About four and one half billion years ago our protosun was slowly collapsing under the force of its gravity. As it did this, due to the immense compression caused by gravity it became extremely hot. Millions of degrees centigrade. The more compact it got, the hotter it got. It was not alone in the sky, it was part of a community of stars and protostars that lay in the outer regions of our galaxy, the Milky Way. The proto-sun was being swept around the galaxy, along with its neighbours, at the tremendous speed of over 500,000 miles per hour - relative to the center of the galaxy. So far it had no satellites, (planets, moons, etc.) it’s gravity had sucked in most of the star dust from its vicinity for hundreds of millions of miles in every direction. It was getting close to the temperature and pressure required for a nuclear fusion reaction to occur. The protosun was like a giant nuclear hydrogen bomb waiting to be detonated. THE BIRTH AND DEATH OF STARS : A star begins its life as a cloud of mostly hydgrogen gas and dust floating in space. If something disturbs this cloud, such as a passing star, it can begin to collapse, and the gravity that is produced attract other particles of gas and dust. As the cloud shrinks, the speed at which these particles fall towards the center of the cloud causes it to heat up and glow, forming what astronomers called protostar. When the protostar reaches a certain temperature, a process known as hydrogen fusion begans, fueled by the hydrogen gas present. Hydrogen fusion creates such tremendous heat that the protostar tries to explode outward, but the powerful gravity of the gas and dust particles prevents this from happening. Instead, the protostar remains perfectly balanced between exploding and collapsing, and it becomes a star. Stars have life expectanicex ranging from a hundred or so million years to trillions of years, depending on their sizes. A very massive star uses up, or burns, its nuclear fuel very rapidly and has a relatively short life span. A star with a very low mass burns its fuel much more slowly and lasts much longer. Medium sized stars, like our sun, use up their hydrogen in about 10 billion years. Eventually, a star begins to run out of hydrogen gas and hydrogen fusion ceases. At that point, it begins to collapse again, generating even more heat. The star becomes so hot that other gases, such as helium, begin new processes of fusion. These new fusions generating such tremendous heat that the star expands greatly, becoming what is known as a red giant. While the outer layers of red giants are relatively cool, these stars are very bright because of their tremendous size. As a red giant runs out of fuel, it collapses once more. If the orginal star was relatively small, the red giant will collapse into a small, dense form called a white dwarf. A white dwarf appears very dim because of its small size, but it is hot. If the orginal star was massive, the collapsing red giant will generate so much heat that the star explodes. The resulting explosion is called a supernova and is millions of times brighter than an ordinary star. The part of the star left behind by the explosion becomes a neutron star, rapidly spinning star that is even smaller and denser than a white dwarf. If the orginal star was extremely massive before it exploded, the neutron star would also collapse and would never stop collapsing. It would become a black hole, which is so dense and has such an enoromous gravitational pull that even light cannot escapefrom it. A black hole has never been seen but would probably appear as a dark hole surrounded by a spiral-shaped halo of hot particles attracted by its gravity. Matter that falls into it can never escape. Neuton star often emit bursts of radio waves into space. Because the neutron star spin rapidly, these radio waves are detected by radio telescope as a pulsating signal, with a single pulse for every rotation. Because of these pulses, the first neutron stars discovered were known as pulsating stars, or pulsars.
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