Composite image of M31. Inset shows central region as seen by Chandra. Credit: NASA/CXC/MPA/ M.Gilfanov & A.Bogdan;

Chandra

Merging White Dwarfs Set Off Supernovae

17 Feb , 2010 by

New results from the Chandra X-Ray Observatory suggests that the majority of Type Ia supernovae occur due to the merger of two white dwarfs. This new finding provides a major advance in understanding the type of supernovae that astronomers use to measure the expansion of the Universe, which in turns allows astronomers to study dark energy which is believed to pervade the universe. “It was a major embarrassment that we still didn’t know the conditions and progenitor systems of some the most spectacular explosions in the universe,” said Marat Gilfanov of the Max Planck Institute for Astrophysics, at a press conference with reporters today. Gilfanov is the lead author of the study that appears in the Feb. 18 edition of the journal Nature.

Type Ia supernovae serve as cosmic mile markers to measure expansion of the universe. Because they can be seen at large distances, and they follow a reliable pattern of brightness. However, until now, scientists have been unsure what actually causes the explosions.

Most scientists agree a Type Ia supernova occurs when a white dwarf star — a collapsed remnant of an elderly star — exceeds its weight limit, becomes unstable and explodes. The two leading candidates for what pushes the white dwarf over the edge are the merging of two white dwarfs, or accretion, a process in which the white dwarf pulls material from a sun-like companion star until it exceeds its weight limit.

“Our results suggest the supernovae in the galaxies we studied almost all come from two white dwarfs merging,” said co-author Akos Bogdan, also of Max Planck. “This is probably not what many astronomers would expect.”

The difference between these two scenarios may have implications for how these supernovae can be used as “standard candles” — objects of a known brightness — to track vast cosmic distances. Because white dwarfs can come in a range of masses, the merger of two could result in explosions that vary somewhat in brightness.

Because these two scenarios would generate different amounts of X-ray emission, Gilfanov and Bogdan used Chandra to observe five nearby elliptical galaxies and the central region of the Andromeda galaxy. A Type Ia supernova caused by accreting material produces significant X-ray emission prior to the explosion. A supernova from a merger of two white dwarfs, on the other hand, would create significantly less X-ray emission than the accretion scenario.

The scientists found the observed X-ray emission was a factor of 30 to 50 times smaller than expected from the accretion scenario, effectively ruling it out.

So, for example, the Chandra image above would be about 40 times brighter than observed if Type Ia supernova in the bulge of this galaxy were triggered by material from a normal star falling onto a white dwarf star. Similar results for five elliptical galaxies were found.

This implies that white dwarf mergers dominate in these galaxies.

An open question remains whether these white dwarf mergers are the primary catalyst for Type Ia supernovae in spiral galaxies. Further studies are required to know if supernovae in spiral galaxies are caused by mergers or a mixture of the two processes. Another intriguing consequence of this result is that a pair of white dwarfs is relatively hard to spot, even with the best telescopes.

“To many astrophysicists, the merger scenario seemed to be less likely because too few double-white-dwarf systems appeared to exist,” said Gilfanov. “Now this path to supernovae will have to be investigated in more detail.”

Source: NASA

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By  -        
Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.



30 Responses

  1. Hon. Salacious B. Crumb says:

    Really the worst astrophysics article I’ve read on Universe Today.
    The information lies clearly in the detail and most if what we know about SN Ia (or SN I) here have been glossed over or just reprocessed as “new.”

    I.e. “Most scientists agree a Type Ia supernova occurs when a white dwarf star — a collapsed remnant of an elderly star — exceeds its weight limit, becomes unstable and explodes.

    OK. Who disagrees? (except perhaps those EU twits?) Really this statement was true even in the 1950s! [Zwicky, no doubt, would be turning in his grave.]

    As for; “To many astrophysicists, the merger scenario seemed to be less likely because too few double-white-dwarf systems appeared to exist,” said Gilfanov. “Now this path to supernovae will have to be investigated in more detail.

    Which astrophysicists? Whom? As far as I know the energy released in the supernova by either means in revealed in the spectra – the basis of general definition of the SNI, Ia, II, etc – and their is NO difference in the light-curves. Here the are saying, contradicting this, that the X-ray emission, ARE different. So why is the X-ray emission “40 to 50 times smaller” (A difference similar between SN I and II!

    Question: Might other explanations like the conditions in which SNIa’s are occurring might be different in other galaxies?

  2. ESA Exile says:

    I’m only an amateur but isn’t the difference between type I and type II down to the presence of visible hydrogen spectra (Balmer series) in the type II indicating the presence of stellar outer layers and thus implying it to be a core collapse of a massive star? Type I has no hydrogen and so should be a stellar remnant; a white dwarf (or maybe two?). There are of course sub-species of each general type.

    How a white dwarf actually manages to reach the Chandrasekhar limit without first losing mass in a simple nova has always been a bit of a mystery to me. The main point of the article though is that the two proposed forms of type Ia SN might well have similar visible spectra and light curves but be distinguished by their X-ray spectra. The merger option would also have a different (and variable) luminosity. The problem then follows that that makes them unreliable as standard candles, or have I got it wrong?

  3. Hon. Salacious B. Crumb says:

    ESA Exile said;

    “How a white dwarf actually manages to reach the Chandrasekhar limit without first losing mass in a simple nova has always been a bit of a mystery to me.”

    This is easy to explain. All novae are caused by the ignition of the dense outer hydrogen atmosphere surrounding the WD which reaches thermonuclear temperatures and explodes the atmosphere into the surrounding space. This is likely from a close companion feeding hydrogen to the white dwarf or hydrogen filtering from inside the white dwarf.

    Most white dwarfs are in the approximate range of 0.6 up to 1.4 solar masses, so the scenario for reaching the Chandrasekhar Limit is really a special, and much rarer circumstance.

    As for difference between the visual and X-ray spectrum is proportional – I.e. should be a power curve.

    The paper actually did choose 14 gas-poor elliptical galaxies looking in the 0.3 to 0.7 keV band to “…optimized to detect soft emission from thermonuclear-burning on the surface of an accreting white dwarf.” Based on the numbers of soft resolved X-rays from such nuclear-burning WD sources, this set the “…upper limit on the luminosity of WDs can be obtained.

    So sure. The number of SNIa is likely is this investigation from WD mergers, but is this because of a fundamental aspect of the ratio of WDs by accretion / mergers or something else. Common sense suggest elliptical gas-poor galaxies might favour white dwarf merging as they contain far fewer companion stars able to feed the accretion disks. Ergo, we cannot say galactic SNIa rates are the same as in this investigation.

  4. Excalibur says:

    @Crumb

    The article says:
    “So, for example, the Chandra image above would be about 40 times brighter than observed if Type Ia supernova in the bulge of this galaxy were triggered by material from a normal star falling onto a white dwarf star. Similar results for five elliptical galaxies were found.”

    Seems quite clear to me that they have modelled the x-ray emission _prior_ to any actual SNIa using the two different scenarios. 1) SNIa are caused by merging binary WD, and… 2) SNIa are caused by slow accretion pushing a single WD over the chandrasekhar limit.

    Accretion scenario (2) as modelled would (as i read it) show more overall x-rays by a factor about 30-50x than is actually observed, thus they favor scenario (1).

  5. Hon. Salacious B. Crumb says:

    @ Excalibur

    Yes. I read that too.

    My point is; It could also mean, for example, that SNIa of that scenario might not be as common in elliptical galaxies, or that the proportion of “merging binary WD” to “accretion WD” to for SNIa might be different for some reason.

    Open statements like;

    “Type Ia supernovae serve as cosmic mile markers to measure expansion of the universe. Because they can be seen at large distances, and they follow a reliable pattern of brightness. However, until now, scientists have been unsure what actually causes the explosions.”

    This is not true. BOTH scenarios are known to work, and we do know why!

    The other question of course follows… If the X-Rays are actually “30-50x than is actually observed”, then logically the difference between X-ray emissions in the two SNIa scenarios would be true for observed extragalactic supernova too. As far as I know, there is NO difference is energy output between SN Ia (or SNI) – hence holding them to standard candles.

    Hence the article conclusion stating;

    “Because white dwarfs can come in a range of masses, the merger of two could result in explosions that vary somewhat in brightness.”

    There is also no evidence for this statement.

    Note: Interestingly most WD merger would have to be greater than 0.72 solar mass teach to exceed the 1.44 solar mass to cause the SNIa explosion. However, they could not be greater than about 1.1 solar mass each as the merger could form a neutron star. Furthermore, the formation of the white dwarfs would have to occur about the same time (hence being very similar in mass), else the mass loss to the close stellar companion would be significantly influenced by the first to convert to a white dwarf.
    As the range is fairly narrow (0.72-1.1 solar masses) from the binary scenario when compared to all WD (0.6 to 1.4 solar masses) – leaving stars above 1.2 solar masses with stellar companions feeding mass to an accretion disk. The argument would be something like – heavy white dwarfs are much rarer than binary small white dwarfs – hence more SNia’s will be made by WD mergers.

    *Comment: FK Coma Berenices variable stars are examples of probable stellar mergers, whose ellipsoidal envelopes are/ have merged together, and often show very fast rotation.

  6. LS says:

    According to Mario Livio, very few elliptical galaxy Type 1a SNs are used in Dark Energy studies, so this research doesn’t really say much about the accuracy of such. It will be very interesting to see their future results from the disks of spiral galaxies…

  7. Excalibur says:

    @Crumb

    “The other question of course follows… If the X-Rays are actually “30-50x than is actually observed”, then logically the difference between X-ray emissions in the two SNIa scenarios would be true for observed extragalactic supernova too. As far as I know, there is NO difference is energy output between SN Ia (or SNI) – hence holding them to standard candles.”

    This is where you loose me, the article doesnt talk about the x-ray emission from an actual SNIa, and you are correct in that there is no expected big difference between the two scenarios regarding the output of x-rays _after_ the explosion.

    But there is different expectations _prior_ to the explosion, as in how much x-rays would be expected for a sufficient population of scenario (1) or (2).

    As for mass ranges, first of all it ofc doesnt have to be 2 WD of equal mass so the limits only occur for the pair, and for the upper masslimits orbital motion and deflagration point are very important factors, as it is the deflagration that counters the collapse in the first place. SNIa have what corecollapse SN dont have, they have sufficient fuel to unbind the star(s) completely. I dont know if there is a way to determine this except in simulations, but 2 WD orbiting very closely will either grace eachother (that should set off the deflagration) or one of the WD will be gravitationally disrupted and mass transferred over. The deflagration is what signifies a SNIa, and it is possible that there exists a subclass (not convincingly detected) of SN where the progenitor (or one of its progenitors) are a magnesium WD. The deflagration not being sufficient to unbind the star, and thus cannot halt the collapse, it creates a neutronstar although all the other parameters are the same as for a SNIa. Bit offtopic, but making the point that the pair is harder to analyse as such than just putting (uncertain) limits.

    Even a 0.6+1.4 Msun merger would be a possibility according to the limits you stated.

  8. Lawrence B. Crowell says:

    A supernova due to white dwarf merger would seem to be a physically different form. An SN1 has a fairly strict relative luminosity determined by luminosity and distance. This I have thought is set by the Chandreshanker limit. A merger would seem to negate that “rule.”

    LC

  9. RUF says:

    I still don’t understand how Type Ia’s can be used as standard-candles when Type Ia’s are not standard at all.

    The whole idea of accelerating expansion and dark matter is based on data that we think we understand, but we may be trying to “standardize” something that may be wildly variable.

  10. Aodhhan says:

    The fact of Type1a SN being labeled as “standard candles” never meant each one gave off the ‘exact’ amount of energy as another, every time (One reason they are never used for really great distances now). Yet the 1aSN which gives off energy due to accretion from a star, were close enough to create a standard range which was good enough…so to speak. For looking back billions of years, redshifting is a better measurement.

    Before this study, it was assumed the majority of 1aSN were those which accreted energy from stars (possibly based on the fact, many stars are binary; and they can often go SN more than once… having a longer lifetime). So in many instances, when a 1aSN exploded in a very distant area, it was likely to be the accretion variety.

    Now we are finding out we can no longer assume which type of 1aSN it is. Since the 1aSN which are caused from two white dwarfs colliding are more common and more variable than their accreting cousins.

    It is also easier to determine the mass of a white dwarf accreting energy from a known type of star, than it is to figure out the mass and total energy two colliding white dwarfs will release…. if you even happen to see them before they collide, which isn’t likely.
    In fact, until the 1aSN goes off, we likely didn’t know about the two locked white dwarfs.

    So, knowing 1aSN are more variable than thought, it is more likely to have two white dwarfs collide, along with the fact we won’t know it happens until it does in most cases, really puts a cramp in using 1aSN as standard candles for measuring GREAT distances. For shorter distances, it will likely be fine; since we are likely to have a good idea of the variables for those which repeat and are close neighbors.

  11. Jon Hanford says:

    Some very interesting commentary on this story. I noticed a preprint of this paper by Bogdan and Gilfanov was posted today at arXiv.org: http://arxiv.org/PS_cache/arxiv/pdf/1002/1002.3353v1.pdf

  12. Lawrence B. Crowell says:

    As the article states there is significantly less X-ray production. This means there is a distinction between SN1 due to accretion of gas from a stellar partner and from a merger. Of course a spacecraft is required to monitor these to measure X-ray flux.

    LC

  13. Hon. Salacious B. Crumb says:

    Some interesting comments and good points here;

    Excaliber said; “Even a 0.6+1.4 Msun merger would be a possibility according to the limits you stated.”

    Unlikely such a scenario would occur. Much of the problem is to do with stellar evolution, where two stars are formed in close proximity. (under about 3 radii) this constrains the masses somewhat allowing little variation between them.
    Proximity when the stars turn into white dwarfs can then have mass transfer of their mutual envelopes, than can change the overall mass of the core slightly

    You might like to consider reading a fairly general article on this subject being Iben’s 1985 paper;
    “The life and times of an intermediate mass star – In isolation/in a close binary”
    Especially of note is from pg.30 onwards, the figures on pg.31 and 33.

    Much work has been advanced in the topic on close binaries and the restrictions.

    You also oddly mention “magnesium WDs” I assume you mean Oxygen-Neon (ONe) white dwarfs which are the heaviest WDs possible. (The reason is the heavier elements in the heaviest element sink while the outer atmosphere or surface is mostly the lightest materials which rise to the top. Magnesium is found in such WD, but are only in trace amounts – an offshoot if you like of the various man stages of nucleosynthesis.
    Most merging white dwarfs are in the 0.7 to 0.8 range, and are expected nearly always to be CO (Carbon-Oxygen WD).

    Note : By “deflagration” I assume you mean “detonation”. You sound like you have served in the armed forces at one time or another??

  14. Hon. Salacious B. Crumb says:

    Note: The Iben paper above has a more expanded and more complex version ; entitled

    <A HREF="http://adsabs.harvard.edu/abs/1985ApJS…58..661I" "On the evolution of close binaries with components of initial mass between 3 solar masses and 12 solar masses"

    Again, some of this is already surpassed, but it gives a very good overview for more detailed study or understanding of the topic.

  15. Hon. Salacious B. Crumb says:

    “On the evolution of close binaries with components of initial mass between 3 solar masses and 12 solar masses.”

    Gee, I wish there was some intermediate editor here to see how the submissions look!

  16. Hon. Salacious B. Crumb says:

    Aodhhan said:

    “The fact of Type1a SN being labeled as “standard candles” never meant each one gave off the ‘exact’ amount of energy as another, every time (One reason they are never used for really great distances now).

    Yes, SNIa DO vary in output. The variation is not huge but is significant. The “standard candles” is actually based on the light-curve, which gives the luminosity of the event. Once the absolute magnitude is known, this of course gives the distance.
    In the end, knowing the mean maxima supernovae of all types, can be used to give distance with an error – being often much better than other means.

    Yet the 1aSN which gives off energy due to accretion from a star, were close enough to create a standard range which was good enough…so to speak.

    No quite true. There is little difference between outputs by SNIa either by close binaries or accretion. The energies released is only the equivalent of 1.4 Solar masses (actually 1.44) – and not smaller or larger than this. Two merging white dwarfs of say 0.8 and 0.8 solar masses create just a 1.4 detonation not a 1.6 detonation. Why? The initial collapse shrinks the earth-sized WD to a 5km. neutron star size, then detonates the core and bounces.

    Before this study, it was assumed the majority of 1aSN were those which accreted energy from stars (possibly based on the fact, many stars are binary; and they can often go SN more than once… having a longer lifetime). So in many instances, when a 1aSN exploded in a very distant area, it was likely to be the accretion variety.

    Eh? We can only say that the galaxies (all ellipticals) they have studied seem to be devoid of accretion white dwarfs and favour binary ones. It does not necessarily applies to spirals. Also all supernova can only go once, never twice. (I think you are confusing these the with recurrent nova)

    Now we are finding out we can no longer assume which type of 1aSN it is. Since the 1aSN which are caused from two white dwarfs colliding are more common and more variable than their accreting cousins.

    Again see comment above. We cannot conclude this at all, as the study is only into elliptical galaxies which are mostly devoid of gas. It cannot be concluded this to be true for spirals galaxies, for example.

    It is also easier to determine the mass of a white dwarf accreting energy from a known type of star, than it is to figure out the mass and total energy two colliding white dwarfs will release…. if you even happen to see them before they collide, which isn’t likely.

    Again absolutely not true. The energy released is in the same order of magnitude, where the energy from 1.4(4) solar masses is released. The total amount of energy (luminosity) is derived from the light curve. Most SNI and II are never observed at maximum light, and are often found during the decline in brightness. Therefore luminosity is taken from the shape of the curve. Furthermore, supernova types are determined by they spectra.

    >So, knowing 1aSN are more variable than thought, it is more likely to have two white dwarfs collide, along with the fact we won’t know it happens until it does in most cases, really puts a cramp in using 1aSN as standard candles for measuring GREAT distances. For shorter distances, it will likely be fine; since we are likely to have a good idea of the variables for those which repeat and are close neighbors.

    Really, none of what you say here is true. In fact the biggest problem with SNIa s that they are unlikely to be observed at great distances. The reasoning is the stars have to have sufficient time to go through their evolution and then have enough time to merge.

    Frankly, I do suggest you read the references I’ve given above, and some general text on supernova and someting of the basics on stellar evolution theory.

    Note: It is written as “SNIa” not 1aSN. The “1” is in fact the Roman numeral ‘I”, not the number “1” as against SNII (Supernova Type II) not as SN2″

  17. Lawrence B. Crowell says:

    @ Hon. Salacious B. Crumb: What you indicate appears to depend upon some fairly complicated astrophysics. A merger of two white dwarfs, say both M = 1M_sol, but where the fusion is initiated with the 1.4M_sol coalescence point seems to involve to complicated nonequilibrium conditions. After all the Chandrashekhar limit is computed for degenerate electron pressure in a stationary or equilibrium state. The accretion of matter by the white dwarf is treated as an adiabatic process, not some rapidly process with shock waves and so forth. If the fusion is initiated at the 1.4M_sol coalescence point for all conditions this would appear to represent considerable progress in this sort of astrophysics. If this is so then SNI from white dwarf collapse should still more or less serve as a standard candle — which is my primary interest in the matter.

    LC

  18. Aodhhan says:

    Crumb….

    What I said is on. If you are using outdated information, this is your own ignorance.

    This is the problem between someone who actually has their own information, and someone who attempts to interpret others work. You get half of it and misinterpret the rest.

  19. Excalibur says:

    @Crumb:

    Agreed that it will be unlikely with 0.6+1.4Msun mergers, but at the same time it will be more unlikely with 1.1+1.1 mergers than it will be with 0.75+0.75Msun mergers, and possibly even with 0.65+0.8Msun mergers. Even while evolutionary mechanism favors similary weighted WD, that still does not have with the original article to do, that you where objecting about.

    oxygen-neon-magnesium white dwarf would be the correct full term, sorry for being to lazy to type all that out. I didnt realise it would become an issue to you.

    Afaik Deflagration versus Detonation discussion have not settled yet, but i can be wrong. Are you telling me it is definitely a Detonation ?

  20. Hon. Salacious B. Crumb says:

    Aodhhan said;

    What I said is on. If you are using outdated information, this is your own ignorance.
    This is the problem between someone who actually has their own information, and someone who attempts to interpret others work. You get half of it and misinterpret the rest.

    Your own here ignorance is no excuse. If read what I said, I did say that “Much work has been advanced in the topic on close binaries and the restrictions.” Most of Iben’s 1985 paper, that I highlighted, actually still hold true.
    The only reason why I posted it is that it explains the basics on stellar evolution, and may guide others to understand the topic a little better.
    As for your continued lame attacks on what I present, well really who cares. Clearly it is your own comprehension on science and how it works need to learnt or possibly be brushed up on. After reading your responses here, your knowledge on general stellar evolution is obviously lacking somewhat. Just by sillily writing “1aSN” says it all!

    However, there is one other important point that probably really needs to be clarified here – stems from a misinterpretation from the previous brutal encounters with Anaconda and the EU lot. Here these individuals were all actually attacked and berated on producing old out of date papers from Perratt, Alfen, etc. The issue at the time was not really that of the content of these papers, but their ideas expressed by these authors haven’t been built upon, and more recent knowledge shows these views are mostly incorrect.
    In the case of the articles of Iben here, most of what he states is still part of theory, that has been greatly expanded upon in recent years. Much of what we know about SNI comes from observation of spectra and light-curves of many events. I.e. The actual accretion model, for example was formulated in 1973. The binary star one a few years later.
    As of right now both these models are still plausible and still do meet most expectations and predictions of standard adopted theory. A paper like this one just adds another likely chink in the story, but it does not just automatically supplant the accumulation of all previous knowledge.
    Clearly this work in this story still has holes – and some very big ones. I.e. The sample is only derived in elliptical galaxies, which were selected because they don’t have lots of hot gas. So the question remains: Is this a selection effect or common place in all galaxies? Even the authors admit more work has to be done; I.e. “Now this path to supernovae will have to be investigated in more detail.” In fact this avenue might lead to new understanding of these catastrophic events, it also might be a dead end.

    NOTE: So if you really think, say, Iben here is “out of date”, then you should explain why? (Just openly saying it does not make so.)

  21. Hon. Salacious B. Crumb says:

    Excalibur said;

    Agreed that it will be unlikely with 0.6+1.4Msun mergers, but at the same time it will be more unlikely with 1.1+1.1 mergers than it will be with 0.75+0.75Msun mergers, and possibly even with 0.65+0.8Msun mergers. Even while evolutionary mechanism favors similary weighted WD, that still does not have with the original article to do, that you where objecting about.

    You point here is quite valid. However, it is relevant to the discussion because of the stated misunderstanding of what “merging white dwarfs” actually means. Really I have only brought up the issue of the differences in he masses of the WD stars, because of the generally wrong assumption that they could be of any mass combinations.
    ————————

    …but to clarify. The masses observed of course depend on the nature of the system itself. The reasoning behind the mass constraints is that the progenitor stars must be close enough so that when they convert into WDs the orbit can degrade enough so that they can merge together and form a SNIa. This maximum distance is calculated to be up to about 3 stellar radii, and this in turn means the stars will have a set maximum mass. (Any bigger, and the stars would have to be larger than the limit of 3 radii)

    The second reason why more massive WD are less likely is that massive stars are more rarer than less massive stars. Hence, 1.1 SolMass WD duos are less likely than 0.8 SolMas duos. (We can also know this from eclipsing binaries. There are many examples of the W UMa eclipsing binary variables, whose masses are >0.6 solar masses and if merged, probably forming the R Corona Borealis variables, and are never massive enough when combined to form a SNIa.

    A third point to raise is how WD merge together. They do not crash into each other, so to speak, like two solid objects I.e. like round Billiard or Pool balls. When they approach each other they form “The heavy disk phase” becoming into a Neptune-sized single-like object with heavy ring (something like an a double yoke egg or chocolate with a double cream centre, as my astronomy lecturer once described.) For me it is like a single ravioli, whose centre contains the two WD and the edges of the paste the outlying heavy ring. (Saturn on steroids!)
    The surfaces of the white dwarfs merge together until the 1.4 SolMass Chandrashekhar limit is reached, where is WDs collapses and forms into the SNIa.

    oxygen-neon-magnesium white dwarf would be the correct full term, sorry for being to lazy to type all that out. I didnt realise it would become an issue to you.

    I think you misconstrued my point, and I meany absolutely no criticism of you. (Sorry if I gave that impression) So actually it is no issue at all.

    Note: Several sources (including Wikipedia) have also made this same statement about magnesium too. In the literature most refer to ONe WD, mostly (I think) just to distinguish between CO (Carbon Oxygen) and He WD (Helium.) [I.e. See Figure 19 on Page 31 of Iben 1985 QJRAS paper, as I linked for you previously.]

    Afaik Deflagration versus Detonation discussion have not settled yet, but i can be wrong. Are you telling me it is definitely a Detonation

    Same word, similar meaning ;

    Deflagration, meaning; “combustion that propagates through a gas or across the surface of an explosive at subsonic speeds, driven by the transfer of heat”

    Detonation, meaning; “combustion of a substance that is initiated suddenly and propagates extremely rapidly, giving rise to a shock wave.”

    Deflagration is a term used in the US army to destroy munitions (especially mines), hence why I asked about your possible. military association. For most the term is quite interchangeable, however, the word detonation implies the expanding shock wave after the bounce that we see as the consequence of the visible exploding SNIa. The energy comes from the degeneration of the protons and electrons into neutrons.
    In the end, I suppose it comes down to whether you are taking about before or after the SNIa collapse.
    An interesting point, though!

    Cheers

  22. Hon. Salacious B. Crumb says:

    Clearly I must be a complete idiot.

    You make criticism on one article and then, lo and behold, you hear about the same issues elsewhere. I.e. My response was on February 17th, 2010 at 4:08 pm, and the a few others also begin criticising it too.

    Examples include; S&T Site “Supernova Mystery Remains Just That”, as written by Robert Naeye, February 19, 2010

    The first statement by Robert says;

    Whenever I hear a claimed discovery that overturns conventional wisdom on some important aspect of astronomy, my skepticism meter goes on high alert. Such was the case on Wednesday, when I listened to a NASA press conference in which two astronomers based in Germany presented evidence arguing that the most popular model for Type Ia supernovae is incorrect, at least for elliptical galaxies.

    Indeed there does something quite wrong here.

  23. Excalibur says:

    @Crumb:

    Yes my statement about likelyhood of certain mergers were based on the statistical likelyhood of suitable stars. In terms of SNIa being standard candles, worst case scenario there are still limits, and best case scenario the total mass of the merger will not have a significant difference in the total energy output anyway.

    My comment on Deflagration versus Detonation refers to the discussion weather there is a subsonic or a supersonic combustion. You didnt quite answer it, or atleast not in the way i expected.

    1) Deflagration would be the subsonic (but still very quick) combustion of the WD that eventuall lifts degeneracy and expands it violently. This was atleast earlier the proposed mechanism

    2) Detonation would mean the combustion is supersonic (faster than the speed of sound in the degenerate mass), but from earlier discussions this was still expected to halt the collapse.

    3) You talk about a collapse and rebound that sends a supersonic shockwave outwards (hence this would be a detonation aswell)

    Of these 3, are you saying alternative 3) is now the favored one ?

  24. Hon. Salacious B. Crumb says:

    Excalibar

    Ah, the eternal Hillebrandt & Niemeyer problem of 2000 that is cited nearly everywhere. I.e. The definitive paper being “Type Ia Supernova explosion models” (2000)

    Actually both these solutions have there pro and cons and have been debated for many years. The mathematical proofs are really difficult problems.

    A more recent 2010 paper entitled (arXiv 2009 version) “Turbulence in a three-dimensional deflagration model for type Ia supernovae: II. Intermittency and the deflagration-to-detonation transition probability” by Schmidt, W. et.al. discusses this very issue.

    …delayed detonations (see Hillebrandt & Niemeyer 2000, for a review of explosion scenarios) seem to be the the most promising way of modeling the majority of the observed events.

    They conclude;

    Once all numerical challenges are met, quantitative theoretical arguments in favor or against delayed detonations as an explanation for type Ia supernovae will be within reach.”

    To answer your question the deflagration likely is caused during the collapse of the white dwarf in the seven to eight seconds it takes to reach its highest density during the collapse, after which the star detonates when a certain density is reached. ( The Schmidt (2010) paper say at ~10^7 10,000,000 g.cm^-3!!) Some debate has it that the detonation begins during the collapse itself. Other argue it is likely an intermittent process..

    In fact, all three points you give are likely possible in the SNI event, and vary depending on the circumstances inducing the explosion. I.e. This is why it is called the deflagration- to-detonation (DDT) transition. Whilst the differences may appear minor between the accretion and binary models, the way they destroy themselves is far more complicated.

    Note: My apologies for being so flippant to your posts. I was trying to keep the discussion fairly simple. The deeper explanation of supernova Ia is often best to avoid as it leaves to too many debates.
    Truly excellent comments and much food for thought. It is very much appreciated. Cheers!

  25. Lawrence B. Crowell says:

    I am not familiar with the astrophysics of coalescing white dwarfs, but as Crumb points out the scenario it appears to be a comparatively “gentle” process. In other words the sort of adiabatic approximation used for an accreting WD is possibly more or less valid. Hence these variants of SNIs should be at least similar to the standard model of SNIs. I can’t comment on the relative frequency of these events, but I suspect they are a minority.

    LC

  26. Jon Hanford says:

    Perhaps professional opinion should be sought in this matter.

    Individual Researchers: Supernovae

    * Dr. A. Alberdi (Valéncia)
    * Prof. J.M. Blondin (NCSU)
    * Prof. E. Baron (Oklahoma)
    * Prof. D. Branch (Oklahoma)
    * Prof. S. Bruenn (Florida Atlantic University)
    * Prof. A. Burrows (Arizona)
    * Prof. R. Chevalier (Virginia)
    * Prof. J. Cowan (Oklahoma)
    * Prof. Robert Fesen, and here, too (Dartmouth)
    * Dr. B. Gaensler (MIT)
    * Prof. Mike Guidry (Tennessee and ORNL)
    * M. Hamuy (Carnegie Observatories)
    * Prof. W. Herbst (Wesleyan/VVO)
    * Dr. M. Herant (LANL)
    * Prof. C. Hogan (Washington)
    * Dr. David Jeffery (ORNL)
    * Wayne Johnson’s Mr. Galaxy’s Supernovae
    * László Kiss (JATE University)
    * K. Krisciunas (Washington)
    * Prof. J.M. Lattimer (SUNY-SB)
    * Prof. R. McCray (JILA/Colorado)
    * Dr. Anthony Mezzacappa (ORNL)
    * Dr. P. Nugent (LBL)
    * Dr. Juha Peltoniemi’s Supernova Neutrino Page (U. of Helsinki)
    * Dr. M. Phillips (Las Campanas Observatory)
    * Prof. S. Pineault (Laval)
    * Dr. P. Plait (GSFC)
    # Dr. M. Richmond (Rochester Inst. of Technology) and his list of SNe since 1989
    # Dr. Eduardo Ros Ibarra (MPIfR, Bonn)
    # Dr. P. Ruiz-LaPuente (Barcelona)
    # Dr. S. Ryder (UKIRT)
    # Dr. B. Schmidt (MSSSO)

    * L. Germany (MSSSO)

    # Prof. C. Stubbs (Washington)
    # Prof. P.G. Sutherland (McMaster University)
    # Dr. N. Suntzeff (CTIO)
    # Prof. F.D. Swesty (Stonybrook)
    # Dr. M. Pérez Torres (València)
    # Dr. S. Van Dyk (IPAC)
    # Prof. R.V. Wagoner (Stanford)
    # Dr. K. Weiler (Naval Research Laboratory)
    # Prof. S. Woosley (UC Santa Cruz)

    among others……. :)

  27. Hon. Salacious B. Crumb says:

    @ Jon
    Nice list.

    However, if you had your chance, what would you want to ask them?

  28. Jon Hanford says:

    First off, how independent, peer-reviewed research by you and others compares to that of researchers with many years in the field (experimentalists, theorists, and alike).

  29. DrFlimmer says:

    @ Jon Hanford

    If I were on that list, I wouldn’t understand the question 😉

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