Two paths to a Type Ia supernova?
in [Physics]
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From: Steve Willner on 25 Feb 2010 15:40 In article <4b822af5$1(a)news.bnb-lp.com>, Yousuf Khan <bbbl67(a)yahoo.com> writes: YK> If there are enough binary white dwarfs that can merge, I don't think YK> the universe is old enough yet to have seen them yet. It takes a long YK> time to create a white dwarf, let alone two of them together. Stars up to something like 2-4 solar masses produce white dwarfs, and they evolve in something under a billion years. Equal-mass binaries are pretty common, and mass transfer shortens the lifetime of the secondary. I don't think there's an obvious timescale problem, at least at moderate redshift. Of course to get a real answer, one would have to make a quantitative comparison of supernova rates with actual lifetimes and stellar numbers. I certainly haven't done that. YK> if the path to Type Ia's includes merging white dwarfs, then that YK> would mean that using Type Ia's as standard candles is unreliable. Not necessarily. It might turn out, for example, that the visual magnitudes don't much depend on the masses. Nevertheless, having multiple mechanisms would certainly justify some suspicion. There is strong evidence that _local_ type Ia SNe are good standard candles, especially after correction for light curve "stretch." I think the question is whether distant Ia's are the same kinds of objects -- or at least have the same magnitudes -- as the local ones. Stay tuned. On Feb 22, 2:12 am, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: Usually Eric knows what he's writing about, but he seems to have had a bad day here. YK> Common knowledge about what creates a Type Ia supernova is that a white YK> dwarf siphons off matter from a companion star, usually a red giant. It YK> siphons off so much matter that its mass goes over the Chandrasekhar YK> limit (approx. 1.4 solar masses), EG> No. That would mean it does a collapse into a black hole with EG> minimal energy release. Yousuf's statement is correct. Core-collapse supernovae (Type II, for example) may produce black hole remnants, but there is still plenty of energy released. EG> A Type 1a is the surface explosion of accumulated layers of Hydrogen on EG> the surface of a white dwarf. Eric here describes a nova, not a supernova. YK> The second theorized method to Type Ia supernovas is when there are two YK> white dwarfs, and the two of them merge which takes them over the YK> Chandrasekhar limit and blows them both to smithereens too. EG> No. The type of a supernova isn't something that is meaningless, EG> this would be a different (and not known to be seen) type of EG> supernova. The type of a supernova is based on its spectrum and light curve. It's conceivable that different underlying processes could produce the same observed "type." In any case, Yousuf's description is a possible origin for Type 1a SNe. EG> things that reach the Chandrasaekhar limit implode - not explode. Type Ia SNe are thought to leave no remnant; the entire star is destroyed (or both stars, if it was a merger). [Eric: I tried emailing you before posting the above, but the email bounced.] -- 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: Brad Guth on 26 Feb 2010 10:30 On Feb 21, 10:57 pm, Yousuf Khan <bbb...(a)yahoo.com> wrote: > Common knowledge about what creates a Type Ia supernova is that a white > dwarf siphons off matter from a companion star, usually a red giant. It > siphons off so much matter that its mass goes over the Chandrasekhar > limit (approx. 1.4 solar masses), and this creates a thermonuclear > explosion so big that all of the white dwarf's matter gets dispersed > leaving no further core behind. This scenario is known as the "accreting > white dwarf". > > The second theorized method to Type Ia supernovas is when there are two > white dwarfs, and the two of them merge which takes them over the > Chandrasekhar limit and blows them both to smithereens too. One problem > with this is that if a Type Ia is produced this way, then depending on > the mass of the two original white dwarfs, they might be well over the > Chandrasekhar limit and the explosion would be bigger than a regular > Type Ia. Another problem with this theory is that another possible > theoretical path for them is that the two white dwarfs merge to form a > neutron star, instead of blowing up. > > In this article, the researchers say that if most SNIa's are of the > accreting white dwarf type, then there should be a lot of X-rays > produced from the infalling matter prior to the explosion. If it's > merging white dwarfs, then there would be no X-rays produced priorly. > Their studies conclude that there is less X-rays coming out of various > galaxies than can be expected if there were lots of accreting white > dwarfs inside them. I personally think this is way too indirect of an > observation to be conclusive about anything. The article author's > conclusion is pretty much the same. > > If there are enough binary white dwarfs that can merge, I don't think > the universe is old enough yet to have seen them yet. It takes a long > time to create a white dwarf, let alone two of them together. But if the > path to Type Ia's includes merging white dwarfs, then that would mean > that using Type Ia's as standard candles is unreliable. That would > affect distance measurements of Dark Energy in the universe. > > Yousuf Khan > > *** > SkyandTelescope.com - News from Sky & Telescope - Supernova Mystery > Remains Just Thathttp://www.skyandtelescope.com/news/84771852.html Besides Sirius(B) going supernova and taking Sirius(A) out at the same time, Can LHC create a local nova? http://blogs.physicstoday.org/newspicks/2010/02/rhic-finds-hints-to-why-we-exi.html So far, those mostly public funded wizards at LHC are only missing or having lost track of 98% proton mass, and if they keep going and going with this colliding process should create either black holes, hot quark soup or ice-9. How paramagnetic or diamagnetic are these protons? How paramagnetic or diamagnetic are those quarks? With trillions upon trillions of spare/rogue quarks running lose, what could possibly go wrong? ~ BG
From: Yousuf Khan on 27 Feb 2010 12:16 Brad Guth wrote: > Besides Sirius(B) going supernova and taking Sirius(A) out at the same > time, Congrats Brad, this is actually a plausible outcome of the Sirius system, billions of years down the road. After Sirius A goes red giant, it won't be close enough to Sirius B to create a Type Ia supernova through gas accretion. However, it might produce occasional novas on Sirius B, as some small amount of Sirius A's gas might fall on to Sirius B. Eventually, Sirius A will settle down into its own white dwarf retirement. Then tens of billions of years later, the two of them might spiral in close enough to each other to collide and create a dual-white dwarf Type Ia supernova. Yousuf Khan
From: Brad Guth on 27 Feb 2010 22:41 On Feb 27, 9:16 am, Yousuf Khan <bbb...(a)spammenot.yahoo.com> wrote: > Brad Guth wrote: > > Besides Sirius(B) going supernova and taking Sirius(A) out at the same > > time, > > Congrats Brad, this is actually a plausible outcome of the Sirius > system, billions of years down the road. After Sirius A goes red giant, > it won't be close enough to Sirius B to create a Type Ia supernova > through gas accretion. However, it might produce occasional novas on > Sirius B, as some small amount of Sirius A's gas might fall on to Sirius > B. Eventually, Sirius A will settle down into its own white dwarf > retirement. Then tens of billions of years later, the two of them might > spiral in close enough to each other to collide and create a dual-white > dwarf Type Ia supernova. > > Yousuf Khan Sirius(B) is currently gaining mass, so perhaps we got thousands of years at best. ~ BG
From: Yousuf Khan on 27 Feb 2010 23:04
Brad Guth wrote: > On Feb 27, 9:16 am, Yousuf Khan <bbb...(a)spammenot.yahoo.com> wrote: >> Brad Guth wrote: >>> Besides Sirius(B) going supernova and taking Sirius(A) out at the same >>> time, >> Congrats Brad, this is actually a plausible outcome of the Sirius >> system, billions of years down the road. After Sirius A goes red giant, >> it won't be close enough to Sirius B to create a Type Ia supernova >> through gas accretion. However, it might produce occasional novas on >> Sirius B, as some small amount of Sirius A's gas might fall on to Sirius >> B. Eventually, Sirius A will settle down into its own white dwarf >> retirement. Then tens of billions of years later, the two of them might >> spiral in close enough to each other to collide and create a dual-white >> dwarf Type Ia supernova. >> >> Yousuf Khan > > Sirius(B) is currently gaining mass, so perhaps we got thousands of > years at best. No, it's not. Yousuf Khan |