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Russ
2001-Nov-05, 08:32 PM
I would like to open this up for general discussion. Feel free to join in.

For years I've been reading articles about "Dark Matter" which is binding together galaxies that would fly apart from angular momentum if there was only the gravity of the visible matter to work with. There has been much argument over whether it is WIMPs, MACHOs, neutrinos, some fantastic yet unknown particles, etc. ad infinitum.

I have been reading just such an article in the September 2001 issue of Sky & Telescope (yes I'm that far behind). It got my feeble brain working and...I had an idea.

Stellar mass black holes (BH) are quite small in general. The event horizon would be only a few tens to hundreds of miles in diameter. Practically speaking no bigger than a good sized astroid. What if these BH are common rather than rare? What if there are tens or hundres of billions of four to ten solar mass BH with EH's of 100 miles diameter or less, in solitary orbit of the Milkyway? How would they manifest themselves?

I know gravitational lensing and stellar purturbations. But would these events be common enough to draw our attention? I would think that picking a 100 mile BH out of the background at 5,000 ly would be pretty tough, even if there were millions. Especially in the halo, I'd think they'd be so seperate and solitary that they'd disapear except in the rare event they passed infront of something.

Any of you Professional Astronomers/Scientists know anything about this? I'd love to hear your dissertations on the topic. Anybody?

ToSeek
2001-Nov-05, 08:37 PM
Wasn't there an investigation some time ago looking at a nearby globular cluster to check for occultations? The goal was to find planets, but I think it would also have found small black holes, brown dwarfs, or any other sort of dark object were they numerous enough to be floating between here and there.

Russ
2001-Nov-05, 09:24 PM
On 2001-11-05 15:37, ToSeek wrote:
Wasn't there an investigation some time ago looking at a nearby globular cluster to check for occultations? The goal was to find planets, but I think it would also have found small black holes, brown dwarfs, or any other sort of dark object were they numerous enough to be floating between here and there.


To the best of my understanding they have seen some occultations/microlensing but not as much as they'd hoped. They don't know if this is because there are fewer objects or smaller objects. The S&T article I've been reading is actually on gravitational lensing not dark matter but their discussions on lensing prompted my idea.

I'm hoping for enlightenment from the established intelegensia here at da BABB. /phpBB/images/smiles/icon_wink.gif

Mr. Wree
2001-Nov-05, 11:01 PM
Well, not yet in answer to your question, it seems to me that the fact that data from COBE (http://space.gsfc.nasa.gov/astro/cobe/cobe_home.html), BOOMERANG (http://www.physics.ucsb.edu/~boomerang/), and MAXIMA (http://cfpa.berkeley.edu/group/cmb/) together confirm that the universe is flat (will expand forever), coupled with data from www.slac.stanford.edu/econf/C990809/docs/perlmutter.pdf+%2Bsuper+%2Bnova+%2Bexpansion+%2Bac celerating&hl=en]recent (http://www.google.com/search?q=cache:7O_RubVW180:[url) studies[/url] of supernovae indicating that the rate of expansion of the universe is increasing, says to me that really it doesn't matter a whole bunch what the actual proportional distribution of matter types is as, together, they are not enough to halt the expansion of the Universe.

Certainly, some of the 'missing mass' may be in the form of halo, small mass BHs, and such BHs indeed may help to control the shape of galaxies with too much angular momentum to otherwise persist on their own.

But, are they so significant a part of the 'missing mass' that they also exist in intergalactic space in sufficient numbers to produce the galaxy clumping of the galactic clusters and super clusters?

If so, from what in the intergalactic medium did they form? If not, how universally contributive can they be beyond the shaping of mere galaxies?

I realize your question was more limited in scope, and I thought defining such limits might help.

/phpBB/images/smiles/icon_wink.gif

<font size=-1>[ This Message was edited by: Mr. Wree on 2001-11-05 18:06 ]</font>

Russ
2001-Nov-06, 02:55 PM
You are correct. My question did not extend to cosmic expansion rates or the Open/Closed universe issue. But you bring up interesting extrapolations.



Certainly, some of the 'missing mass' may be in the form of halo, small mass BHs, and such BHs indeed may help to control the shape of galaxies with too much angular momentum to otherwise persist on their own.


True, but it would seem that they would be readilly detectable on some level. By the physical size standard they'd be too small to "see", I would think, but it seems to me there would be some manifestation of huge numbers of BH's in the halo. Or, would there?


But, are they so significant a part of the 'missing mass' that they also exist in intergalactic space in sufficient numbers to produce the galaxy clumping of the galactic clusters and super clusters?

Again you bring up a good extrapolation of my original question. But if they do exist in sufficient quantities to caust galactic clumps & strings, why can't we "see" them one way or another? Does their small size and huge mass consipre to make them invisible from a practical standpoint?



If so, from what in the intergalactic medium did they form? If not, how universally contributive can they be beyond the shaping of mere galaxies?


As far as thier formation, I'd think there'd be two possibilities. (1) They are primordial. Formed by the BB itself. (2) They formed from the first generation of supermassive stars that went super nova within the first few million years of the universe. In either case, I'm sure there'd have to be thousands of trillions of them. Given the calculated mass of the dark matter they'd have to be hugely massive and hugely populace.



I realize your question was more limited in scope, and I thought defining such limits might help.

/phpBB/images/smiles/icon_wink.gif

<font size=-1>[ This Message was edited by: Mr. Wree on 2001-11-05 18:06 ]</font>


Thanks for your contribution to my education. /phpBB/images/smiles/icon_smile.gif I am still anxious to hear what others think.

Mr. Wree
2001-Nov-07, 01:18 AM
<<...(1) They are primordial. Formed by the BB itself...>>

Consider that true, then their spacetime distribution would be uniform (as is the cosmic microwave background), and essentially identical to their distribution within galaxies, less a certain number attributable to a localized 'clumping factor'.

<<...(2) They formed from the first generation of supermassive stars that went super nova within the first few million years of the universe...>>

Presumably, they then would share the same lumpy distribution as the galaxies since galaxies seem to have begun to form fairly early in time.

Would there be a significant mass difference between halo and intergalactic BHs? Would intergalactic BHs be more like halo BHs, of steller mass, or mega-steller mass like the BHs that formed at the the cores of galaxies?

Another mechanism from which halo and extra-galactic BHs could form: compressed, wake-trailing gases from colliding galaxies. There has to have been a very great many such collisions in the early to mid-history universe.



<font size=-1>[ This Message was edited by: Mr. Wree on 2001-11-07 04:14 ]</font>

Russ
2001-Nov-08, 02:24 AM
On 2001-11-06 20:18, Mr. Wree wrote:
<<...(1) They are primordial. Formed by the BB itself...>>

Consider that true, then their spacetime distribution would be uniform (as is the cosmic microwave background), and essentially identical to their distribution within galaxies, less a certain number attributable to a localized 'clumping factor'.


Well, yes. That would be consistant with my hypothesis about them being an integral part of a typical galaxy. A reasonably uniform distribution would mean that they are part of galaxies and inter-galactic space causing the galaxy dynamics we see.


<<...(2) They formed from the first generation of supermassive stars that went super nova within the first few million years of the universe...>>

Presumably, they then would share the same lumpy distribution as the galaxies since galaxies seem to have begun to form fairly early in time.


Again, correct. Basically for the reasons I offered in my first response above.



Would there be a significant mass difference between halo and intergalactic BHs? Would intergalactic BHs be more like halo BHs, of steller mass, or mega-steller mass like the BHs that formed at the the cores of galaxies?

I would think that they'd be pretty much evenly divided among Stellar mass, Kstellar (1000's)mass, with a few meggas thrown in just because we know they exist and should be there in some number.


Another mechanism from which halo and extra-galactic BHs could form: compressed, wake-trailing gases from colliding galaxies. There has to have been a very great many such collisions in the early to mid-history universe.


????I've not heard of this as a source of BH's. I'm not saying that it couldn't happen just that I'm not familiar with such a BH creating mechanism.

We've kinda drifted afield here. I'm still interested to find out if BH's could account for the missing mass in galaxies that keeps them from flying apart due to angular momentum. All while not making themselves obvious enough for us to not have found them by now. Same for galaxy clusters too.

How about it BABBsters? Anybody know?

Azpod
2001-Nov-09, 05:50 PM
Primordial (sub-stellar mass) BHs would evaporate quickly. While there could be a good number of them near stellar mass, there would be very few with the mass of a planet left after the BB. While these BHs could explain some of the missing mass, we're talking about upwards of 90% of the mass of the universe! If even a sizeable chunk of the missing mass is sub-stellar mass BHs, they would be as common, if not more so, than stars themselves.

Actually, based on observations to date, the number of a type of object is related to the mass of the object. Large mass objects such as huge stars, black holes and neutron stars are vanishingly rare. Even stars as large as the Sun are extremely rare. Even though the Sun may not be a terribly HUGE compared to some of the giants out there, it is still more massive than 90% of the stars that are in our galaxy. Likewise, the most common star (by a LONG shot) is a red dwarf. Just taking a survey of the stars within 100 light years, almost all of them are red dwarfs.

It is difficult to observe anything smaller than a red dwarf star, because brown dwarfs emit very little light and/or radiation, and planets emit none at all. However, if the trend we see with stars continues to lower mass objects, we would expect to see even more brown dwarfs than red dwarfs, and planet-sized objects or smaller may be the most plentiful of them all.

In fact, when we refine our equipment to detect these objects, we may find that most of the otherwise empty space between the stars is littered with these cosmic burn-outs. We could have a brown dwarf floating within a light year of us, and we wouldn't know it! I don't know if there could be enough of these objects to make up the missing mass, but it could make up a sizeable chunk of it.

I'm not saying that primordial BHs couldn't make up a good portion of the missing mass. The mass of the photons, neutrinos and other particles, brown dwarfs and smaller objects and possibly yet to be discovered objects are the likely candidates for this missing matter. The main debate isn't on what it could be, but is on what proportions of each are responsible for the matter that we cannot currently detect.

When we get the ability to detect more of this matter, we will have a better idea on what makes it all up.

Russ
2001-Nov-11, 12:33 AM
On 2001-11-09 12:50, Azpod wrote:
Primordial (sub-stellar mass) BHs would evaporate quickly. While there could be a good number of them near stellar mass, there would be very few with the mass of a planet left after the BB. While these BHs could explain some of the missing mass, we're talking about upwards of 90% of the mass of the universe! If even a sizeable chunk of the missing mass is sub-stellar mass BHs, they would be as common, if not more so, than stars themselves.


This is good stuff. /phpBB/images/smiles/icon_smile.gif I don't recall mentioning that I thought the primordial BH's would be Sub Stellar Mass (SSM). In fact I don't think it occured to me that they might be SSM. An intersting thought none the less.
My line of thought about the BH's is that, even superstellar mass BH's would still be microscopic on a galactic scale. Even a BH of 10 stellar masses would have an event horizon diameter of 1000 to 2000 miles or so. One of my questions is, With this in mind, would they be detectable if they constituted the "missing mass"?



Actually, based on observations to date, the number of a type of object is related to the mass of the object. Large mass objects such as huge stars, black holes and neutron stars are vanishingly rare. Even stars as large as the Sun are extremely rare. Even though the Sun may not be a terribly HUGE compared to some of the giants out there, it is still more massive than 90% of the stars that are in our galaxy. Likewise, the most common star (by a LONG shot) is a red dwarf. Just taking a survey of the stars within 100 light years, almost all of them are red dwarfs.


Another good point that extrapolates on my original postulate. OK, maybe the "missing mass" is sub stellar objects such as brown dwarfs and rogue planets. How detectable would these be? Is it even possible that there could be that much space junque "out there" to account for the missing mass? If there is, could we have missed it for this long?



It is difficult to observe anything smaller than a red dwarf star, because brown dwarfs emit very little light and/or radiation, and planets emit none at all. However, if the trend we see with stars continues to lower mass objects, we would expect to see even more brown dwarfs than red dwarfs, and planet-sized objects or smaller may be the most plentiful of them all.


I'll agree to that. What does this imply about the missing mass situation? I know there is a study going on right now to catch MACHO's occulting and lensing background stars and galaxies. They have had some success but not as much as expected if normal barrionic matter is the missing mass. This tells me that the number of objects constituting this mass is lower than expected. So how do you get enough mass with fewer objects? How 'bout BH's?



In fact, when we refine our equipment to detect these objects, we may find that most of the otherwise empty space between the stars is littered with these cosmic burn-outs.

snip

For what it's worth, this is my gut feel for the situation as well.



We could have a brown dwarf floating within a light year of us, and we wouldn't know it! I don't know if there could be enough of these objects to make up the missing mass, but it could make up a sizeable chunk of it.


Again, this is my gut feel for the situation. So that still leaves us with the question, how detectable would this stuff be if it's really there?



I'm not saying that primordial BHs couldn't make up a good portion of the missing mass. The mass of the photons, neutrinos and other particles, brown dwarfs and smaller objects and possibly yet to be discovered objects are the likely candidates for this missing matter. The main debate isn't on what it could be, but is on what proportions of each are responsible for the matter that we cannot currently detect.


Here is where I'll start to differ with you a little. I'm sure that sub-atomic particles and photons account for a fraction of the mass. It offends my "sense of the Force", however, to think that they would be a significant fraction of the missing mass. I have no scientific proof of that, just a gut feel.



When we get the ability to detect more of this matter, we will have a better idea on what makes it all up.


No question of this being true. The better we can see, the more we will know.

Thank you for participating in my little forum. I look forward to your comments on my comment. Keep up the good work

How about you TBA? Do you have anything to toss on the fire? (so to speak)

Kaptain K
2001-Nov-11, 02:20 AM
Even a BH of 10 stellar masses would have an event horizon diameter of 1000 to 2000 miles or so.
Off by a factor of three (approx.)
A 10 solar mass BH would have a Schwartschild radius in the single digits (miles).
Hopefully, helpfully, nit-pickingly yours.

Azpod
2001-Nov-12, 08:21 PM
I'll forego the multiple nested quotes to keep this readable! /phpBB/images/smiles/icon_smile.gif I think you and I agree a great deal on the general idea of the missing mass of the universe. The particulars of the debate, of course, will be a subject of disagreement for years to come among astronomers, professional and amateur alike.

That said, in response to some of your comments, stellar mass (meaning ~1-10 solar masses) BHs are very hard to detect if they aren't actively sucking in matter. However, gravitational lensing would occur if there were a lot of BHs, of any mass. Even though the event horizon is very small on a galactic scale, the gravitational effects aren't small at all. A 10 solar mass BH would affect the movement of the nearby stars in a way that could be detected. A lot of them (and there would be a LOT of them if they make up a sizeable chunk of the missing mass of the universe) would make them easier to detect, because there would more more of them to detect, and because they would be closer to us.

Sub-stellar objects would likewise have to be very common to make up a sizeable chunk of the missing mass, but they would be much harder to detect. Individually, they would have a very small gravitational lensing effect, and would be nearly impossible to effect using that techique. The best way to detect them would be to try to find the blackbody radition that larger such objects would emit. Hi-res infrared imaging could help find some of the closer and more massive objects, and we could extrapolate from that the likely distribution of sub-stellar objects throughout the galaxy.

Personally, I hope that happens. It would be exciting to find a brown dwarf or an ejected gas giant just outside our solar system, and be able to send a probe to it.

As for particles such as neutrinos and such being a sizeable portion of the missing mass, it is quite possible. While they would have only a tiny amount of mass each, if they did have mass, it would add up to a sizeable portion of the mass of the universe simply because there are a lot of them! Neutrinos, for instance, pass through every gram of matter on Earth, and there are a lot of them that pass through us every second. There is already indications that they do have mass, and if we will likely find out that the mass that they do have could add up to a significant fraction of the missing mass of the universe. What will that fraction be? I don't know; like I said, that subject will likely be a matter of serious debate for many years to come.

_________________
Just my two neurons worth,
Azpod... Formerly known as James Justin

<font size=-1>[ This Message was edited by: Azpod on 2001-11-12 15:22 ]</font>

Espritch
2001-Nov-13, 03:38 AM
Just a random thought. What if gravity is not linearly proportional to the amount of matter but is related on a curve. On the local level (i.e. the solar system) this effect would not be significant because the amount of matter is small. But at the scale of the Galaxy, the amount of matter is much greater and would be much further along the curve so the cumulative gravitational effect would be much greater. If this were so, large amounts of dark matter might not be needed to hold the Galaxy together.

Russ
2001-Nov-13, 12:34 PM
On 2001-11-10 21:20, Kaptain K wrote:
Off by a factor of three (approx.)
A 10 solar mass BH would have a Schwartschild radius in the single digits (miles).
Hopefully, helpfully, nit-pickingly yours.



Thanks for the correction. I was working from a memory of a memory of a thought of an article I read many moons ago. /phpBB/images/smiles/icon_smile.gif

Russ
2001-Nov-13, 01:18 PM
On 2001-11-12 15:21, Azpod wrote:
I'll forego the multiple nested quotes to keep this readable! /phpBB/images/smiles/icon_smile.gif

Me too.

I think you and I agree on most of this stuff too. The thing I can't seem to get anybody to say is, whether or not they agree with all of the speculation about exotic matter making up the missing mass. I am very reluctant to agree with something exotic but do not have the astronomical background education to refute the pro's.

What got me going on this is a short article I read, by Jeff Marcy talking about extra-Solar planets. He mentioned that most of what has been found so far is in unstable orbit around the host star. This will cause the planet to be either ejected from or swallowed by the star. OK, I can follow that easily.

Let's extrapolate a little. It seems most stellar systems develope planets. I've read that it's possible that our system had more but they were gravitationaly ejected sometime back. If 70% (a SWAG number) of stars created have planets and 70% of those eject one or more of the planets then there would have to be Trillions of ejecta-planets floating around the galaxy.

They'd be too small & dim to see in the traditional sense. They'd be too low mass to cause stellar purtubations, gravitational lensing or occultations. They'd probably cool to just above 3 degrees K. Fundamentally, they'd be invisable to anything but the coldest IR telescopes. Of which we've made none.

I fell into the BH thought line as they would be extreemly massive for their volume and would also tend to eject or be ejected and, if alone, would be VERY HARD to detect. I think ejecta-planets are a possibility but think they'd show up as "dust" or other light blocking matter if they were in sufficient quantities to account for the missing mass.

As far as photons, neutrinos, etc. go, I know they would contribute a fraction of the total universal mass, but doubt they'd contribute to the "galactic missing mass" (GMM). I think this because they are so unpreturbed by the rest of the universe they would not be associated with any individual galaxy.

I think I've confused myself here. I'll stand down and listen to yall for a while. Any one out there have an apposing point of view?

Russ
2001-Nov-13, 01:32 PM
On 2001-11-12 22:38, Espritch wrote:
Just a random thought. What if gravity is not linearly proportional to the amount of matter but is related on a curve. On the local level (i.e. the solar system) this effect would not be significant because the amount of matter is small. But at the scale of the Galaxy, the amount of matter is much greater and would be much further along the curve so the cumulative gravitational effect would be much greater. If this were so, large amounts of dark matter might not be needed to hold the Galaxy together.


I'm no expert but as I understand it, the non-linear effects in grav. law are in the distance partial of the equation. In short the gravitational effect is inversly proportional to the square of the distance between the centers of mass.

What that means is, the gravitational attraction will vary in a linear relationship based on mass but will vary in a non-linear relationship (square root) with distance. As these laws have been studied over 400 years, proven and re-proven many times, I really doubt that your scenario would be the case.

Have you read/seen something reciently that spoke of what you describe? I've not heard of it so far.

Espritch
2001-Nov-14, 02:01 AM
I really doubt that your scenario would be the case.

Have you read/seen something reciently that spoke of what you describe? I've not heard of it so far.

I'm no expert on this subject either. As I noted, this is purely speculation on my part. I was just wondering if physicists know for certain if the effect of gravity really is linearly proportional to the amount of matter? A very gradual curve would look linear over a relatively short sample range unless you have very sensitive measuring capabilities. I assume that most of our observations of gravity involve matter on Earth or the orbital behavior of the planets in our own solar system and this is a rather small sample compared with an entire galaxy.

The basic reason for positing the the existence of dark matter (well one of them anyway) is that the angular momentum of the galaxy should tear it apart based on the amount of light matter observed. So they assume there must be a lot of matter that we don't see. But so far they haven't really had much success in finding this dark matter. I was just wondering if there might be another explanation.

Russ
2001-Nov-14, 08:11 PM
I'm no expert on this subject either. As I noted, this is purely speculation on my part. I was just wondering if physicists know for certain if the effect of gravity really is linearly proportional to the amount of matter? A very gradual curve would look linear over a relatively short sample range unless you have very sensitive measuring capabilities. I assume that most of our observations of gravity involve matter on Earth or the orbital behavior of the planets in our own solar system and this is a rather small sample compared with an entire galaxy.

The basic reason for positing the the existence of dark matter (well one of them anyway) is that the angular momentum of the galaxy should tear it apart based on the amount of light matter observed. So they assume there must be a lot of matter that we don't see. But so far they haven't really had much success in finding this dark matter. I was just wondering if there might be another explanation.


To the best of my knowledge, the the gravitation experts pretty much agree that the linear relationship of mass to gravity is settled. If it were non-linear on a galactic, group or cluster scale then it would show up in the way these large scale structures orbit each other.

As far as the orbital dynamics of galaxies is concerned, you are correct. To the best of anybodies understanding right now, most galaxies would fly appart if you only have "visible" matter to work with. The fact that they don't fly apart is what got the whole discussion on dark/exotic matter going.

What motivated me to start this thread is my reluctance to believe in some type of exotic matter that does not obey the "known" laws of physics. My "Sense Of The Force" is that it must be some blend of solo BH's, and rogue planets rather than what I call "magical matter". I was hoping this thread would attract some informed dissertation from the pro's and exceptionally well informed who haunt the BABB.

How about it folks?

ToSeek
2001-Nov-14, 09:16 PM
On 2001-11-13 21:01, Espritch wrote:

The basic reason for positing the the existence of dark matter (well one of them anyway) is that the angular momentum of the galaxy should tear it apart based on the amount of light matter observed. So they assume there must be a lot of matter that we don't see. But so far they haven't really had much success in finding this dark matter. I was just wondering if there might be another explanation.



The primary alternative to dark matter is a hypothesis called "Modified Newtonian Dynamics" (MOND for short), which conjectures that the inverse square law no longer applies to gravity (or inertia) at extremely low accelerations. (And by extremely low accelerations we're talking angstroms per second per second.) If gravity is just a tiny bit stronger under these conditions, then no dark matter is required.

Proponents claim that the latest observations of the cosmic microwave background radiation support MOND.

The MOND Pages (http://www.astro.umd.edu/~ssm/mond/index.html)

Russ
2001-Nov-14, 09:55 PM
On 2001-11-14 16:16, ToSeek wrote:

The primary alternative to dark matter is a hypothesis called "Modified Newtonian Dynamics" (MOND for short), which conjectures that the inverse square law no longer applies to gravity (or inertia) at extremely low accelerations. (And by extremely low accelerations we're talking angstroms per second per second.) If gravity is just a tiny bit stronger under these conditions, then no dark matter is required.

Proponents claim that the latest observations of the cosmic microwave background radiation support MOND.

The MOND Pages (http://www.astro.umd.edu/~ssm/mond/index.html)


Yeaaaaahhhhh, I've read about MOND (in SciAm) but it sounds more like an excuse than an explanation to me. I envision:.....blurry, undulating fade to college lab:

Grad Student: (shakes head and tosses papers on desk) "People are gonna wanta know why galaxies hold together even though there's not enough visible mass to account for the fact that they do."

Desperate Astronomer: (waves pipe at GS & points at papers with it) "Well they aren't swallowing the WIMP's or other wierd particle junk we've thrown at 'em. Let's think up another ** principal with a catchy acronym and see if they buy off on that."

Blurry, undulating fade back to reality.

I admit that my little passion play there is a characature of a cartoon of my sarcastic outlook, but.... well you get the idea.

The Curtmudgeon
2001-Nov-14, 10:21 PM
Thanx for that link, ToS! I can't begin to claim that I followed all the details, but it certainly gives one furiously to think.

The (but now my brain hurts again) Curtmudgeon

ToSeek
2001-Nov-15, 01:32 PM
On 2001-11-14 16:55, Russ wrote:

Yeaaaaahhhhh, I've read about MOND (in SciAm) but it sounds more like an excuse than an explanation to me. I envision:.....blurry, undulating fade to college lab:

Grad Student: (shakes head and tosses papers on desk) "People are gonna wanta know why galaxies hold together even though there's not enough visible mass to account for the fact that they do."

Desperate Astronomer: (waves pipe at GS & points at papers with it) "Well they aren't swallowing the WIMP's or other wierd particle junk we've thrown at 'em. Let's think up another ** principal with a catchy acronym and see if they buy off on that."



Well, both explanations right now are pretty much ad hoc. It remains to be seen which one becomes more reasonable - the MAP results should help with this.

Russ
2001-Nov-15, 09:27 PM
Well, both explanations right now are pretty much ad hoc. It remains to be seen which one becomes more reasonable - the MAP results should help with this.


Yeah, but I want to know NOW! NOW! NOW! NOW! (stamps foot & holds breath)

ToSeek
2001-Nov-16, 02:44 PM
On 2001-11-15 16:27, Russ wrote:


Well, both explanations right now are pretty much ad hoc. It remains to be seen which one becomes more reasonable - the MAP results should help with this.


Yeah, but I want to know NOW! NOW! NOW! NOW! (stamps foot & holds breath)



I know the feeling - I feel the same way about SETI. /phpBB/images/smiles/icon_wink.gif

The Bad Astronomer
2001-Nov-16, 03:56 PM
On 2001-11-09 12:50, Azpod wrote:
Primordial (sub-stellar mass) BHs would evaporate quickly. While there could be a good number of them near stellar mass, there would be very few with the mass of a planet left after the BB.


Hmmm... you have sparked a thought. When we look at very distant clusters of galaxies, we still see that they are "missing" roughly the same mass that nearby clusters are. That may imply that the missing mass is constant in time, in other words, it was the same a long time ago as it is now. That would eliminate small BHs as the cause; there are fewer now.

This is a very shaky argument, I'll admit. I am not sure how far back we have looked for missing mass; it may only be a small fraction of the age of the Universe (maybe half?). This is not really my field, so I won't try to quantify it. Just a thought.

Russ
2001-Nov-16, 04:31 PM
Hmmm... you have sparked a thought. When we look at very distant clusters of galaxies, we still see that they are "missing" roughly the same mass that nearby clusters are. That may imply that the missing mass is constant in time, in other words, it was the same a long time ago as it is now. That would eliminate small BHs as the cause; there are fewer now.

This is a very shaky argument, I'll admit. I am not sure how far back we have looked for missing mass; it may only be a small fraction of the age of the Universe (maybe half?). This is not really my field, so I won't try to quantify it. Just a thought.


Hey BA: Now that We seem to have your attention... Maybe you could answer some of the quesions from above?

How would huge numbers of small (3-10 SM) BH's manifest themselves in the halo? Is it even possible that small BH's could be the missing mass? Could Jillions of Earth mass rogue planets constitute the missing mass? Would they have a side effect that we should/would have noticed by now?

If you don't know the answer to some of these questions, could you point us at someone who does?

roidspop
2002-Apr-05, 03:51 AM
MOND? This BB is so great! I must have flipped past that article in SciAm going for the centerfold.

Any ideas about an experiment that could detect this effect? Maybe the gravity wave telescopes are sensitive enough to be used as detectors foooorrrr....(help me out here...) accelerating a dump truck with a pocket laser pointer? What would Cavendish do?


<font size=-1>[ This Message was edited by: roidspop on 2002-04-04 22:52 ]</font>