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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."
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)
They mention the star by name many times in the article. Did you actually read it? They mention it in the first few sentences. Here's the wiki on the star: http://en.wikipedia.org/wiki/RS_Ophiuchi
Actually, they do name the star. It's RS Ophiuchi which is 1,950 light-years from Earth according to the linked Wikipedia article. It's worth a look if you are now thinking of doing some amateur astronomy since it also contains some information on some of the star's past failures at going nova and a bunch of related links.
UNIX? They're not even circumcised! Savages!
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.
The distance is 1,950 -- 5,200 ly, according to Wikipedia. The distance to most stars in this distance range is quite uncertain because it is too far away for today's parallax measurements.
http://en.wikipedia.org/wiki/Supernova#Impact_of_
So, who knows? Hollywood disaster movies might have t right after all!
Why does it matter whether it "already" happened? We cannot know about it or be affected by it until the first photons reach us. If it happened 1000 years ago 1000 light years away, or 100,000 years ago 100,000 lightyears away, or yesterday 1 lightday away, it's still "happening now" as far as we're concerned.
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.'
While this doesn't directly answer your question, you might find the following interesting. Steven Dutch, a professor at the University of Wisconsin at Green Bay has estimated what would happen if the sun were to go supernova. Some highlights: the radiation flux on the daylight side of the earth would be the same as if our entire nuclear arsenal were to go off once per second at a distance of one kilometer. The reflected light from the full moon would be 10,000 times brighter than the sun; Venus would shine six times as intensely as the normal sun. The earth vaporize in a matter of days.
By the way, the sun will never become a supernova. The calculations are illustrative only.
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.
According to Wikipedia, the "serious effects" range for Type Ia supernovae is about 1000 parsecs or 3300 light years. If 1950 light years is the correct distance to RS Ophiuchi, we are in the danger zone. Evidently from above posts & links Rho Cassiopeiae is also on the verge, but it's 8000 to 10,000 light years distant and a "mere" type II supernova candiate, anyway. Rho Cassiopeiae = fireworks display. RS Ophiuchi = hand grenade at least and maybe a 2000 lb bunker-buster. Lots of calculations here.
If you want your life to be different, live it differently.
Suppose we send a signal towards the supernova as soon as we see it explode. Suppose that there is an observer, a really though one, staying close to the supernova as it goes off, who measures the time difference between the supernova explosion and our signal. Suppose that, as soon as he receives our signal, he sends another signal, with this data encoded, towards us. Suppose also, for simplicity, that all observers are at rest relative to each other and the supernova (they aren't really - stars move relative to each other - but that movement is too slow to cause much problems for our experiment).
Now, since light travels at a constant speed, the observer got our signal halfway between us sending it and us receiving the reply. Since both we and him are at rest relative to each other and supernova, we don't get any time dilation, and can use simple math to calculate when the nova exploded. Simply substract the time difference told to us by the other observer from the midpoint between us sending him the signal and receiving a reply. We'll arrive at a point in time somewhere before we observed the nova; whether that point is in the "distant" past or "near" past is a value judgement.
Another way of looking at this is simply understanding that light moves at a finite speed; so, if we observe the light from a distant event, that light was emitted at the moment of the event and took a nonzero time to reach us, and so the event must have happened at a nonzero time in the past.
Haven't you ever heard: the further you look in space, the further back you look in time ?
Or just read the page you linked to. It talks about causal past and future. It doesn't claim that events that we cannot yet observe due to the limited speed of light haven't yet happened, only that we can't be affected by them yet - which is pretty self-obvious, if you think about it a bit.
The Sun could have blown up 4 minutes ago, but we wouldn't know for another 4. It still blew up 4 minutes ago, it simply takes another 4 until this can be observed by us. Of course it's unlikely that the Sun would blow up suddenly, but - hey, what's that ligNO CARRIER.
Not enough, apparently. Which is a great pity, since relativity deals with the basic structure of time and space and the very nature of reality itself. It's utterly fascinating stuff, completely different from endlessly memorizing formulas and using them to calculate how much tension some wire has - that's fine for engineers, but relativity is the "actually, you can build a time machine and warp drive" theory and quantum mechanics are the dreams stuff is made of; that is where physics education should start, to give the student the motivation to go through the grind, knowing where the basics will lead.
Forget magic. Any technology distinguishable from divine power is insufficiently advanced.