Two paths to a Type Ia supernova?
in [Physics]
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From: Brad Guth on 9 Mar 2010 22:20 On Mar 9, 6:48 pm, Sam Wormley <sworml...(a)gmail.com> wrote: > On 3/9/10 8:34 PM, Brad Guth wrote: > > > > > On Mar 7, 12:20 pm, Sam Wormley<sworml...(a)gmail.com> wrote: > >> On 3/7/10 1:57 PM, Brad Guth wrote: > > >>> I put Sirius B at an original mass of<17e30 kg, Sirius A starting out > >>> at perhaps<7e30 kg and Sirius C which seems gone or near invisible at > >>> perhaps worth something else that's currently down to as little as > >>> 1e29 kg. I also put that original molecular cloud at 1.25e6<1.25e7 > >>> solar masses, and easily parked nearby enough to involve our solar > >>> system. > > >> Based on what observations? > > > Based upon deductive logic, and those crazy seans that are supposedly > > 70+ million years old. Besides, why do you care about the mass of > > Sirius? > > > At less than a tenth the age of our solar system, isn't bigger usually > > better? > > > ~ BG > > Brad, you are not making any sense. Sirius A and B are too far apart > to exchange anything but each other's solar wind. Not far enough, especially when one of those suckers could be worth <1e9 gauss. There's actually an image suggesting a little hydrogen buildup. ~ BG
From: Sam Wormley on 9 Mar 2010 22:25 On 3/9/10 9:20 PM, Brad Guth wrote: > On Mar 9, 6:48 pm, Sam Wormley<sworml...(a)gmail.com> wrote: >> >> Brad, you are not making any sense. Sirius A and B are too far apart >> to exchange anything but each other's solar wind. > > Not far enough, especially when one of those suckers could be worth > <1e9 gauss. There's actually an image suggesting a little hydrogen > buildup. > > ~ BG Where is that image?
From: Steve Willner on 11 Mar 2010 17:32 In article <4b926657(a)news.bnb-lp.com>, Yousuf Khan <bbbl67(a)spammenot.yahoo.com> writes: >But we do have a good model of Type Ia's, maybe not in all of its gory >details, but a good overall picture. All mass-accretion Type Ia's >explode at exactly the same mass level, i.e. when they reach about 1.4 >Solar masses, aka the Chandrasekhar limit. Good overall picture but not a good model. A model is something from which _quantitative_ conclusions can be derived. There is no model for mass accretion supernovae, so far as I know. >Why can't luminosity be independent of mass? Most nuclear fires are >dependent on mass in the universe. It's _plausible_ that luminosity would depend on mass, but that's very far from saying it _must_. Absent a model or observational data, we just don't know. A _plausible_ scenario is that the normal Ia SNe are the accreting white dwarfs and the superluminous Ia's Dan mentioned are white dwarf mergers, but the evidence is not yet in. A big part of science -- perhaps almost a definition -- is keeping track of just what the evidence is for any particular proposition. Some things have very strong evidence for or against, while others have little more than guesses. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 swillner(a)cfa.harvard.edu Cambridge, MA 02138 USA
From: Yousuf Khan on 11 Mar 2010 19:47 Steve Willner wrote: > In article <4b926657(a)news.bnb-lp.com>, > Yousuf Khan <bbbl67(a)spammenot.yahoo.com> writes: >> But we do have a good model of Type Ia's, maybe not in all of its gory >> details, but a good overall picture. All mass-accretion Type Ia's >> explode at exactly the same mass level, i.e. when they reach about 1.4 >> Solar masses, aka the Chandrasekhar limit. > > Good overall picture but not a good model. A model is something from > which _quantitative_ conclusions can be derived. There is no model > for mass accretion supernovae, so far as I know. What quantitative conclusions can't be derived from the model we have now? With what we already have now, we get its luminosity, its mass, its its time duration, and its spectrum. What we don't know yet is a picture of the story inside the core just prior to the explosion. Have I left anything out? >> Why can't luminosity be independent of mass? Most nuclear fires are >> dependent on mass in the universe. > > It's _plausible_ that luminosity would depend on mass, but that's > very far from saying it _must_. Absent a model or observational > data, we just don't know. There are a few types of supernova that produce explosions far weaker or less spectacular than their mass would suggest. For example, Pair-Instability supernovas blow themselves up well before they even get to the helium burning stage, and they leave no neutron star or black hole behind. When they blow up they only leave behind mostly hydrogen and helium. But when it comes to Type Ia, I think we can pretty well say that a bigger mass will result in a bigger blast. > A _plausible_ scenario is that the normal Ia SNe are the accreting > white dwarfs and the superluminous Ia's Dan mentioned are white dwarf > mergers, but the evidence is not yet in. > > A big part of science -- perhaps almost a definition -- is keeping > track of just what the evidence is for any particular proposition. > Some things have very strong evidence for or against, while others > have little more than guesses. I don't disagree that we need more evidence, but I think the only thing that we have to find out is at what limit do two white dwarfs create a Type Ia supernova vs. a neutron star. In the situations where they produce a super-Type Ia supernova, I think there is little doubt that the supernova will be much brighter and bigger than a standard Type Ia. Speaking of which situations produce a supernova or a neutron star. My feeling is that when two white dwarfs of nearly equal mass, that neither one will be able to pull material out of the other one's surface (the degenerate matter equivalent of the Roche Limit). So the two of them will only acquire each other's matter the second that their surfaces touch, and then they will immediately merge. Yousuf Khan
From: Steve Willner on 12 Mar 2010 15:35
In article <4b998f24$1(a)news.bnb-lp.com>, Yousuf Khan <bbbl67(a)spammenot.yahoo.com> writes: >What quantitative conclusions can't be derived from the model we have >now? The dependence of luminosity on mass, for one. >But when it comes to Type Ia, I think we can pretty well say that a >bigger mass will result in a bigger blast. You have yet to give any reason "we" can say any such thing. It could be true, but there is _no evidence_ from either theory or observation so far as I know. There are at least two scenarios consistent with the observation that local SNe Ia are good standard candles: 1. All or nearly all come from accretion onto white dwarfs and therefore all progenitors have the same mass when they explode, giving constant luminosity. 2. Some or all come from white dwarf mergers, and their progenitor masses vary, but there is some regulation or feedback in the explosion process that produces nearly constant luminosity regardless of mass. I know of no evidence to rule out either scenario, but the original observation that started this thread would be more consistent with 2. The dependence of luminosity on stretch might also be more consistent with 2. That's a very long way from saying 2 is correct, of course. The evidence simply doesn't exist. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 swillner(a)cfa.harvard.edu Cambridge, MA 02138 USA |