrong would discourage scientists to try, in order to avoid the risk of being chastened, and thus would hinder progression of science.

Well, we all agree about the way science should work. I cannot say with any certainty that there is prejudice against new or different ideas, but I have seen that claimed by a number of astronomers who's ideas are not strictly mainstream. I certainly agree that every new paper that comes out is not necessarily correct. Deductions that lead to conclusions are so complicated that the conclusion are somewhat fragile (on any side of the issue). Only time and more research will resolve the issues. In the meantime I'll remain open minded about the possibilities. In my mind (being blissfully ignorant) everything is on the table and nothing is truly written in stone.

noncryptic
2012-May-23, 11:14 AM
Apparently any prejudice against new (initially non-mainstream) ideas is not so strong that science can not progress, as it has done for centuries.

TooMany
2012-May-23, 11:38 PM
Apparently any prejudice against new (initially non-mainstream) ideas is not so strong that science can not progress, as it has done for centuries.

No, it just takes a few decades after the idea is introduced. Ultimately it could only be stopped by absolute authorities and history shows that those fade within ~ 1,000 years.

Cougar
2012-May-24, 01:05 AM
No, it just takes a few decades after the idea is introduced.

This is ridiculous. You imply that scientists are brainless automatons. I beg to differ.

pzkpfw
2012-May-24, 02:15 AM
TooMany has been infracted (in a different thread) for extending this view of science into a general slur against BAUT members. Let's all drop that side topic from this thread.

TooMany
2012-May-24, 11:59 PM
OK, let's get back on subject. In recent years some corrections have been made in that galaxies have more baryonic matter than previously thought due to 1) underestimated dust (which hides stars), 2) larger contribution in the low mass IMF, 3) miscount of small stars because they are hidden in bright clusters with large stars, 4) the existence of a hot corona of plasma surrounding galaxies and perhaps others. I don't know what all of this actually adds up to now. There are various estimates of how much missing mass there is in galaxies. I'm not sure how sensitive they are to assumptions about the distribution of that mass. Let's forget about the CMB conclusions for a second and just think about the distribution of matter and DM in a typical spiral. How much ordinary matter is actually required to account for rotation curves if that extra ordinary matter is optimally distributed? I ask this because the usual assumption is that the DM is non-baryonic and more or less spherically distributed over a much larger volume than the ordinary matter. I suppose the amount of DM required to explain the rotation curves is based on this type of distribution. Certainly one baryonic possibility is that it is in fact distributed like the proposed non-baronic matter, but that doesn't seem likely because the properties are so different.

Would anyone care to offer some information? In this case you have to imagine that there is no non-baryonic matter, but instead there is some "hidden" baryonic matter. What is the minimum amount needed? Do you have a reference?

StupendousMan
2012-May-25, 11:56 AM
I'm giving an exam soon. One of the problems is related to this question, so why don't I throw it out for BAUTers to do?

Below is the rotation curve of a relatively nearby galaxy. It shows radial velocity (km/s) on the vertical axis, and angular distance (arcsec) from the center of the galaxy on the horizontal axis. The distance modulus to this galaxy is about (m-M) = 27.9 mag, so the distance is about 4 Mpc.

(If you can't see the picture, look at http://stupendous.rit.edu/richmond/temp/ugc7321_rot.gif)

16941

Please estimate the amount of mass the galaxy must have (out to some radius) in order to explain the observed rotation curve. Feel free to distribute the mass in any way you wish.

The apparent V-band magnitude of this galaxy is around m(V) = 11.4. What is the absolute magnitude? Express the galaxy's luminosity in solar units.

What is the mass-to-light ratio of the galaxy you derived? Could that ratio be explained by any reasonable stellar mass function? If so, what are the parameters of that mass function?

Have fun!

Cougar
2012-May-25, 01:11 PM
It shows radial velocity (km/s) on the vertical axis, and angular distance (arcsec) from the center of the galaxy on the horizontal axis.

What's with the negative angular distance from the center?

StupendousMan
2012-May-25, 01:31 PM
In essence, positive = East of center, negative = West of center.

Cougar
2012-May-25, 02:13 PM
In essence, positive = East of center, negative = West of center.

Thank you. :o

antoniseb
2012-May-25, 02:33 PM
I'm giving an exam soon. One of the problems is related to this question, so why don't I throw it out for BAUTers to do?

Below is the rotation curve of a relatively nearby galaxy. It shows radial velocity (km/s) on the vertical axis, and angular distance (arcsec) from the center of the galaxy on the horizontal axis. The distance modulus to this galaxy is about (m-M) = 27.9 mag, so the distance is about 4 Mpc.

(If you can't see the picture, look at http://stupendous.rit.edu/richmond/temp/ugc7321_rot.gif)

16941
...

Most of us get this, but just to make it clear, this graph is NOT the milky way, it is a galaxy we are seeing close enough to edge-on that the velocities we see are the close to the average velocity of stars coming straight at us in a circular orbit. There are stars at that same radius that are moving in a different part of a wider orbit, and would seem slower by a cosine, but this chart isn't showing them.