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Astronomers Awaiting 1a Supernova
Aryabhata writes to tell us BBC News is reporting that astronomers have sighted a star on the brink of a "1a" supernova. This opportunity presents the first chance astronomers have ever had to view a supernova of this magnitude up close. From the article: "They are so rare that the last one known in our galaxy was seen in 1572 by the great Danish astronomer Tycho Brahe, who first coined the term nova, for "new star", not realizing he was in fact witnessing the violent end of an unknown star. It has long been believed that type 1a supernovae are the death throes of a white dwarf star. But all modern ones have been so distant that it has not been possible to see what had been there beforehand."
It happened long ago and the light is just now reaching us.
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From TFA:
But soon, RS Oph could pass the tipping point - the nuclear flame will detonate from deep inside the star and blow it apart. How soon is not clear.
"It could be tomorrow, but most likely it'll be 1,000, 10,000, 100,000 years from now," says Jeno Sokoloski.
Wow that's some long life astronomers. I wonder if they will be around to see DNF getting release.
Stupid headline.
version 1a? They aren't even in beta yet!
Monstar L
Rho Casspioiae is supposedly near the brink of explosion, too, and aside from that, I remember hearing about some luminous supergiant or hypergiant expected to explode in the same constellation, Casspioia.
Coincidentally, two other supernovas have ocurred in that area, one of which was the one Tycho Brahe saw. Keep an eye on the hypergiants (see: Wikipedia's explanation of how stars are classified)
That's a NOVA, when the accumulated mass around a white dwarf in a binary system is launched outward, which the star regularly does. This would be a SUPERNOVA, when the white dwarf within the binary system actually explodes from within.
"Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." -- the Hitchhiker's Guide to the Galaxy.
Not only are the distances vast, the times are vast too. Stars live for billions of years. One year in the lifespan of a human is roughly comparable to perhaps 70 million years in the lifespan of a star.
So when someone says "soon" in reference to a prediction of when some stellar event is going to occur, it's likely you'll have to scale up the term by roughly the same amount. "Soon" to a human generally means within/around a day or so, so scaled up to stellar times, that would be within/around 200,000 years.
I expect that by the time this supernova happens, humans will either be unbelievably technologically advanced, or they'll be extinct.
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...that we have observed. The key answer is, that we have observed.
The radius of observation of these kinds of things is substantially smaller than infinite. Especially when you consider that earlier periods had a lower capability of observation.
So, really, we're talking about a fairly finite range of space and time in which supernovas would have to occur for them to be human-observable.
I've never seen a star go supernova before. But if it's anything like my old Chevy Nova, it'll light up the night sky!
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Shit.
So that would be like eating a vindaloo and lighting farts.
Nonono.
That's a nova. You've got a white dwarf, with a red giant companion star. Gas flows from the red giant to the white dwarf, accumulating there. Eventually enough builds up for fusion to begin in that accreted matter, and that causes a great increase in luminosity which we call a nova.
But that accreted mass doesn't disappear. Sure, some of it gets blown out into space, but the 'ash' of the fusion 'burn' accumulates with each cycle. Eventually, enough mass accumulates that the white dwarf star, in which fusion reactions have essentially stopped, becomes massive enough to start fusing the carbon that was created back when it was still on the main sequence.
So you have a sudden wave of carbon fusion that occurs everywhere throughout the star, causing an enormous increase in luminosity and also blowing the star apart. This is, not surprising, referred to as a 'carbon detonation' supernova, or Type 1a supernova, which is what the article was talking about. This thing's right under the critical mass at which that'll happen, so a bit more accumulation of stellar matter from its companion star, and 'boom.'
I'm curious. At what range would a Type 1a supernova be lethal to life on Earth?
As far as the size of the galaxy is concerned, 1,950 light-years is essentially in our back-yard. Keeping with scale, are we talking about a firecracker or a stick of dynamite?
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You are right that you can estimate stellar masses in binary systems by observing the system's orbital period. However, that is only useful for binary systems that are close enough for our telescopes to resolve (visually) the space between them. There are other, non-viusal methods that are used, but you basically have a limit on how far away a binary system can be for it to be observed in this way.
The utility of type 1a supernovae is that they are all produced by white dwarf stars exploding. White dwarfs are roughly earth-sized stellar cores that have no thermonuclear reactions going on inisde - they are the remnants of stars between about 1 and 5 solar masses after the outer layers have been blown off.
The imporant point is that the gravity of the stellar core's mass is not counteracted up by the pressure of the thermonuclear reactions inside. Rather, something called degenerate electron pressure holds the white dwarf up and prevents it from collapsing. Degenerate electron pressure can only counteract gravity for masses up to 1.4 solar masses, meaning that any white dwarf that somehow grows to a mass greater than 1.4 solar masses (usually by grabbing mass from a companion star), it will collapse. The collapse catastrophically increases the pressure inside the white dwarf, re-igniting nuclear fusion, and produces a sudden violent explosion.
Because white dwarfs are all of the same mass when they explode - 1.4 solar masses (the Chandrasekhar (sp?) limit - they are all of roughly the same brightness (>10^9 times as bright as the Sun). Because of this, one only has to see a type 1a supernova to deduce from the apparent brightness the distance from earth to the explosion. If a type 1a supernova occurs inside a cluster of stars, it conveniently tells us the distance from here to that cluster of stars. Because the distances over which supernova can be observed is orders of magnitude greater than most other stellar phenomena, the are essential in determining distances to faraway objects (from 1 to 1000 megaparsecs away (1 parsec = ~3.2 light years)). Distances to other galaxies are determined this way.
They type of supernova being observed can be determined by the specatra of light coming from it. I can't recall the distinguishing characterisitics of type 1a supernova, but suffice it to say they can be distinguished from other types of supernova.
Wikipedia lists ones occuring in our galaxy in 1006, 1054, 1181, 1572, 1604, and I remember from other sources that several were observed during Roman times.
Isn't that typical. Before the telescope, there was a frickin' smorgasboard of supernovae at close range, then no sooner does man invent the telescope and the party's over, which draws me to the conclusion: I blame this supernovae drought on Galileo.
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