How the Stars Came To Be
Have you ever wondered how the stars came to be in the sky? In this article, we'll discuss the life cycle of a small star.
All the stars begin with slow accumulation of gas and dust(nebula). Gravitation attracts more material and it creates a knot.
If the knot is of sufficient density, it begins to collapse due to its own gravity.
As the knot collapses, it causes temperature and pressure to slowly increase. This converts the knot into a glowing protostar. A protostar is a very young star that is still gathering mass from its parent molecular cloud.
When the pressure and temperature are high enough, nuclear fusion occurs. This reaction generates an enormous amount of energy. While the star releases energy, its contraction slackens, and it shines brighter. This is called a main sequence star.
The main sequence star burns and shines bright until all of its nuclear fuel is consumed. The remaining matter contracts and heats up until the core collapses on itself that causes the star to expand. The outer layers of the star start to cool and this causes the star to dim, converting it into a red giant.
The outer layer of the red giant procedures a gaseous shell that glides away from the core, forming a planetary nebula.
When the star has lost all its core nuclear fuel and its gaseous shell has glided away, its core contracts into tiny, hot star called a white dwarf. A white dwarf is very dense and it continues to shine because of its remaining thermal energy.
When the white dwarf has cooled sufficiently that it no longer emits significant heat or light, it becomes a black dwarf.
The exact lifetime of a star depends on the size of the star. Extremely large stars burn their fuel much faster than smaller stars. Consequently, these large stars may only last a few hundred thousand years. Smaller stars, on the other hand, will last for billions of years, since they burn their fuel much more slowly.
When an extremely large star starts to dim, it changes into a super red giant. Upon that, a sequence of nuclear reactions occurs around the dying star, constructing an iron core surrounded by shells made of a variety of elements.
Having too much matter causes the star to explode, reorganizing it into a supernova for a short time. After a while, the core is so heavy that it cannot bear its own gravitational force. Thereupon, the core collapses, which results in the giant explosion of a supernova. If the core survives, it contracts to convert into a dense neutron star. If the core is larger than three times the mass of the sun, it contracts to convert into a black hole. A black hole refers to tightly packed matter with extreme gravity.
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