how are stars formed?
819359
Stars begin as large spheres of hydrogen gas. Due to compression of this gas under the force of gravity, the center of the sphere can get as hot as 10-million degrees Kelvin. At that temperature, nuclear fusion (..the same process that happens in a hydrogen bomb) can begin and a new star is born.
300263
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
188339
Yes. Starting from hydrogen, every element is produced inside stars by nuclear fusion. It's a cascade process: light elements join to form heavier elements, all the way down from hydrogen.
654297
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.
313861
YES. There are many stars in our galaxy with solar system formed.
1104100
The protons and electrons formed into stellar bodies. The stellar bodies converted the hydrogen into helium, carbon, nitrogen, and some other lighter elements.   \n\nStars with a mass of more than 5 solar masses are subject to becoming supernova--a massive stellar explosion.  The energy produced by that explosion produced all of the heavier elements and distributed them throughout the galaxy where they were captured by other gravitational fields.
1113863
The star begins as a cool cloud of gas, well to the right Under its own gravity, the cloud begins to collapse. As it collapses, it releases its gravitational energy as radiation. So a young star is cool but bright. We usually don't see these proto-stars, however, because they are generally shrouded in dust and only give off light in the far infrared part of the spectrum. \n\nThe proto-star continues to collapse, and as it does, it gets hotter and hotter. "Stars" less than a percent of the Sun's mass eventually halt their collapse due to gas pressure. These stars are "brown dwarfs" or "giant planets," like Jupiter. They never ignite their hydrogen, and gradually dim away.\n\nStars larger than about 0.05 to 0.07 solar masses contract, getting hotter and hotter, until their cores are hot enough to begin burning hydrogen. When a star "turns on" its hydrogen-burning phase, we say that it has reached the main sequence, and is a true star, not a protostar, brown dwarf, or planet. The main sequence is a line of stars plotted on the HR-diagram, which represent stars which are burning hydrogen, fusing it into helium. The fusion process in the core releases heat and light, supporting the star against further gravitational collapse, and making it shine. Stars spend most of their life in one spot on the main sequence. Very massive stars live at the top of the main sequence, shining very blue and very bright, while low-mass stars are dim and red. The sun is between these two extremes. \n\nEventually, the hydrogen in the core whose fusion supports the star begins to run out. The core becomes mostly helium (the product of hydrogen fusion), and hydrogen burning moves out away from the core, forming a burning shell around the core. When this happens, the core begins to collapse again, but the outer regions of the star are pushed outwards. The star becomes brighter and cooler. This is the Red Giant stage. When the sun reaches the Red Giant stage, 5 billion years from now, it will likely grow to engulf Mercury, Venus, and the Earth. \n\nIf the star has little mass, it may end its life here, throwing off its outer layers, creating a planetary nebula out of its atmosphere, and a hot, dense "white dwarf" out of its core. The white dwarf shines only by residual left-over heat, and will eventually fade into a mere cinder. Cores of stars at least half as massive as the sun, however, will eventually collapse and heat enough to start burning helium in their cores. Once helium-burining starts, the star decends the giant branch again, reverses its swelling a bit, and lives happily fusing helium in its core, and hydrogen in a shell around the core. \n\nThen the giant dance begins again. The core helium runs out, and the star once again becomes a red giant. Stars like the sun get off the bus here, and become planetary nebulae and white dwarfs. Heavier stars begin burning carbon. This happens over and over again with heavier and heavier elements. The star ascends and descends the giant branch many times. Lighter stars that don't get hot enough in their cores to burn the next element become planetary nebulae and white dwarfs. Stars that are heavy enough eventually heat their cores enough to begin the next stage of burning and descend the giant branch for a while. For each element, the process is quicker and quicker. A star might burn Hydrogen on the main sequence for billions of years, but once this process gets to, say, silicon, the star might burn silicon for only a few days. \n\nA very massive star, more than 5-10 times solar mass, will ascend and descend the giant branch many times, until the star is ready to burn iron. But iron fusion doesn't release energy; it sucks it up. So what happens is that the star is ascending the giant branch, its iron core is collapsing and heating, until iron is ready to fuse. As soon as it does, though, it absorbs all of the heat around it, chilling the core. A
159173
Many of the most interesting infrared objects are associated with star formation. Stars form from collapsing clouds of gas and dust. As the cloud collapses, its density and temperature increase. The temperature and density are highest at the center of the cloud, where a new star will eventually form. The object that is formed at the center of the collapsing cloud and which will become a star is called a protostar. Since a protostar is embedded in a cloud of gas and dust, it is difficult to detect in visible light. Any visible light that it does emit is absorbed by the material surrounding it. Only during the later stages, when a protostar is hot enough for its radiation to blow away most of the material surrounding it, can it be seen in visible light. Until then, a protostar can be detected only in the infrared. The light from the protostar is absorbed by the dust surrounding it, causing the dust to warm up and radiate in the infrared. Infrared studies of star forming regions will give us important information about how stars are born and thus on how our own Sun and Solar System were formed.
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A star is basically a giant hydrogen bomb. It sits in space for billions of years fusing hydrogen into helium, creating loads of light and heat, among other things.\n\nA planet orbits a star, and is just a piece of matter that does not perform nuclear fusion. Some of them are rocky balls (like the Earth, or Mars), while some of them are giant balls of gas (like Jupiter, or Saturn).\n\nEDIT: fungusbrains1, planets twinkle too. They don't produce their own light, but they reflect light from the Sun. Any cosmic object whose light rays pass through the atmosphere twinkles.
41532
the sun is a star because it is. There are other stars in the universe that have planets revolving around them. All the stars you see in the sky are like the Sun once you get close enough. From those stars, our Sun just looks like another star in the sky.
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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.
50650
From an astronomy standpoint...\n\nThe Sun and the planets formed out of the same protostellar material.  This protostellar material was mainly hydrogen and helium with trace amounts of heavier elements produced by past generations of stars.  Something like a shock wave of other disturbance in space causes the material to compress and become gravitationally unstable.  The contraction of the protostar begins.\n\nThe majority of the material formed the Sun the rest of it was essentially stretched out in a disk.  Local gravitational unstabilities over time coalesce to form clumps of matter in the disk.  These clumps of matter are the protoplanets.  Again over time these clumps sweep out material in the disk of the solar system and build to large masses that are the present day planets.   \n\nThat's planet formation in a nutshell...at least that's how astrophysics sees the formation of Earth like planets.
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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 star is a big mass of gas. It originated as a hydrogen cloud  that started contracting because gravity pulled it together. When this happens the interior gets denser and hotter. Dense enough and hot enough for fusion reactions to start. The latter produce heat and light that pushes outwards.\n\nThe result is an equilibrium between gravity and the light radiation. The star stabilizes and stays stable for billions of years. The sun is in this stage.\n\nHowever, when the hydrogen is burnt up, the outward pressure is taken away and gravity takes over again. If the mass of this burnt out star is big enough, then there is nothing to counteract gravity.\n\nThe mass of the star will be more and more concentrated in a smaller and small volume. Gravity at the surface will become so strong that not even light can escape from it. \n\nThat is a black hole.
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.
1952
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.
1157832
Stars need hydrogen, period. The fancy name for what happens in the star is thermonuclear fusion, which just means that two hydrogen atoms are fused to make helium, and in the process release a lot of light and energy, allowing the star to shine. So, you know how when you pump up a bike tire, the pump gets hot? That's because you're compressing a fluid (in the case of stars it's hydrogen) and when you compress a fluid the fluid heats up (in this case it's the air heating up the pump). This heating up has to reach 25 million degrees before a star will shine, and the "pump" is gravity in this case. so a star has to have a lot of hydrogen from which to form if it's going to become hot enough to go into thermonuclear fusion.