Type1Supernova result from white dwarf stars that have reached a mass of__suns from material transferred?
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.
728755
The Sun's current age, determined using computer models of stellar evolution and nucleocosmochronology, is thought to be about 4.57 billion years.[4]\n\nThe Sun is about halfway through its main-sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than 4 million tonnes of matter are converted into energy within the Sun's core, producing neutrinos and solar radiation. The Sun will spend a total of approximately 10 billion years as a main sequence star.\n\nThe Sun does not have enough mass to explode as a supernova. Instead, in 4-5 billion years, it will enter a red giant phase, its outer layers expanding as the hydrogen fuel in the core is consumed and the core contracts and heats up. Helium fusion will begin when the core temperature reaches about 3×108 K. While it is likely that the expansion of the outer layers of the Sun will reach the current position of Earth's orbit, recent research suggests that mass lost from the Sun earlier in its red giant phase will cause the Earth's orbit to move further out, preventing it from being engulfed. However, Earth's water and most of the atmosphere will be boiled away.\n\nFollowing the red giant phase, intense thermal pulsations will cause the Sun to throw off its outer layers, forming a planetary nebula. The only object that remains after the outer layers are ejected is the extremely hot stellar core, which will slowly cool and fade as a white dwarf over many billions of years. This stellar evolution scenario is typical of low- to medium-mass stars.[5][6]
1009893
It is possible that the class of giant gas planets might merge into brown dwarfs at the upper end of the scale. However, a brown dwarf, while it does not have enough internal pressure to fuse hydrogen into helium, can fuse deuterium.  There's not much deuterium, so they don't burn very brightly or for very long, but this brief burst of fusion power makes them stars of a sort. \n\nBrown dwarfs range in size from about .013 solar mass (~13x the mass of Jupiter) to .08 solar mass.  Smaller bodies might be planets, slightly larger bodies are red dwarf stars.
961557
The stars emit particles that reach us.
97241
Supernovae throw off some heavy crap when a star explodes.\n\nTake a look at the following link.  The graphe shows that iron is a special element.  When you fuse lighter elements, you release energy, and when you let heavier elements decay, you get energy.  But iron is going nowhere.  So a star starts out with lighter elements, which fuse and create heavier elements.  The more the sun uses up the small elements, the denser the core gets, and the more rapidly it fuses in the core.  Eventually, when most of the elements are used up, you'll have the core collapse and throw off the outer layers in a massive thermonuclear explosion.  The remaining material will mostly be iron, and the star will glow white-hot as a white dwarf for many years, until it evenbtually cools off and goes dark.  But some heavier elements will be thrown off by the explosion, including some that, in the rapid collapse, jumped the iron gap and absorbed energy from the nuclear explosion to become heavier than iron.  These heavier things will decay over time, releasing energy by fusion.
652025
Many stars are between 1 billion and 10 billion years old. Some stars may even be close to 13.7 billion years old, which is the observed age of the universe. (See Big Bang theory and stellar evolution.) They range in size from the tiny neutron stars (which are actually dead stars) no bigger than a city, to supergiants like the North Star (Polaris) and Betelgeuse, in the Orion constellation, which have a diameter about 1,000 times larger than the Sun—about 1.6 billion kilometers. However, these have a much lower density than the Sun.\n\nOne of the most massive stars known is Eta Carinae, with 100–150 times as much mass as the Sun. Recent work by Donald Figer, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, suggests that 150 solar masses is the upper limit of stars in the current era of the universe. He used the Hubble Space Telescope to observe about a thousand stars in the Arches cluster, a massive young star cluster near the core of the Milky Way, and found no stars over that limit despite a statistical expectation that there should be several. The reason for this limit is not precisely known, but the Eddington limit is part of the answer. The very first stars to form after the Big Bang may have been larger, up to 300 solar masses or more, due to the complete absence of elements heavier than lithium in their composition. This generation of supermassive stars is long extinct, however, and currently only theoretical.\n\nWith a mass only 93 times that of Jupiter, AB Doradus C, a companion to AB Doradus A, is the smallest known star undergoing nuclear fusion in its core. Smaller bodies are brown dwarfs, which occupy a poorly-defined grey area between stars and gas giants. The minimum mass a star can have is estimated to be in the vicinity of 75 Jupiters.
887560
while these answers are correct on the minimum mass necessary to sustain hydrogen fusion (Look up "L" stars), they miss the boat on why stars cannot be more massive than a certain amount.  \n\nAs you may know, as you look at more and more massive they become brighter much faster than you might expect (for instance a star ten times as massive as the sun may be about 3000 times brighter!).  They get a little bigger, but mostly they become more luminous per area.  At some point they are so luminous that atoms on the surface are lifted off in a stellar wind quite rapidly.  Extremely massive stars evaporate quite quickly, reducing their mass and thus their luminosity until they are not evaporating so quickly.\n\nWiki has an OK treatment of this concept which was originally applied to the problem of how quickly an object can accrete material. \nhttp://en.wikipedia.org/wiki/Eddington_limit\n\nThe actual luminosity limit is lower, because the effective cross section of the gas to photon interactions is dependent on opacity. For pure hydrogen the electron scattering cross section is the one to use, but as soon as you put in a few heavy elements (heavier than helium) it goes up very quickly for even small concentrations. So far, amongst non-primordial stars, the most massive ones we seem to see are around 100 times the mass of the sun.  60 is the lowest upper limit I have ever heard and 120 is about the highest.\n\nEarly first generation stars made from pure primordial hydrogen, helium and a dash of lithium would very likely only be limited by the opacity used in the Eddington limit. I estimate these guys would top out around 200 solar masses.
524772
This happened in three ways.\n1) at the time of the Big Bang the matter was very dense. Because of this about a quarter of the available protons got changed into neutrons. These fused with protons to make principally Helium, heavy hydrogen and a tiny bit of Lithium.\n2) this mixture ended up in the first generation of stars.\nDuring their lifetime hydrogen was again fused mainly into helium, but also heavier stuff, like oxygen, sulfur and a few more elements upto iron\n3) the bigger stars of the first and later generation explode at the end of their life, when there is no longer enough fusion going on in their cores for lack of elements to fuse. The supernova explosions produce a lot of neutrinos. Neutrinos are capable to transmutate elements into others. In this proces all the elements are produced even the ones heavier than iron.\n\nHow do we know this?\n\nThese three processes can be modeled and calculated on computers. These models give predictions on the amount of helium and other elements produced in the Big Bang and in supernovae. These predictions can be checked against the actual abondance of the elements in stars, in the solar system and in the earth's crust.
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Stars gain their energy through gravitational collapse. \n\nWhen the collapse raises core temperatures and pressures sufficiently, nuclear reactions begin. These reactions produce a lot of energy and a lot of photons. The photon pressure is sufficient to stop further collapse of the star.\n\nWhen the fusion materials are exhausted, collapse resumes. The core temperature and pressure then rise. When they are hot enough, further fusion of larger atoms occurs.\n\nThis continues up the periodic table until fusion is no longer possible. \n\nThe star then coninues to collapse to a very hot, degenerate ball. In some cases the temperature on the surface then gets high enough to cause a catastropic runaway fusion reaction of the helium on the surface, because the rate of fusion of helium is temperature dependent. \n\nThe start the explodes as a supernova. This throws off some matter (though not actually that much). The very high energy of the explosion is enough to produce heavier elements through nucleosynthesis.\n\nWhat is left is a tiny but very very hot star called a white dwarf. Because it is so tiny, it does not radiate much energy (it has a small surface area) so it is quite dim.
817154
Sirius B is one of the most massive white dwarf known.  Its volume is about the same as Earth, but the mass is comparable to that of the Sun. Since the mass of the Sun is approximately 333000 times that of the Earth, and that Earth has a density of 5.5, we have a specific density of 1800000 for Sirius B. That means 1 cubic cm of Sirius B should have a mass of 1800000 g,\nor 1800 kg, or 1.8 tonne (about 2 tons). So, this is not quite the 50 tons you were told.\nThat said, one may have been talking about the *core* of the star, where density is evidently a lot higher than the average for the whole star.
321257
We do this all the time today.  We have many times looked into the heart of a planetary nebula (leftover from the death of a low mass star) or a supernova remnant (leftover from the death of a high mass star) to see the small compact objects left over after the star has died.\n\nIn the case of a low mass stars we see many white dwarf stars, and for the high mass case we see neutron stars.  A good example is the pulsar we have seen in the Crab nebula, or the white dwarf at the heart of the Ring nebula.
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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!)
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Birth and death of stars is an interesting subject, IMO.\n\nHere are some starting points:\n\nhttp://en.wikipedia.org/wiki/Star\nhttp://en.wikipedia.org/wiki/Hertzsprung-Russell_diagram\nhttp://en.wikipedia.org/wiki/Supernova\nhttp://aspire.cosmic-ray.org/labs/star_life/starlife_main.html\nhttp://www.windows.ucar.edu/sun/Solar_interior/Nuclear_Reactions/Fusion/Fusion_in_stars/star_life.html
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Most probably, none, for brown dwarf stars are sub-stellar objects with a mass below that necessary to maintain hydrogen-burning nuclear fusion reactions in their core.  Without hydrogen one of the primary building blocks for the inception of life, an Earth like planet, or even a remotely similar planet, having polybiological opportunities for the generation of life could not be formed.  The only planet known to orbit a brown dwarf star is 2M1207b.  Furthermore, there is speculation that even the presence of hydrogen is not enough to create the conditions ripe for the emergence of life, for quantum equations completed 6 years ago reveal that our G-2 class star is far too small to have created the heavier rare elements in the human body and on Earth.  These elements can only be generated by a Blue Supergiant.  Hence, our Sun is not our paternal star, and Earth-like planets are the by-product of Blue Supergiants, not G-2 class stars.
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
727897
Supernovas.  Blackholes don't give much back to the universe other than minute sub atomic partices (and not even many of those); similarly with neutron stars.  The sun makes heavier elements like iron, but not the heaviest.
276357
A (type II) supernova is the natural end of a massive star atleast 8 times more massive than the sun. The energy for the explosion is generated by a catastrophic gravitational crunch (as opposed to a type I supernova which is an actual nuclear detonation. They are probably caused by two white dwarfs colliding.)\n\nAs a massive star runs out of hydrogen in its core it  contracts and gets hotter until heliumfusion begins. When an average mass star, like the sun, enters this stage it is the end. The core doesn´t have enough mass to fuse elements heavier than helium and a white dwarf remains.\n\nIn heavier stars the fusion processes goes through increasingly heavier elements with the core getting smaller and hotter in each step. When silicone has fused into iron the end has come. Iron is too tighly bound in its nucleus to allow more fusion despite a temperature of 3 billion degrees. With no more energy keeping the core up it collapses with a quarter the speed of light. It shrinks from the size of earth to a sphere only 100 km in diameter in less than one tenth of a second. The gravitational energy released in that instant is 100 times greater than all the energy the sun has put out in all its 4.6 billion year lifetime. Needless to say the star explodes. A super nova is born.\n\nThe core remain however and it contracts so much that, when the core is only 8 km in diameter, protons and electrons cannot exist anymore and you have a neutron star.\n\nIf the mass of the core is greater then 3 solar masses then not even the neutrons can keep the neutron star from contracting further. In stead it shrinks and shrinks and shrinks until the density of the object is infinite. It is now a singularity. We call such singularities black holes because we can´t actually see them. The escape velocity is greater than the speed of light and since nothing can travel faster than light they are truly black. We can only see the effect the gravity of a black hole has on nearby stars.