Two paths to a Type Ia supernova?
in [Physics]
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From: Yousuf Khan on 6 Mar 2010 09:27 Steve Willner wrote: >> Now if there is a secondary type of Type Ia explosion, i.e. the dual >> white dwarf progenitors, then the mass won't be the same between normal >> Type Ia's, since there are now two white dwarfs rather than one. So >> these dual white dwarf supernovas will be much brighter than a normal >> Type Ia > > It's that last statement I keep having trouble with. Why will the > luminosity necessarily be higher if the mass is higher? It could be > that way, of course, but why does it have to be so? As far as I > know, we don't have any good models of Type Ia explosions, and there > isn't any observational knowledge of progenitor masses. So why > couldn't luminosity be independent of mass? 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. That's the reason they are considered such good standard candles, they will always explode at the same size level, and thus their luminosity will remain consistent with each other. Of course, when we refer to "progenitor" in Type Ia's, we're referring to its white dwarf mass, not its mass when it used to be a main sequence star. All white dwarfs are less than 1.4 Solar masses, otherwise they would have become neutron stars. Why can't luminosity be independent of mass? Most nuclear fires are dependent on mass in the universe. Need a bigger nuclear bomb, put more uranium in it. Need a hotter star? Make it bigger. So it would stand to reason that two white dwarfs going supernova at the same time would be a bigger bang than a single white dwarf. Yousuf Khan
From: Brad Guth on 7 Mar 2010 14:57 On Feb 27, 8:17 pm, Sam Wormley <sworml...(a)gmail.com> wrote: > On 2/27/10 9:41 PM, Brad Guth wrote: > > > Sirius(B) is currently gaining mass > > No it's not! "...a large orbital eccentricity carrying them > Sirius A & B] from 31.5 AU apart to 8.1 AU and back again". > > http://stars.astro.illinois.edu/sow/sirius.html > > SIRIUS (Alpha Canis Majoris). From Orion, look south and to the east to > find brilliant Sirius, as if one really needs directions to find the > brightest star in the sky. Its name comes from the Greek word for > "searing" or "scorching," certainly appropriate for a star that shines > at the bright end of the "minus-first" (-1.47) magnitude. Sirius is the > luminary of the constellation Canis Major, the Greater Dog, which > represents Orion's larger hunting dog, and as such is commonly referred > to as the "Dog Star." So great is its prominence that it has two > "announcer stars" that from the mid- northern hemisphere rise before it, > Procyon and Mirzam. Famed from times long past, the first glimpse of > Sirius in dawn announced the rising of the Nile in ancient Egypt. (It no > longer does because of precession, the 26,000-year wobble of the Earth's > axis.) Sirius is also part of a large asterism, the Winter Triangle, the > other two stars of which are Betelgeuse in Orion and Procyon in the > smaller dog, Canis Minor. Because of its brilliance, Sirius is the > champion of all twinklers, the effect caused by variable refraction in > the Earth's atmosphere. The star, a white class A (A1) hydrogen-fusing > dwarf with a temperature of 9880 Kelvin, is bright in part because it is > indeed rather luminous, 26 times more so than the Sun, but mostly > because it is nearby, a mere 8.6 light years away, just double that of > the closest star to the Earth (Alpha Centauri) and the fifth closest > star system. Sirius is "metal rich," its iron content perhaps double > that of the Sun, most likely from some sort of elemental diffusion. With > a radius of 1.75 solar (in agreement with the measured angular diameter) > and a minimum equatorial rotation speed of 16 kilometers per second, > Sirius rotates in under 5.5 days. The star's greatest claim to fame may > be its dim eighth magnitude (8.44) companion, Sirius B, which is > visually nearly 10,000 times fainter than the bright star, Sirius A. > Sirius B, however, is actually the hotter of the two, a blue-white > 24,800 Kelvin. Though typically separated from each other by a few > seconds of arc, Sirius B is terribly difficult to see in the glare of > Sirius A. The only way the companion star can be both hot and dim is to > be small, only 0.92 the size of Earth, the total luminosity (including > its ultraviolet light) just 2.4 percent that of the Sun. The two orbit > each other with a 50.1 year period at an average distance of 19.8 > Astronomical Units, about Uranus's distance from the Sun, a large > orbital eccentricity carrying them from 31.5 AU apart to 8.1 AU and back > again. They were closest in 1994 and will be again in 2044, while they > will be farthest apart in 2019. From the orbit (and spectroscopic data), > we find that Sirius A and B have respective masses of 2.12 and 1.03 > times that of the Sun. Sirius B is the chief member of a trio of classic > white dwarfs, the others Procyon B and 40 Eridani B. Its high mass and > tiny radius lead to an amazing average density of 1.7 metric tons per > cubic centimeter, roughly a sugar cube. White dwarfs are the end > products of ordinary stars like the Sun, tiny remnants that were once > nuclear-fusing cores that have run out of fuel. Most are balls of carbon > and oxygen whose fates are merely to cool forever. To have evolved > first, Sirius B must once have been more massive and luminous than > Sirius A. That its mass is now lower is proof that stars lose > considerable mass as they die. Given the mass of the white dwarf and the > 250 million year age of the system, Sirius B may once have been a hot > class B3-B5 star that could have contained as much as 5 to 7 solar > masses, the star perhaps losing over 80 percent of itself back into > interstellar space through earlier winds. (Thanks to Steve Ash for > prompting a rewrite.) 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. What's the magnetic push/pull of Sirius B and A worth? ~ BG
From: Sam Wormley on 7 Mar 2010 15:20 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?
From: Brad Guth on 9 Mar 2010 21:34 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
From: Sam Wormley on 9 Mar 2010 21:48
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. |