Stars form in molecular clouds, namely a broad region of the interstellar medium with a high density (though still less tightly when compared with a vacuum chamber on Earth). These clouds consist mostly of hydrogen with about 23-28% helium and a few percent heavier elements. Composition of elements in the cloud has not changed much since the Big Bang nucleosynthesis in the early universe.
Gravity takes a very important role in the process of star formation. Star formation begins with gravitational instability inside a molecular cloud can have a thousand times the mass of the sun. This instability is often triggered by shock waves from supernovae or the collision between two galaxies. Once a region reaches a sufficient density of matter qualifies the Jeans instability, the cloud began to collapse under its own gravity.
Based on the Jeans instability condition, the stars are not formed independently, but in a group that originated from a collapse in a large molecular cloud, then split into individual conglomerate. This is supported by the observation that many same-old star joined in a star cluster or association.
Once the cloud collapse, will occur individual conglomerate of dense dust and gas called Bok globula. Bok Globula can have up to 50 times the mass of the Sun. The collapse globula create increased density. In this process the gravitational energy is converted into heat energy so that the temperature increases. When the cloud of this protostar reaches hydrostatic equilibrium, a protostar will form in the core. Pre-main sequence stars are often surrounded by a protoplanetary disk. Shrinkage or collapse of molecular cloud takes up to tens of millions of years. When the increase in core temperature protostar reaches the range of 10 million kelvin, hydrogen in the core 'burned' into helium in a thermonuclear reaction. Nuclear reactions inside the star's core to supply enough energy to maintain the pressure at the center so that the shrinkage stops. Protostar is now starting a new life as a main sequence star.
Gravity takes a very important role in the process of star formation. Star formation begins with gravitational instability inside a molecular cloud can have a thousand times the mass of the sun. This instability is often triggered by shock waves from supernovae or the collision between two galaxies. Once a region reaches a sufficient density of matter qualifies the Jeans instability, the cloud began to collapse under its own gravity.
Based on the Jeans instability condition, the stars are not formed independently, but in a group that originated from a collapse in a large molecular cloud, then split into individual conglomerate. This is supported by the observation that many same-old star joined in a star cluster or association.
Once the cloud collapse, will occur individual conglomerate of dense dust and gas called Bok globula. Bok Globula can have up to 50 times the mass of the Sun. The collapse globula create increased density. In this process the gravitational energy is converted into heat energy so that the temperature increases. When the cloud of this protostar reaches hydrostatic equilibrium, a protostar will form in the core. Pre-main sequence stars are often surrounded by a protoplanetary disk. Shrinkage or collapse of molecular cloud takes up to tens of millions of years. When the increase in core temperature protostar reaches the range of 10 million kelvin, hydrogen in the core 'burned' into helium in a thermonuclear reaction. Nuclear reactions inside the star's core to supply enough energy to maintain the pressure at the center so that the shrinkage stops. Protostar is now starting a new life as a main sequence star.
Ref :
http://id.wikipedia.org/wiki/Bintang
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