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View Full Version : progenitors of type 1a supernova....identification of single or double degenerates



trinitree88
2011-Jul-30, 02:59 PM
Mario Livio and company have proposed a new test for identifying whether or not type 1a's are formed from single or double bodies. The conventional wisdom, which as yet is unable to choose between the two, favors either a single mass accreting carbon/oxygen white dwarf (CO WD).that draws off hydrogen/helium gas from a main sequence or subgiant or bloated red giant companion, which goes off when it reaches the theoretical Chandra limit..or..a pair of CO WD in a binary gradually succumb to the inspiraling due to general relativistic effects of emitting gravitational radiation, and combine their kinetic energy and momenta.
They consider the inherent asymmetry in the explosions,( first proposed as the source of pulsar kicks in the mid 70's by I.I.Schlovskii...)and the use of polarization studies coupled with velocity gradients and carbon signatures in the ejecta to determine whether the single denerate (SD) or double degenerate (DD) scenario is exclusive. Larger carbon signatures should favor the latter from their models.




SEE:http://arxiv.org/PS_cache/arxiv/pdf/1107/1107.5729v1.pdf

SEE animation of white dwarf merger:http://www.youtube.com/watch?v=yMnnq0jnfQE

SEE: Tycho's animation of 1572:http://www.videosurf.com/video/tycho%27s-supernova-explosion-in-1572-animation-79776810

Jerry
2011-Aug-09, 05:11 AM
I'm always leery of false dichotomies. Both lineages could be either correct or incorrect. Still, it is nice to see research focused at eliminating an option.

Messier Tidy Upper
2011-Aug-09, 04:38 PM
My guess would be that both mechanisms - nicely illustrated in this :

http://blogs.discovermagazine.com/badastronomy/2010/02/18/dwarf-merging-makes-for-an-explosive-combo/

Bad Astronomy blog comment are possible and occur. Both ideas make sense and I can't see any reason why either wouldn't occassionally happen.

This thread /news peice via 80beats :

http://blogs.discovermagazine.com/80beats/2011/04/28/tychos-supernova-went-boom-after-slurping-up-some-of-its-neighbor/

regarding Tycho's supernova could be interesting / relevant / worth reading here too.

Jerry
2011-Aug-23, 04:32 AM
It turns out that the two different scenarios leading up to the explosion have two very different effects: accretion makes a lot of X-rays, while a merger does not. So astronomers did what you’d expect: they pointed the Chandra X-Ray Observatory at a bunch of galaxies and observed supernovae. What they found was pretty surprising: the amount of X-rays from Type Ia supernovae in nearby galaxies was 30 – 50 times lower than what would be expected from accretion. In other words, their observations strongly favor the idea that it’s the merger of white dwarfs that cause Type Ia supernovae.

Well! I was pretty surprised to hear that. Like other astronomers, I figured it was accretion that was the culprit.


Later, the BA askes the obvious question:


If Type Ias are caused by a different scenario than previously thought, could it mean that our measurements of the distant Universe are wrong?

To which there is a less than obvious answer:


I asked this question specifically at the Chandra press conference, and was told that the two different scenarios produce explosions with pretty much the same energy, so this may only affect cosmological measurements a small amount.

But there is a better answer stirring in the BA's own surmise:


This has some interesting ramifications. It certainly affects a lot of fields of astronomy, like how binary stars form and change over time. But it may also affect cosmology, the study of the birth, evolution, and eventual fate of the Universe itself. If Type Ias are caused by a different scenario than previously thought, could it mean that our measurements of the distant Universe are wrong?

The better answer is "Of course it could". We get to be wrong because we are making great extrapolations to the neather end of a very large visible universe. The best answer is that such a gross extrapolation is more likely wrong, that right, but it is the best guess at this moment.

Finally:


My gut reaction is that this won’t matter a huge amount, since we have lots of independent ways of measuring dark energy, and they all appear to be in rough agreement.

'Rough agreement' can also be taken as a sign that parametric assumptions made by other research groups are biased towards the confidence staked in the original assumptions about supernova events.

This happened when the Hubble Space Telescope Key Project plucked down a standard value for Hubbles constant, and there was a dramatic shift in error bars of subsequent papers studying the distance modules from many different angles. In a perfect research world, that shouldn't happen.

See also http://arxiv.org/abs/astro-ph/0308099v1 Non-Gaussian Error Distribution of Hubble Constant Measurements

Tensor
2011-Aug-23, 04:47 AM
The better answer is "Of course it could. We get to be wrong because we are making great extrapolations to the neither end of a very very large visible universe. The best answer is that such a gross extrapolation is more likely wrong, that right, but it is the best guess at this moment.

And you don't think that this is why they keep doing research on this? To find out whether or not the extrapolations are correct? Isn't that why we do research?


'Rough agreement' can also be taken as a sign that parametric assumptions made by other research groups are biased towards the confidence staked in the original assumptions about supernova events.

Are you saying that those other research groups make up their own data to get the right answers?


This happened when the Hubble Space Telescope Key Project plucked down a standard value for Hubbles constant, and there was a dramatic shift in error bars of subsequent papers studying the distance modules from many different angles. In a perfect research world, that shouldn't happen.

Jerry, are you saying that those researchers were either changing their data or lying about it to get the new values they wanted?

Ken G
2011-Aug-23, 08:07 AM
I think an important thing about the use of Type Ia supernovae in cosmology is that it is not true that it is theory that sets what their luminosity is. It turns out there are many different kinds of type Ia supernovae, but their brightness connects in a simple empirical way with their light curve. It was a bit like the Cepheids of Hubble fame-- it was not models of a Cepheid that gave us the period-luminosity relation, it was just an empirical correlation that was calibrated using nearby Cepheids. As I understand it, the same is true of type Ia SN-- the idea that they are always a Chandra mass of C blowing up is just a back-of-the-envelope way of understanding why the empirical correlation exists in the first place, but the actual correlation is indeed purely empirical and doesn't care squat about what is the physical cause of type Ia. The key assumption is only that whatever mechanism causes them now has also been the mechanism for the last few billion years, and the evidence for that is that their variety of light curves look the same as now.

Jerry
2011-Aug-28, 06:26 AM
And you don't think that this is why they keep doing research on this? To find out whether or not the extrapolations are correct? Isn't that why we do research?
You can't make the assumption that one theory or the other is correct and then use a test that disproves one argument to prove that the other argument is true: You can't find a palm tree and conclude you are not in Alaska therefore you are in Hawaii.

The abundance of X-rays only means the old single white dwarf theory is suspect. We really need a smoking gun: Finding a WD or a pair of them in an earlier image that metamophs into a SNIa. It would take a fairly local event to do this, or have much more powerful tools than we have today. But the Precursor to a SNIa may be something other than binary WDs.


Are you saying that those other research groups make up their own data to get the right answers?
Simple application of the Jerry test: If the baryon oscillation dudes announced that the supernova Ia results were inconsistant with the acoustic squiggles in baryons, would everyone jump up and say: well of course all of their parametric assumptions are incontestable and the supernova groups must be wrong". No. That is the rub: there is no independent test that is less likely to have systematic errors than what we see in supernova science. Again, this does not make assumptions made in the determination of the absolute magnitudes of SN correct.



Jerry, are you saying that those researchers were either changing their data or lying about it to get the new values they wanted?
No. Everyone would love to come up with definitive tests that overturn existing theories. Evolve dinosaurs from birds rather than lizards; stuff like that. It is the hardest thing in science to do. It is the hardest thing, period.

Jerry
2011-Aug-28, 06:34 AM
I think an important thing about the use of Type Ia supernovae in cosmology is that it is not true that it is theory that sets what their luminosity is. It turns out there are many different kinds of type Ia supernovae, but their brightness connects in a simple empirical way with their light curve. It was a bit like the Cepheids of Hubble fame-- it was not models of a Cepheid that gave us the period-luminosity relation, it was just an empirical correlation that was calibrated using nearby Cepheids. As I understand it, the same is true of type Ia SN-- the idea that they are always a Chandra mass of C blowing up is just a back-of-the-envelope way of understanding why the empirical correlation exists in the first place, but the actual correlation is indeed purely empirical and doesn't care squat about what is the physical cause of type Ia. The key assumption is only that whatever mechanism causes them now has also been the mechanism for the last few billion years, and the evidence for that is that their variety of light curves look the same as now.

I think it is fair to argue that all airplanes have similar shapes, but vary widely in mass. Likewise, it is difficult to determine how much of explosive is detonating when you don't know the core specifications of the explosive. That is the rub: It was the underlying assumption that there is a critical mass that drove the acceptance of type Ia as a standard candle. It is a much more complicated assumption in the case of a binary event: the viewing angle is critical; too.

It is interesting that for the longest time, evidence of polarization in SN explosions was noted as a curiousity that did not dissuade theoriest from the singular, mass-critical event. We always weigh contrary evidence or supporting evidence differently, depending upon our background or experience. That is the human part of scientific investigation that is impossible to eliminate.

It is possible to argue that the balance of evidence has shifted and now favors a binary event; as the BA concedes. It is also possible to argue there has always been a thumb on the scale.

Jerry
2011-Aug-30, 06:56 AM
Jerry, are you saying that those researchers were either changing their data or lying about it to get the new values they wanted?
Successful Scientists are usually perfectionists. Perfectionist can find it difficult to admit to an error; especially when the error is in their core knowledge base. It is easy to overlook or discredit a set of data that disagrees with well established theories. It is difficult to publish when the results are more ambiguous than the researchers hoped they would be.

I have used the Gravity Probe B experiment as a textbook example of results that underwelm the scientific world but is still headlined:


http://www.nasa.gov/mission_pages/gpb/index.html

NASA's Gravity Probe B Confirms Two Einstein Space-Time Theories

Nice eyegrabbing, but as always, the devil is in the details. From the executive summary:

http://www.nasa.gov/pdf/168808main_gp-b_pfar_cvr-pref-execsum.pdf


The GP-B story is, therefore, a complex one, in fact, seven interfolded stories:
1.
About testing Einstein
2.
About the invention of many new technologies
3.
About a collaboration between university departments
4.
About highly successful student involvement in a long-running space program
5.
About a remarkable range of spin-offs, including drag-free technology, AutofarmŽ GPS-based precision tractor control, a novel quartz bonding technique, and the porous plug device for controlling superfluid helium in space which made possible the IRAS, COBE, WMAP and Spitzer missions
6.
About collaboration between NASA and academia
7.
About the challenge of managing a flight program with a very highly integrated payload and spacecraft which led the then-NASA Administrator, Mr. James Beggs, in 1984, to say that GP-B was not only a fascinating physics experiment but also a fascinating management experiment.

Notice that none of the seven stories is about 'confirming two aspects of general relativity'.

The executive summary also tells us


http://www.nasa.gov/pdf/168808main_gp-b_pfar_cvr-pref-execsum.pdf




GP-B's measurement of the geodetic effect has an expected accuracy of better than 0.01%. The frame-dragging effect has never directly been measured, but Gravity Probe-B is expected to determine its accuracy to ~1%.

http://einstein.stanford.edu/

The experimental results are in agreement with Einstein's theoretical predictions of the geodetic effect (0.28% margin of error) and the frame-dragging effect (19% margin of error).[/quote]

0.28/0.01 is a factor of 28 less accurate than expected and; likewise 19% is a lot move uncertainty than 1%.

But that is not the whole analytical story.

http://einstein.stanford.edu/content/final_report/GPB_Final_NASA_Report-020509-web.pdf


Summary and Conclusion The misalignment and resonance torques produced significant disturbances to the orientation of the gyroscope spin axes. These torques may be explained by the same physical effect – an interaction of patch effect fields on the surface of the rotor with patch effect fields on the surface of the housing. The misalignment torque is proportional to the misalignment between the gyroscope spin axis and the satellite roll axis. All four gyroscopes exhibited a drift rate due to the misalignment torque, but the magnitude of the torque varied considerably from one gyroscope to another and over the duration of the mission. The resonance torques, on the other hand, are independent of the misalignment to lowest order, but their frequency depends on the difference between a harmonic of the polhode frequency and the satellite roll frequency. When this frequency difference is small, they can produce a permanent offset of the gyroscope spin axis. Because of the significantly different polhode frequencies and rates of change of the polhode frequencies, the frequency of the offsets due to the resonance torques was very different for the different gyroscopes. As the polhode motion was damped out, the frequency of these resonance conditions decreased...

Two alternative data analysis methods can be used: one only uses the component of the drift rate in a direction parallel to the misalignment, the other uses the drift rate information in both directions but includes the misalignment torque coefficient as one of the parameters in the data analysis. The effects of the resonance torques may also be separated from the uniform drift rate either by not using the data during those times when the effects of the resonance torques are most pronounced or by explicitly included two additional parameters for each resonance in the data analysis.

Adding otherwise undefined parameters to fit a curve in order to prove a theory is like claiming victory in a battle never fought. In this case, they beat the numbers to death; but proved nothing.

Tensor
2011-Sep-01, 06:02 PM
You can't make the assumption that one theory or the other is correct and then use a test that disproves one argument to prove that the other argument is true: You can't find a palm tree and conclude you are not in Alaska therefore you are in Hawaii.

Can you point specifically to a recent paper and part of a paper that you think shows that the researchers claim that a Dual Detonation (DD) or a Single Detonation (SD) is wrong, so the other is correct? From my reading, the current thinking is that the possibilities are strong that both are possible.


The abundance of X-rays only means the old single white dwarf theory is suspect.

Why? Specifically. Give us the numbers that show this. If you can.


We really need a smoking gun: Finding a WD or a pair of them in an earlier image that metamophs into a SNIa. It would take a fairly local event to do this, or have much more powerful tools than we have today. But the Precursor to a SNIa may be something other than binary WDs.

And that would be, what? You have something that fits the bill Jerry? Or is it just that you are free to take pot shots without having to do anything yourself.

This is also a change in thinking for you. Just a couple of years ago, you were complaining about single progenitors and pushing double progenitors. You even presented a paper to support your idea, where the measured mass of nickel was nearly twice the mass of the Sun. Well over the the 1.44 mass limit.

And when that was pointed out to you, you started in how the paper was wrong and they didn't measure correctly. Forgetting that it was a paper you yourself presented to support SD events.



Simple application of the Jerry test: If the baryon oscillation dudes announced that the supernova Ia results were inconsistant with the acoustic squiggles in baryons, would everyone jump up and say: well of course all of their parametric assumptions are incontestable and the supernova groups must be wrong". No.

How do you know. What proof of this. I notice that you don't apply the Jerry test, to any of Jerry's ideas.



That is the rub: there is no independent test that is less likely to have systematic errors than what we see in supernova science.

Which test Jerry? What errors Jerry? See that's a problem with you. You throw around all these complaints and accusations, but never get into specifics. Or, if you do, you are usually rather quickly shown to be wrong. Usually in the very paper you present as evidence. I will also point out that you do a good job of complaining about it, but then give excuses as to why you can't write your own paper on the subject.


Again, this does not make assumptions made in the determination of the absolute magnitudes of SN correct.

It also doesn't make them wrong. Contrary to your general complaints, there are some very good reasons to suspect they are correct. What, paper, and what specific part of that paper do you claim is incorrect?



Jerry, are you saying that those researchers were either changing their data or lying about it to get the new values they wanted? No. Everyone would love to come up with definitive tests that overturn existing theories. Evolve dinosaurs from birds rather than lizards; stuff like that. It is the hardest thing in science to do. It is the hardest thing, period.

and yet, in the very next post, that is what you accuse the researchers of. To wit:


It is also possible to argue there has always been a thumb on the scale.

or in previous posts:


and there was a dramatic shift in error bars of subsequent papers studying the distance modules from many different angles.

or this:


'Rough agreement' can also be taken as a sign that parametric assumptions made by other research groups are biased towards the confidence staked in the original assumptions about supernova events.

How are these statements not a claim the researchers are cheating, lying or illegally manipulating the numbers?

Ken G
2011-Sep-02, 11:16 PM
It is possible to argue that the balance of evidence has shifted and now favors a binary event; as the BA concedes.But the binary event does not preclude the critical-mass assumption, it merely alters the accretion mechanism. It's not like a binary merger gives you a white dwarf with twice the Chandra mass, which then goes supernova! Instead, the merger creates a complicated mass distribution, which should still detonate when there is something corelike with a Chandra mass. It might yield some differences in the explosion, and probably a big difference in the detritus that comes blasting out, but even the simple Chandra implosion does not have just one model for how it would play out. This is why it is so important to recognize that the Ia SN distance scale relies on empirical observations of Ia SN, not on the models of how the explosions occur. The empirical evidence is that the total energy release is similar to the collapse of a Chandra mass, which makes the empirical fitting procedure more robust, and the theory justifies that, but it is not essential to the empirical fitting procedure. The bottom line is, it really doesn't seem to matter much which explosion mechanism is invoked, the distance scale is not going to be altered much. At least this is my impression of the situation.

Nereid
2011-Sep-03, 09:51 AM
The bottom line is, it really doesn't seem to matter much which explosion mechanism is invoked, the distance scale is not going to be altered much.
Yep.

For some reason Jerry cannot accept this, it seems. And it's not a matter of there being a lack of papers on the subject - which make this point very robustly - but some incoherent (I don't think that's too strong a word) intuition, which has never been translated into a consistent, well-supported statement or draft paper (at least not one that's publicly available).

There are, after all, multiple other methods of estimating Mpc+ distances, methods that are quite independent of SNe Ias. While they may not be good to a few tens of percent (!), they are nonetheless consistent.

But what I find really odd is that astronomers, generally, are all over SNe that look like they might be Ia outliers, or something which otherwise mimics a Ia. After all, which astronomer actively working in this field wouldn't want to be one to publish a paradigm-shifting discovery? :razz: :cool: Isn't this one of the motivations behind efforts like the Palomar Transient Factory (http://www.astro.caltech.edu/ptf/)?

For example, look at the buzz around the "Oops" supernova (http://www.galaxyzooforum.org/index.php?topic=279410.0).

Jerry
2011-Sep-04, 05:03 AM
Yep.

For some reason Jerry cannot accept this, it seems. And it's not a matter of there being a lack of papers on the subject - which make this point very robustly - but some incoherent (I don't think that's too strong a word) intuition, which has never been translated into a consistent, well-supported statement or draft paper (at least not one that's publicly available).


Why Jerry cannot accept this, is the irrationality of assuming that the most distant events we have observed-to-date are all of average, rather than exceptional magnitude. We have observed more than a handful of superluminous events now, enough at least, to suspect that the most distant events are exceptional rather than average.

When you make the assumption (like I am) that the most distant events are more reddened and brighter-than-average; then the dark energy component becomes overwhelming. One shouldn't be required to submit an alternative explanation when questioning whether or not a cosmic extrapolation is valid: One guess with a couple of unexpected variables is no better than another.

Nereid
2011-Sep-04, 10:00 AM
Yep.

For some reason Jerry cannot accept this, it seems. And it's not a matter of there being a lack of papers on the subject - which make this point very robustly - but some incoherent (I don't think that's too strong a word) intuition, which has never been translated into a consistent, well-supported statement or draft paper (at least not one that's publicly available).Why Jerry cannot accept this, is the irrationality of assuming that the most distant events we have observed-to-date are all of average, rather than exceptional magnitude.
So you have said, one way or another, for quite a while now (years?).

Yet when other BAUTians go to the trouble of demonstrating - sometimes in great detail - that your bald "assuming" is at best, well, irrational what do you do? As far as I know, of the several responses you have given, none includes "yep, I was wrong to assume that; clearly a huge amount of solid research has been done to test that", or words to that effect. In short, that assumption (if assumption it be) has been tested, many times, independently, etc, etc, etc ... but for some reason known only to you (presumably), you reject each and every bit of such research.


We have observed more than a handful of superluminous events now, enough at least, to suspect that the most distant events are exceptional rather than average.
See above.


When you make the assumption (like I am) that the most distant events are more reddened and brighter-than-average; then the dark energy component becomes overwhelming.
Quite.

Except that, as far as I know, you have yet to demonstrate - with numbers, data, and so on - the validity of this bald (bold?) claim.

Words are easy Jerry, numbers are not; unless and until you start to turn your words into numbers, no progress will ever be made, will it?


One shouldn't be required to submit an alternative explanation when questioning whether or not a cosmic extrapolation is valid: One guess with a couple of unexpected variables is no better than another.
Enough with the words already Jerry! :naughty: Data! Numerical analyses! Equations! (and so on).