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SN 2011dh

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#1 rookie

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Posted 16 February 2013 - 11:52 PM

I read in January 2013 Astronomy magazine page 19, that SN2011dh was probably a binary with the progenitor, a yellow supergiant undergoing a mass loss to its blue companion.

This paper by Bersten; et al describes this further. The First Evidence that a Yellow SuperGiant Became a SuperNova

the mass-donor star ---the one that eventually explodes---


It is not at all clear to me how mass loss from a supergiant can cause an instability that would lead to a core collapse supernova. In fact, in the conventional (red supergiant) type II supernova scenario, the star’s greatly distended envelope has no influence whatsoever on what’s happening in the core.

How did this happen? Can anyone explain the mechanism? I find this description in other papers, but not the AP dynamics explained.

If there has been a thread discussion about this already, please post the link. I was not able to locate it on my own. Thanks

#2 Ebyl

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Posted 17 February 2013 - 12:34 AM

I think if you could propose a viable mechanism for this, you'd be greatly encouraged to publish as soon as possible. ;) Point being, I'm guessing a lot of astrophysicists are wondering the same thing. While I know they have proposed a model for this with results consistent to the observations, I don't think it will be the end of the discussion on exactly how it happened.

#3 Carl Coker

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Posted 21 February 2013 - 03:00 PM

They don't talk very much about why the star was yellow when it blew up in the paper (I didn't see any significant discussion of it at all when I skimmed it, actually). They give most of their time to arguing that it was a binary, and that the progenitor was an extended object (i.e., a star with nuclear burning in the core as opposed to a degenerate remnant).

If I had to guess why the star was yellow, it's that the companion was siphoning off enough mass for the star to be much smaller than it would have been were it a single star. Since the energy generation in the core would be basically fixed no matter what the extended part of the envelope is doing, as the star gets smaller, the surface gets hotter and bluer. If the star had been alone, it would have exploded as a red supergiant.

#4 GlennLeDrew

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Posted 22 February 2013 - 07:22 PM

Massive stars need not necessarily be in the *red* supergiant phase at the moment of core collapse. Such stars--if of sufficient mass--are believed to re-cross the Cepheid instability strip a couple or more times. The core could conceivably collapse at most any stage of this process.

The presence of the companion may have little impact, at least as far as its 'robbing' of some of the outer envelope of the other star is concerned. The veritable vaccuum of the tenuous envelope has nothing, really, to do with what's going on in the comparatively minute (planet-sized), super-dense core.

#5 Neutrino?

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Posted 22 February 2013 - 07:56 PM

They don't talk very much about why the star was yellow when it blew up in the paper (I didn't see any significant discussion of it at all when I skimmed it, actually). They give most of their time to arguing that it was a binary, and that the progenitor was an extended object (i.e., a star with nuclear burning in the core as opposed to a degenerate remnant).

If I had to guess why the star was yellow, it's that the companion was siphoning off enough mass for the star to be much smaller than it would have been were it a single star. Since the energy generation in the core would be basically fixed no matter what the extended part of the envelope is doing, as the star gets smaller, the surface gets hotter and bluer. If the star had been alone, it would have exploded as a red supergiant.


Yes, that would be why. The whole point of the paper is arguing for the progenitor being a YSG. This goes against some of the other papers mentioned in Discussion 4.2.

#6 Carl Coker

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Posted 23 February 2013 - 12:37 AM

Massive stars need not necessarily be in the *red* supergiant phase at the moment of core collapse. Such stars--if of sufficient mass--are believed to re-cross the Cepheid instability strip a couple or more times. The core could conceivably collapse at most any stage of this process.

The presence of the companion may have little impact, at least as far as its 'robbing' of some of the outer envelope of the other star is concerned. The veritable vaccuum of the tenuous envelope has nothing, really, to do with what's going on in the comparatively minute (planet-sized), super-dense core.


The current consensus on Type II supernovae is that the progenitor stars are either RSG's or blue giants. Back in the 1980's and earlier, it was only thought that RSG's would go supernova (it was a great shock when the progenitor for SN 1987A was found to be a ~20-25 M_sun blue star!). While massive stars can cross the instability strip multiple times during their lives, it is usually thought that they will end it at one extreme or the other of the loops they trace on the HR diagram, as the the time spent on each loop is very short compared to the life of the star. Hence the necessity of arguing that this particular star was, in fact, a YSG.

According to the current understanding, the progenitor of SN 2011dh should have been a RSG when it blew up, as it was not massive enough to blow off its envelope and return to being a blue supergiant. This seems to be the motivation for introducing a companion which was stripping mass from the star and allowing it to remain yellow.

#7 rookie

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Posted 23 February 2013 - 11:42 AM

Thanks for the replies and discussions. It will be interesting to follow the future studies of this event and see if they come to any definate conclusions.

#8 rookie

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Posted 05 April 2013 - 02:50 PM

Discovered Virtual Telescope as a page dedicated to SN 2011dh






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