What exactly happens to a star about to go supernova?
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Stars spend most of their life fusing hydrogen to helium.  As a star gets near the end of its life it starts to fuse Helium into heavier elements going up to Carbon, Oxygen, Silicon, etc (taking progressively less time to fuse each of them).\n\nEventually the star will have an Iron core but while fusing elements lighter than Iron results in an energy release trying to fuse Iron into something heavier requires energy and so the fusion reaction can not proceed any further.\n\nNow throughout the life a star the star is in a hydrostatic equilibrium between gravity pulling the star together and the radiation pressure from the nuclear fusion pushing the star apart, with the fusion reaction stopping the gravity wins and the star collapses.\n\nThe sudden collapse causes the core to be crushed to very high density at which point protons and electrons combine to form a neutron and a neutrino according to p + e -> n + ν with the neutrino escaping (the neutrinos carry most of the energy).\n\nThe core of the star is now very small and the outer layers fall in and bounce off which is what causes the explosion.\n\nIt takes a couple of hours for the outer layers of the star to actually blow apart (which is what we'd see) so the first evidence that a supernova has occured is the neutrino burst.
994321
I'm afraid it won't explode now.\nIt won't go and explode as a nova or super-nova unless something real bad happens and it gets a denser core.\nOur star won't explode until at least 5 billion years time, unless anything makes it do it.\nThe term nova means very large explosion. But our star won't explode it will widen with a little explosive force and all of it's gaseous surface and mid layers will blow off.\nOur star is an M class (G Medium class) a super-nova will only happen with L class stars (O Large class) + (M Small class) the M and S class have novas only when they collide it is likely to be explosive as the stars are young and hot.\nThe main course of nuclear fusion is:\nD+T=4He+1n or 3-2H+2-1H=4He-3.5MeV+1n-14.1/14.2MeV\nThe sun will not explode in at least 1 billion to 5 billion years!
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Our sun will not supernova.  It will, over a very long time, expand into a relatively small red giant, which will have a diameter greater than the Earth's orbit.\n\nLong before that the Earth will have become far too hot to live on, but the process will be very, very slow -- it'll take over a billion years -- not a giant explosion.\n\nSorry to disappoint you.  I know, you sound like you were looking forward to it.  Funny how many people answering this question think otherwise.  I guess that's the irony of the internet for you.\n\nSee the link below for all the details:
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No, main sequence stars (like our sun) last for about 10 billion years. It has lived for about 5 billion years or so, which means the sun has another 5 billion more years to live. After those 5 billion years are over the fusion process is stopped (due to the lack of hydrogen). The star collapses on itself and makes the star even hotter. All that heat fuses the helium and the star expands into a red giant. It will last in this form for another 100 million years or so. Then the outer layers of the red giant comes of creating a planetary nebula. Then after that gas is gone all that is left is the hot core or the white dwarf. The white dwarf cools and becomes a cold dead core (Black Dwarf)
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...when it has degenerated & becomes dead.\n\nA white dwarf is what stars, like our Sun, become when they have exhausted their nuclear fuel. Near the end of its nuclear burning stage, such a star expels most of its outer material (creating a planetary nebula), until only the hot core remains, which then settles down to become a very hot (T > 100,000K) young white dwarf. Since a white dwarf has no way to keep itself hot unless it is accreting matter from a nearby star (see Cataclysmic Variables), it cools down over the course of the next billion years or so. Many nearby, young white dwarfs have been detected as sources of soft X-rays (i.e. lower-energy X-rays); recently, soft X-ray and extreme ultraviolet observations have become a powerful tool in the study the composition and structure of the thin atmosphere of these stars.\n\nA typical white dwarf is half as massive as the Sun, yet only slightly bigger than the Earth. This makes white dwarfs one of the densest forms of matter, surpassed only by neutron stars.\n\nBecause a white dwarf is no longer able to create internal pressure, gravity unopposedly crushes it down until even the very electrons that make up a white dwarf's atoms are mashed together. In normal circumstances, identical electrons (those with the same "spin") are not allowed to occupy the same energy level. Since there are only two ways an electron can spin, only two electrons can occupy a single energy level. This is what's know in physics as the Pauli Exclusion Principle. And in a normal gas, this isn't a problem; there aren't enough electrons floating around to completely fill up all the energy levels. But in a white dwarf, all of its electrons are forced close together; soon all the energy levels in its atoms are filled up with electrons. Well, if all the energy levels are filled, and it is impossible to put more than two electrons in each level, than our white dwarf has become degenerate. For gravity to compress the white dwarf anymore, it must force electrons where they cannot go. Once a star is degenerate, gravity cannot compress it any more because quantum mechanics tells us there is no more available space to be taken up. So our white dwarf survives, not by internal combustion, but by quantum mechanical principles that prevent its complete collapse.\n\nDegenerate matter has other unusual properties; for example, the more massive a white dwarf is, the smaller it is! This is because the more mass a white dwarf has, the more its electrons must squeeze together to maintain enough outward pressure to support the extra mass. There is a limit on the amount of mass a white dwarf can have, however. It was found by Subrahmanyan Chandrasekhar to be 1.4 times the mass of our Sun, and is is call the "Chandrasekhar limit" after its discoverer. \n\nWith a surface gravity of 100,000 times that of the earth, the atmosphere of a white dwarf is very strange. The heavier atoms in its atmosphere sink and the lighter ones remain at the surface. Some white dwarfs have almost pure hydrogen or helium atmospheres, the lightest of elements. Also, the very strong gravity pulls the atmosphere close around it in a very thin layer, that, if were it on earth, would be lower than the tops of our skyscrapers! \n\nUnderneath the atmosphere of many white dwarfs, scientists think there is a 50 km thick crust, the bottom of which is a crystalline lattice of carbon and oxygen atoms. One might make the comparison between a cool carbon/oxygen white dwarf and a diamond! (After all, a diamond is just crystallized carbon!)
310713
First of all....Are all stars formed from nebulae? If not where do they come from? What happens to a star after they are burned out? Do all stars end up a black hole or supernova? What determines their final destination? Where will our Sun end up when its fuel is spent? What are dwarf stars? \nThus... keeping that in mind...all stars are formed from nebulae (the plural of nebula). Nebula is a term for a cloud of gas, and stars form from gas. Stars more massive than ~ 6 solar masses are expected to supernova, stars less massive than this (like our Sun, of course) become white dwarfs. After a supernova, there may be nothing left, or there could be a remnant: either a neutron star or a blackhole. If the remnant is more massive than around 3 solar masses it will probably end up as a blackhole. Stars are smallest when they are burning hydrogen into helium, which is what stars do during most of their lifetimes. Stars in this stage are sometimes called dwarfs. There are also two other kinds of "dwarfs": white dwarfs are burned-out stars mentioned above (the Learning Center has more info on these), and brown dwarfs are stars which never accumulated enough mass to start burning hydrogen.
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A star takes birth from nebula. Then in the ending years of its life it's volume gets increased and becomes red supergiant. Then it becomes supernova for a few months or years but about 10 billion times as bright as our sun. Then \n1) It can get recycled into nebula OR\n2) It can become a neutron star OR\n3) It can become a black hole.\n\nBlack holes are thought to form from stars or other massive objects if and when they collapse from their own gravity to form an object whose density is infinite: in other words, a singularity. During most of a star's lifetime, nuclear fusion in the core generates electromagnetic radiation, including photons, the particles of light. This radiation exerts an outward pressure that exactly balances the inward pull of gravity caused by the star's mass. \n\nAs the nuclear fuel is exhausted, the outward forces of radiation diminish, allowing the gravitation to compress the star inward. The contraction of the core causes its temperature to rise and allows remaining nuclear material to be used as fuel. The star is saved from further collapse -- but only for a while.\n\nEventually, all possible nuclear fuel is used up and the core collapses. How far it collapses, into what kind of object, and at what rate, is determined by the star's final mass and the remaining outward pressure that the burnt-up nuclear residue (largely iron) can muster. If the star is sufficiently massive or compressible, it may collapse to a black hole. If it is less massive or made of stiffer material, its fate is different: it may become a white dwarf or a neutron star\n\nThe gravitationsl pull of black hole is so powerful that it can even suck in light.\n\nThere is a theory that what gets suck by black holes is thrown out by a "whitehole" that matter travels through a "wormhole". But if this is true then may be one day we may travel with or more than the speed of light to reach very very far away points in the universe.\n\nFor more information search http://www.google.com for black hole.
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A black hole will only form for stars that have a mass greater than or equal to approximately 25x the mass of our sun.\n\nLet me back up a little.\n\nStars are basically a huge ball of gas that is burning at astronomically high temperatures.  The only thing holding this giant bomb together is its own gravity: it is so massive that it holds itself together.\n\nEventually, though, enough of the star has burned up so that its mass drops enough so that the explosive force of the nuclear reactions push it outward - this is a supernova.\n\nWhen stars are 25x more massive than our sun (or more), there is so much mass that all the mass collapses back in on itself, forming a black hole.\n\nA dying star will never collapse back into a black hole; that is the essential difference.
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A Star's Size:\n\nA star begins its "life" in a contracting nebula of gas and dust. As the density of the material increases under the influence of gravity, compression heats the material. If the material gets hot enough, hydrogen atoms begin fusing together to form helium atoms, and a star is born. A star will spend most of its life, called the main sequence phase, fusing hydrogen into helium.\n\n  \nIt's logical that a large nebula (one with a large amount of mass) will form a large star, and a small nebula will form a small star. However, in addition to a star's initial mass, a star's size also depends on the balance between the inward pull of gravity and the outward push of the energy produced by fusion. The entire sequence of a star's evolution can be described in terms of the changing balance between these two opposing forces.
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To Answer the First part:\n\nThe life of a star is a continual struggle between the two forces of GRAVITY and NUCLEAR ENERGY. \n       The star’s self gravity or weight tries to compress the star into a smaller sphere of gas. But when a gas is compressed it gets hot, and in the core of a star the gas gets so hot (10 million Kelvins or more) that nuclear reactions occur. In a star like the Sun the nuclear reactions release more energy each second than one billion hydrogen bombs. As this energy works its way out of the star it balances the star’s self-gravity. For most of a star’s life an equilibrium is maintained between self gravity and energy.\n\nPSS Part 2\n\nNot sure what they want here.  Since the "young star" is formed from the older star dust, it would have a higher proportion of heavier elements (like Iron and Silicon), since those elements would have been created in the older stars.  A new protostar would never have been exposed to these heavier elements, so it would be still Hydrogen and Helium.
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I am not quite sure what your asking.\n\nWhen the star is forming, it starts out as a gigantic cloud of mostly Hydrogen. As the stellar material coalesces, the material begins to heat up and the pressure at the center of what will become the new star increases dramatically.  The material becomes denser and is pulled together by its own gravity, heating up as the pressure rises.  Gravity is working to pull the star together, and eventually the ball of gas becomes so massive, that the pressure and heat at its core are sufficient to undergo nuclear fusion.  In order to counteract the force of gravity, the Hydrogen at the stars core undergoes fusion, in the process, producing Helium and a lot of energy.  It is this energy produced from nuclear fusion at the stars core that keeps the star from collapsing in on itself.
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Probably just as big as it is now. Its diameter is 864,938 miles (109 times the size of Earth). \n\nThe sun is over 4.5 billion years old... so a billion years ago it was doing pretty much the same thing it is now. A lot of nuclear fusion going on. \n\nIt will stay the same size until it has used up its core hydrogen fuel, the star starts to fuse helium and eventually other elements. During this time the star will expand into a red giant or super-giant, becoming tens or even hundreds of times larger. Eventually, no more fuel will be available and the star will collapse under gravity to form a white dwarf star only a few thousand kilometres in diameter.
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Correction: when stars "die", they either become a white dwarf (if they're light, where all elements are reduced to primarily iron, which has a lower energy state than anything lighter or heavier--hence, it becomes spent nuclear fuel that cannot react anymore), or a neutron star (as above, but with a mass so great that gravitational forces overwhelm nuclear forces making electron collapse into protons in a single mass), or they can become black holes (if their mass is so very great that all matter is compressed into a singlarity--ie, a point with infite density).  The mass of a black hole is guaged by the degree to which it curves the surrounding space-time continuum.\n\nA white dwarf glows as it is white-hot, but as it cools down, it becomes a brown dwarf, turning dark.\n\nThe debate in astronomy is whether the rate of the universe's expansion is sufficient to keep all black holes from collapsing.  On either end, a break prediction lies: in one scenario, everything forms one big singularity, while in the other, energy fluctations slowly even out until entropy is optimized throughout the universe, resulting in the "heat death" of the universe.
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Our sun will never go supernova or form a black hole. It doesn't have enough mass for that. It will, however, become a red giant and eventually cool down as others here have pointed out.
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Actually the sun does not have enough mass to go supernova, after becoming a red giant its radius could actually get as big as earth's orbit, and once this happens it will lose its layers in what is called a "planetary nebula" which believe it or not has nothing to do with planets, and after this it will become a white dwarf and eventually burn out.
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throughout a stars life-cycle, it is constantly heating materials (hydrogen and iron) and pushing them to the surface to cool, and to the center to heat up and melt.\nThis is part of nuclear fission.\n\nafter a very long time, the sun starts to lose energy, and cant push the iron up from its core and gradually grows larger, turning red (hence red giant),\nEventually, the pressure from its mass, and it's failure to push it all away from its core will result in the star collapsing into itself, potentially turning into a black hole.
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A star by the burning of hydrogen into helium can only go so far into making the heavier elements. It takes a supernova explosion to make the really heavy elements. These are blown out into space where new stars may form and use these heavier elements, like our sun and earth.