How long does it take for a star to explode?
550492
The collaspe of the core is over in seconds but it takes hours for the outer layers to actually get blown off (and thus it is hours from when the neutrinos get emitted and when we actually see any light from the thing).
456739
They need to reach what is known as the 'Chandrasekhar limit'.  This occurs at 1.4 solar masses.  It's at this point that the gravity overcomes the support of the white dwarf, and it collapses, then explodes.
294760
Mostly hydrogen gas, I suppose with some other elements and dust. As the star ignites, the gasses are blown further out, with the heaviest atoms and molecules remaining in-system.
49829
check this site...\nhttp://www.bbc.co.uk/science/space/stars/index.shtml
65546
A supernova is the death of a supermassive star.  Our sun converts Hydrogen into Helium right now.  When all or most of the Hydrogen has been converted, the Sun will heat up and start fusing Helium atoms together.  The Sun will continue to fuse heavier and heavier elements until it gets to Iron.  The increase in energy needed here is too great.  Our sun is average, it won't Supernova.  Much more massive stars when they reach this point collapse in on itself because there is no nuclear furnace keeping gravity in check.  The resulting explosion releases massive amounts of energy, creates elements heavier than Iron, and leave either a nuetron star or a black hole where the original star used to be
62632
Depends on the mass of the star....but for example for a star with mass similar to the Sun..\n\n1. Protostar contraction for roughly million years or slightly less.\n2. Main-sequence for roughly 9 billion years.  In this stage the core is burning hydrogen to helium.\n3. Giant stage.  Where the core that is filled with helium compresses and starts to heat up and make star expand.\n4. Planetary nebula\n5. White dwarf\n\nSome massive stars will burn other elements like helium and carbon and can turn into neutron stars or black hole.  Black holes happen for stars greater than roughly 25 solar masses.
732762
Their materials collect together (via gravity) and make new stars.  Granted, they tend to be made of heavier materials and burn cooler (often red).\n\nStars collapse when they run out of material.  A star begins by fusing hydrogen into helium.  Eventually, the hydrogen runs out and the star begins to collapse until it is able to fuse helium into carbon.  This continues through various elements until it is largely iron.  A star is simply not able to fuse iron into anything else (their not massive enough), so it eventually has a final collapse, sometimes into a supernova.\n\nThis final collapse can leave three possible "leftovers":\n1.  A white dwarf - if the star is less than 3 x the mass of our sun, then the core will be left as a burning ember.  Eventually it will burn out to become something known as a brown dwarf, a dead star.\n\n2.  A neutron star - if the star is between 3 and 10 (I think) x the mass of our sun, the explosion compresses the core down enough that protons and electrons are crammed together to form a neutron star.  It's a bunch of neutrons so dense a teaspoonful would weigh, well, tons on the earth.\n\n3.  A black hole - if the star is especially massive, the collapse never ends.  The core itself cannot overcome the massive gravity that is created by a now extremely dense remnant, forming a black hole.
696504
A supernova (pl. supernovae) is a stellar explosion which produces an extremely bright object made of plasma that declines to invisibility over weeks or months. A supernova briefly outshines its entire host galaxy. It would take 10 billion years for the Sun to produce the energy output of an ordinary Type II supernova.[1]. The Sun is notably too small to ever become a supernova—rather it will become a White Dwarf (see Chandrasekhar limit).\n\nThere are several different types of supernovae and two possible routes to their formation. A massive star may cease to generate fusion energy from fusing the nuclei of atoms in its core, and collapse under the force of its own gravity to form a neutron star or black hole. Alternatively, a white dwarf star may accumulate material from a companion star until it nears its Chandrasekhar limit and undergoes runaway nuclear fusion in its interior, completely disrupting it. This second type of supernova is distinct from a surface thermonuclear explosion on a white dwarf, which is called a nova. In either type of supernova, the resulting explosion expels much or all of the stellar material with great force.[2]\n\nThe explosion drives a blast wave into the surrounding space, forming a supernova remnant. One example of this process is the remnant of SN 1604, shown to the right.\n\n"Nova" is Latin for "new", referring to what appears to be a very bright new star shining in the celestial sphere; the prefix "super" distinguishes this from an ordinary nova, which also involves a star increasing in brightness, though to a lesser extent and through a different mechanism.
310303
Usually what happens is a large event such as a supernova will destroy an old star, kicking out elements. Here's how it's believed to have happened before this solar system was formed, since it's believed that the sun is only a 500 million years older than the planets:\n\nWhen a star is about to die, its last stages of life consume a lot of different materials (this is assuming this star is large enough to create a supernova).  When it runs out of hydrogen, it begins to fuse helium, when that runs out, it goes to lithium, then on down the periodic table, until iron, which requires too much energy to fuse, and the fusion within the star ceases.  What happens here is tight . . . lets establish this first:\n\nStars are composed of mostly hydrogen and helium, little bit of lithium, and much much less of the heavier elements . . .  \n\nWhen the iron is left to fuse and it can't be done, the internal pressure from the core, which is generated by fusion, is lost, and the top shell of the sun is left to be supported but, since the fusion pressure has ceased, there's nothing to keep it up, and the outer shell of the star collapses.  This massive collapse of all that material to the leftover core compresses the inward falling material, increasing pressure and when that material hits the inner core, it 'bounces' back out violently, releasing massive amounts of energy, shooting the entire outer portion of the star into space. This is the moment in which heavy elements are made, in supernova events. The universe at one point did not have much by way of heavy elements, but as more and more stars collapse and supernova, they create more and more heavier elements; the origin of the diversity of the periodic table is here.\n\nFrom this you could assume, that as the universe gets older, stars are going to be creating and spitting out more and more heavy elements, and since stars cannot really use heavier elements to fuse, the number of stars over billions of years will slowly start to decline.
579859
I assume you mean "star" and not "sun", as in OUR sun, in the first question.  In that case, a supernova is essentially the spectacular explosion that occurs when a star of a significant sized mass ends its life.  IN that case, all the elements with a periodic table number higher than oxygen are created.  In addition, the remaining core of the dead star becomes so dense, that it creates an object that even light can't escape.  This object is now a black hole.\n\nOur sun is not big enough to supernova, therefore it will just die out and become a black dwarf when it is dead.\n\nDefinition from the Big Wiki...\n\nhttp://en.wikipedia.org/wiki/Supernova
312576
Stars are big fiery balls of gas. Essentially the gases cluster together and become stars through gravity and fusion. It's a rather complicated process; check the link below for a more detailed explanation.\n\nStars appear to be in our sky because they are in space. Most stars appear to be small points of light, although many of these stars are smaller than our sun. The sun simply appears larger because it is much nearer to the Earth.
577912
About ten minutes after the sun goes supernova
1138397
A star produces atoms in nuclear atomic chemical fusion or fission reactions.\nThe lifetime of a star takes fusion:\n3x4He > 12 C\n4 He + 12 C > 16 O plus 2x12 C > 20 Ne + 4 He\n56 Fe = Iron\n(4 He + 12 C = 16 O)+(2x12 C = 20 Ne + 4 He)_20 Ne + 4 He + 2x16 O\n= 56 Fe\nAs Iron consists to the sun's sunspots now for a magnetic field or liquid Iron of 5,000*C this gives the impression it is black against an even more hot and brighter gassy nuclear background.\nBut when the sun begins too end it's life the fusion reaches oxygen and then reaches Iron (Fe) and Beryllium (Be).\nAs the sun is completely filled with Be and Fe at the core. As metal absorbs energy and nuclear and gas forces out then the absorb from the metal core and as energy is released from the outer layers the star is unstable and is formed as a variable. The outer layers are swapped with the inners and the new outer layers are pushed off and out to a red giant until the core revs and the red giant keeps size for a while until a new process begins and the new inner layers of Oxygen from the old outer layers and the Oxygen keeps the red giant pushed out to size and then the whole star is cast as gas/plasma Iron and the star's power, heat and energy accelerates the star and with Oxygen inside, the explosion is created and a new atom is created, Gold.\nThe minerals create stars from 116 elementary chemicals.\nThe stars are made in the nebulae and new stars are made and so are planets. Thus the planets and stars create life from their chemicals and their chemicals come from the supernova.
327270
When a star runs out of fuel, it explodes its outer layer off in a Nova, while the core collapses inwards. Because the continual fusion reaction has stopped, there's nothing to stop the collapse until all of the residual matter presses against each other. This is called a Brown Dwarf.\nIf the star is much larger than our Sun, gravity is so strong that even the matter collapses until the atoms' neucleii press against each other. This is called a Neutron Star.\nIf the star is still larger, not even the neutrons stop the collapse, and gravity causes the whole lot to collapse to a pinpoint. The gravity is still there, sucking in everything around it, even light. This is called a Black Hole.
534669
After a star dies, there is still some residual heat left over. That heat makes the star (white dwarf or neutron star) glow, even though it is not producing any energy. Eventually, the star cools off and does indeed simply become a hunk of ash, which we call a "black dwarf." \n\npeace
1185197
Our sun will not explode. It will eventually burn out in about est. 5 billion years. Then, for the next several million years it will swell to a red giant which will possibly engulf the Earth and quite possibly Mars. Then eventually the remainder will be pushed off into space and it will shrink to a white dwarf.
878404
As a matter of fact, nuclear explosions occur in space all the time, the sun and billions of other stars in the universe are fuelled by the nuclear fusion of hydrogen atoms into helium as we speak. The light  we see from the sun and stars are a result of this nuclear fusion. So  the energy from a man made nuclear bomb would be neglitable