How is a star formed?
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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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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.
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A black hole is formed by a star, most likely a neutron star, collapsing into a space a few kilometers across. It is made up of the same thing a neutron star is, mainly hydrogen, helium, oxygen, and a few other elements. Once the black hole forms, it can absorb large amounts of matter from surrounding stars.
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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. \nThe 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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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.
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Planet formation is still somewhat of a mystery, but astronomers believe they understand the basic process. The best explanation to be accepted by most astronomers is known as the solar nebula hypothesis. Stars are formed from giant clouds of gas and dust known as nebulae. Gravity causes the matter in the nebula to coalesce. Gravity soon causes the central part of the nebula to collapse and form a star. The rest of the gas and dust forms a flat, rotating ring around the new star. Eventually the gravity of the new star begins to pull matter towards it. Small whirlpools of spinning matter form within this disk. Gravity causes these whirlpools to aggregate into small masses known as planetesimals. These planetesimals continue growing, pulling in the matter around them. Gravity soon pulls them into a spherical shape. These small spheres may collide and merge with others as they grow in size and become what is known as a protoplanet. Sometimes, a smaller sphere of matter may become captured by a larger one and enter into an orbit, creating a moon. Over time, gravity causes the heavier elements in the protoplanets to separate from the lighter ones in a process called uniformitarianism. This forms the planet's metal core, rocky crust, and usually an atmosphere composed of gas. As the star and planets continue to grow, the dust and gas of the nebula begins to thin. Smaller chunks of condensed matter is left over in the outer regions of the disk. These form the Kuiper belt of planetoids and the Oort cloud of comets. Eventually the solar wind from the star will blow away the excess gas and dust. A new solar system has been born. The process is slow and takes millions of years. Many stars have been observed to have flat disks of matter around them. These could very well be new solar systems in the making.
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In lay man's terms:\n\nA star: a huge ball of fire, emitting heat and light, mostly composed of gasses and the source of the heat is the nuclear reactions happening isnide it due to the massive pressure in its core. An example is the sun, the temperture of its surface if more than 5000 degress centigrade, while the temperature of its core is several million degrees. A star is 'usualy' much larger than planets(thouthands to millions of times larger) . Some stars have planets orbiting around them (e,g, our sun)\n\nPlanets: Intert masses that do not emit light or radiate heat. Planets revolve around stars and are far much smaller than stars(e.g. earth, mars, saturn, jupiter,etc). Some planets have moons(much smaller planets) revolving around them.Mostly planets are solid masses, but sometimes they are made of gases. The temperature of planets is far cooler than stars.
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A star forms in a nebula which is a very large cloud of hydrogen gas.  hydrogen is the basic building block of the universe.  A prostar is formed when a portion of the hydrogen in the nebula is formed into a hydrogen ball by the pull of gravity.  When the molecules become close enough the friction of their bumping together causes heat.  If it were not for this heat production the prostar would be pulled into a clump by the force of gravity.  Once enough heat is formed in the core of the prostar (about 2 million degrees) hydrogen nuclei join together to form a helium molecule.  The reaction is 6 H >1 He + 2H  That means 6 hydrogens are needed for the process to proceed, but two hydrogen are reclaimed on the other side so the net rxn is 4h > 1 He.  This reaction is possible because of entropy or the conservation of energy.  It takes less energy to maintain one atom of Helium than 4 atoms of hydrogen.  In the sun this energy savings is 0.6% which radiates to the surface and is expelled as sunlight.  Within the Sun about 745,000 tons of Hydrogen is converted to Helium every second.  The balance of the pull of gravity (collapse) and the heat from nuclear fusion (expansion) keeps the star's size and shape constant.  Once this process begins the prostar becomes a star.  There are other nuclear fusion reactions untill the formation of iron.  This step does not give off energy but requires energy input.  At this step stars begin to cool and become a red giant.  This is the first step in the death of a star, resulting in the formation of a nova or a supernova depending upon the size of the star.  a smaller star will form a white dwarf and the larger star will form a neutron star or if large enough it may collapse into a black hole.  Gravity is the attraction of particle to particle between two objects.  This is how a black hole works.  It has an extreemly strong gravitational pull because the core is composed of a very large amount of compacted particles and each of those particles contribute to the gravitational attraction.
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Stars use nuclear fusion to liberate the energy we perceive as light and heat.  When a star runs out of Hydrogen to fuse, it begins to fuse Helium.  This continues up the chain of elements up until Iron.  A star cannot make the jump in energy needed to go beyond this point.  With each change in fusion matter, the stars energy output increases, more heat causes the star to expand more and more.  If the star is massive enough, when it "runs out" of fuel, it will collapse upon itself in one final massive explosion of energy.  We call these Nova, or Super Nova.  The remnants of smaller Nova are Pulsars, or Neutron Stars.  The only matter left are Neutrons, no protons or electrons, no electron cloud.  Tightly packed, the material from a Neutron star is the most dense substance known.  If the star is too massive to form a Neutron star, it forms a Black Hole instead.  Stars that are not massive enough to go Nova, just burn out and cool to a brown dwarf.
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To simply, the sun is basically a gigantic collection of hydrogen gas that is being pushed together by an enormous force of gravity (each particle of hydrogen gas attracts each other).  When those atoms are forced together, they interact to form a continuious nuclear reaction which effectivly acts as a counter-force to the force of gravity.  So: Gravity pushes in, a nuclear explosion pushes out and the particles come to an equilibrium giving the sun a particular size.\n\nAs a star grows older, it begins to exhaust its supply of hydrogen fuel for the nuclear reaction and increases in size while decreasing in temperature.  At some point in the lifecycle of our sun, its size will actually expand to include the current position of the Earth.  However, current models indicate that Earth will move farther out in orbit, preventing its engulfment and destruction.\n\nAt any rate, as _our_ star (the Sun, sometimes called "Sol") continues to grow older, it will eventually shed these outer layers (thus creating a nebula) and condense into a very dense core and over time radiate away its energy.\n\nVery large stars can form black holes or neutron stars, regions of extreme gravitational forces, but our sun is small enough that it will form neither of these and just cool down into an inert ball of chemicals, no longer shining after it has radiated away its energy.\n\nHope that is helpful.
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The elements are formed in the Universe in three different places and times.\n\n1) In the three first minutes after the Big Bang protons and neutrons were formed. Roughly a quarter of those combined into helium, deuterons (heavy hydrogen) and a tiny bit of lithium.\n\n2) Stars like the sun are made of 75% hydrogen, 24% helium and 1% of other stuff. Their cores are hot enough to fuse hydrogen into helium. When the hydrogen in the core is exhausted the star goes through the red giant state in which it fuses helium into heavier elements like oxygen, sulphur all the way up the periodic system upto iron.\nThe smaller stars blow their outer layers into space.\n\n3) The bigger stars however, say 5-8 times the mass of the sun explode. These are supernovas. During this explosion a large part of the energy is liberated in the form of neutrinos.\nAn incredible amount of neutrinos, in fact. These particle are capable of transforming elements into others as they can change neutrons into protons. These reactions produce the elements heavier than iron.\n\nHow do we know this? \n\nAll three processes have been modelled. These models predict abondances for the elements in the universe. Those can be mesured are turn out quite close to the predictions.
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A star is any massive gaseous body in outer space, just like the Sun. Unlike a planet, a star generates energy through nuclear fusion and therefore emits light. All stars except the Sun appear as shining points in the nighttime sky that twinkle because of the effect of the Earth's atmosphere and their distance from us. The Sun is also a star, but it is close enough to Earth to appear as a disk instead, and to provide daylight.
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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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I assume you mean a black hole. Only some stars produce black holes. A star has to be big enough and meet some other conditions so that when it's life is over, and it starts to contract into a compact mass, that the gravity is enough to create a black hole.\n\nThe inward falling surface goes so fast that it approaches the speed of light. This is at the Schwarzschild radius, and it is sort of the edge of the black hole, also called the event horizon. \n\nA black hole is just a region of space where our known laws of physics do not apply. There is of course much more to this story, but this might get you started.
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Our sun began forming within an immense interstellar cloud of drifting gas and dust. Inside this cloud (called a 'nebula') were regions of relatively high density where gravity began drawing together bits and pieces of the gas and dust. Over several million years, this spherical region became denser and denser which caused its central temperature to rise. Finally, some 4.5-billion years ago, the temperature was hot enough to start nuclear fusion. Our sun was born.\n\nGod should be spelled B-I-G B-A-N-G\nPBrax@netscape.com
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First, our sun has a long time to go before it could possibly become a supernova, not for billions and billions of years, so don't worry about it, if you were worrying. OK?\n\nNow, the way a star burns is by fusion, which is building up heavier elements by fusing atoms of lighter elements together. The typical start starts out as hydrogen, and it fuses the hydrogens together into helium. \n\nWhat happens when a star runs out of hydrogen? It starts fusing the heliums together into heavier elements. In order to begin this process, the star has to contract, to squeeze everything together to make the core temperature hotter. \n\nNotice that when the star began to run out of hydrogen, it cooled off a little. So the temperature of the star fluctuates. Its size fluctuates too, since the heat energy partly counteracts the gravity that holds it together.\n\nSo, the star cools off a little, it contracts, and we call this a pulsating or variable star. (This is somewhat of an oversimplification; there are different types of variable stars. But I am ignoring them for purposes of this illustration.) Then the star begins fusing helium, and heats up again. The star expands. \n\nThe outer surface of the star explodes away in what we call a nova-- not a supernova, yet. Some of the gas rushes away and may form what is called a nebula, a cloud. some of thee nebulas give off pretty colors, because, just like a neon sign, the gas in them is excited by the energy of the star and glows.\n\nSo, after repeated cycles of this, and bazillions of years, the star is exhausted. When the star gets iron in its core, there is no turning back. You can't fuse iron into anything. \n\nBut, you say, what about those elements that are heavier than iron, like gold and mercury and uranium? Ah, I'm so glad you asked about that. That is where the supernova comes in. \n\nA supernova is the death of a star. A nova flares up and puts out lots of energy, but the supernova puts out as much energy as the star might have put out over its entire lifetime! The last time there was a supernova in our galaxy (the Crab Nebula was formed) in 1054 AD. The Chinese were the only ones whe were doing much astronomical observation then. \n\nBut it was visible in broad daylight! From LIGHT YEARS away!\n\nWhat happens is this: the star begins to contract one final time. Most of the star blows away, making a really, really impressive nebula. All the elements that were built up in the final explosion-- all the heavy elements beyond iron-- get flung out into space, where they might meet with other elements and form planets and things.\n\nWhat happens to the rest of the star? One of three things, depending on how big it is. If it is little, it may form a white dwarf, a little star that is not so big but is now mostly hydrogen and helium and will last a long time. I think they are supposed to expand into red giants when they are about to burn out, but I don't remember for sure. \n\nIf the star is medium sized, it may become a neutron star. It is no longer buring with fusion like a regular star. The nuclear particles in its core are squeezed together so that protons and electrons have lost their identities and everything is neutrons. This is as solid and dense as matter can get, neutronium. It has an incredibly strong magnetic field, bazillions of times anything on earth.\n\nThe star's axis of rotation may not line up with the magnetic poles (just the way Earth's magnetic poles are not right at the true north and true south poles.) If this hapens, and the magnetic poles are pointed in the right direction, then every time it points our way, we see a little 'flash' of magnetic energy, and we call these 'pulsars'. The first time anybody detected them, they thought they were radio signals from people in space, because they were so regularly-spaced. It is a good thing there are no pulsars near Earth, because the flashes of intense magnetic fields would fry us lik
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Planetary nebula are formed after a supernova explosion.\n The remains of a giant star that has consumed its fuel.