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qraal
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Hi All
Is it type Ia supernovae that detonate in a fusion explosion?
Is it type Ia supernovae that detonate in a fusion explosion?
qraal said:Hi All
Is it type Ia supernovae that detonate in a fusion explosion?
marcus said:Yes, it is type Ia.
Arch2008 said:http://www.astronomynow.com/news/n1003/17supernova/
http://www.sciencedaily.com/releases/2010/03/100315162049.htm
http://www.physorg.com/news182077672.html
http://www.scientificamerican.com/article.cfm?id=type-ia-mergers
http://arxiv.org/abs/1002.3359
White dwarf (WD) stars are key to Type Ia SN. Either WD stars accrete hydrogen from larger companion stars or merge with neutron stars or black holes in computer models that mimic observations. However, several recent events indicate a WD-WD merger as a new explanation. The spectra of these SN show carbon and oxygen (the components of WDs), but not hydrogen from a companion. Apparently, we didn’t have the math to model these mergers, so they were excluded…until now. However, this discovery should not affect the use of Type Ia SN as standard candles or there use in determining the expansion of the universe.
Interesting point... perhaps the answer may lie in the class of WD maybe naturally oxygen-neon-magnesium WD tend to exist incredibly low?Chronos said:If it is simply a matter of accreting enough mass to reach the Chandrasekhar limit, it is curious why they are so rare. A white dwarf siphoning mass from a red giant companion in close orbit would seemingly reach the Chandrasekhar limit in a relatively short period of time and such systems should not be extremely rare. So why are SnIa so rare, or - to paraphrase Fermi - where are they?
In arXiv:0910.1288 129 white dwarfs are identified within 20 pc. In an earlier paper by Holberg, the fraction that are members of binary systems was about 25%. The number of white dwarfs in the Milky Way has been estimated to be around 12 billion [arXiv:0903.2159]. Infering about 25% are members of binary systems, about 3 billion such stars exist. Per http://articles.adsabs.harvard.edu/full/2007MNRAS.375.1315K at least 1% are in the 1.3 solar mass range - meaning around 10 million such stars should exist. Given that no SnIa within our galaxy have been observed in at least 400 years, the maximum accretion rate for any of the 10 million candidate stars could not have exceeded about .0004 solar masses per year over the past 400 years. That seems quite low.
Is it possible that the problem there is, the 25% binary fraction refers to binaries of all orbital separations, whereas mass transfer requires a binary separation not much more than about 1 AU? Maybe the vast majority of the binaries have separations larger than 1 AU. That would seem a little surprising though, I wasn't aware that binary interactions would be so rare.Chronos said:In an earlier paper by Holberg, the fraction that are members of binary systems was about 25%. The number of white dwarfs in the Milky Way has been estimated to be around 12 billion [arXiv:0903.2159]. Infering about 25% are members of binary systems, about 3 billion such stars exist. Per http://articles.adsabs.harvard.edu/full/2007MNRAS.375.1315K at least 1% are in the 1.3 solar mass range - meaning around 10 million such stars should exist. Given that no SnIa within our galaxy have been observed in at least 400 years, the maximum accretion rate for any of the 10 million candidate stars could not have exceeded about .0004 solar masses per year over the past 400 years. That seems quite low.
Ken G said:Remarkable that so little is known about even the most basic attributes of the environment in the type of supernova so central to the "precision cosmology" that brought us dark energy and the accelerating expansion!
Perhaps this will partially answer the questions - "A massive supernova variety - Type Ia - brightens and dims so predictably that astronomers use them to measure the universe's expansion -called a "standard candle."" But this doesn't address the cause, but only the effect.Ken G said:But how can the modeling be telling us that they are good standard candles if we don't know if we should be modeling WD-WD or WD-RG systems? And how can we have empirical evidence they are standard candles if cosmologically old ones could be different from the ones we get independent checks on?
That is a well-written article. I note it raises the same objection I did above, in terms of the problems in arguing that absence of X-rays adjudicates between WD-WD and WD-RG: "Since both scenarios - an accretion-driven explosion and a merger-driven explosion - involve accretion and fusion at some point, the lack of super-soft X-ray sources would seem to rule out both types of progenitor." So much for the WD-WD claim. Still, that article focuses on the "missing progenitor" problem, more so than the "how can we know how bright cosmologically old versions of these things would be if we don't even know what they are" issue.Astronuc said:Perhaps this will partially answer the questions - "A massive supernova variety - Type Ia - brightens and dims so predictably that astronomers use them to measure the universe's expansion -called a "standard candle."" But this doesn't address the cause, but only the effect.
http://www.dailygalaxy.com/my_weblog/2011/02/type-ia-supernova-one-of-the-great-unsolved-mysteries-in-astronomy-.html
Ken G said:I don't actually know what evidence there is that cosmological evolution of type Ia's is not possible,
see also - http://stupendous.rit.edu/richmond/answers/historical.htmlOnly two supernovae have been discovered in other galaxies of the Local Group: SN 1885 or S Andromedae in the Andromeda Galaxy M31, and SN 1987A in the Large Magellanic Cloud.
Absolutely. The problem now is that the SNIa's are the standard ruler, so can't be checked by a standard ruler. There is some X-ray data that was consistent with the SNIa interpretations, but it's not clear how standalone that X-ray data really is-- could be a kind of bandwagon effect. It is certainly true that constant-magnitude SNIa's form part of an overall observationally consistent picture, but it involves dark energy. One can't help wonder if it happened that some new interpretation of the SNIa data implied a different expansion history, then it might need to be made consistent with the other observations by invoking some similarly unknown new physics. But dark energy is certainly the only game in town that succeeds in marrying all the current interpretations.Garth said:If the standard candle and the standard ruler (or whatever) measures of the SNIa's distance are both consistent with the LCDM model then that would be a strong verification that their absolute magnitudes are constant and the model is correct.
And note that one of them, 1987A, occurred in a progenitor that at the time was not even known to be susceptible to going supernova! It seems that every time we get a nearby supernova, we find out something new about supernovae progenitors, and that might be true for the next nearby Ia also. One can't help wondering how supernova physics might change in the next few decades, and what the cosmological consequences might be.Astronuc said:This highlights the difficulty associated with observing SN in fine detail, i.e., being able to observe the progenitor and it's mate:
http://seds.org/messier/more/mw_sn.html
Speaking of which,Ken G said:And note that one of them, 1987A, occurred in a progenitor that at the time was not even known to be susceptible to going supernova! It seems that every time we get a nearby supernova, we find out something new about supernovae progenitors, and that might be true for the next nearby Ia also. One can't help wondering how supernova physics might change in the next few decades, and what the cosmological consequences might be.
http://arxiv.org/abs/astro-ph/0611033SN 1987A was classified as a Type II supernova (SN II) in view of the strong hydrogen lines in its optical spectrum, but because it was the explosion of a blue supergiant (BSG) rather than a red one (RSG), it was an atypical SN II: its light curve did not reach maximum until three months after core collapse and at maximum it was only about 10 percent as luminous as most SNe II.
Neutron stars do have mass limits, usually between 2 and 3 solar masses, and would collapse if they exceeded that limit. But they wouldn't make Ia SNs, because they would look like a bare core collapse (no envelope to blow off), and would not have time to do what would have to be done to those neutrons to get them to fuse. The collapse time would be less than a second once the mass limit was exceeded, so it would just fall right into a black hole, I imagine without much ado, beyond a burst of X-rays from the accretion disk.Chronos said:Anyways, I wonder why WD's are the usual suspects in Ia events. Has any consideration been given to neutron stars as possible Ia progenitors? The mass range of neutron stars vary widely - from less than a solar mass [4U1656+35] to 2 solar masses [PSR J1614-2230]. Do they have 'critical' mass limits? What happens when whatever mass limits they may have is exceeded?
Chronos said:We should limit discussion to Ia supernova. Type II supernova are core collapse events occurring in massive stars - not the detonation event believed responsible for Ia supernova. Anyways, I wonder why WD's are the usual suspects in Ia events. Has any consideration been given to neutron stars as possible Ia progenitors? The mass range of neutron stars vary widely - from less than a solar mass [4U1656+35] to 2 solar masses [PSR J1614-2230]. Do they have 'critical' mass limits? What happens when whatever mass limits they may have is exceeded?
A Type Ia supernova is a type of stellar explosion that occurs in a binary star system, where one star is a white dwarf and the other is a main sequence star. The white dwarf accretes matter from the main sequence star until it reaches a critical mass, triggering a runaway nuclear fusion reaction and resulting in a powerful explosion.
Type Ia supernovae are characterized by their lack of hydrogen and helium in their spectra, as well as their consistent peak brightness. Other types of supernovae, such as Type II, have hydrogen and helium in their spectra and can vary in peak brightness.
A Type Ia supernova occurs when a white dwarf reaches a critical mass, known as the Chandrasekhar limit, which is approximately 1.4 times the mass of the Sun. At this point, the white dwarf can no longer support its own weight, triggering a runaway fusion reaction that results in a powerful explosion.
Scientists study Type Ia supernovae by observing their light curves, which show the change in brightness over time. They also analyze the spectra of the supernovae to determine their composition and use computer simulations to model the explosion process.
Type Ia supernovae are known as "standard candles" because they have a consistent peak brightness, making them useful for measuring distances in the universe. By studying the light from Type Ia supernovae, scientists can determine the expansion rate of the universe and better understand the properties of dark energy, which is thought to be responsible for the accelerating expansion of the universe.