In the core of the star, hydrogen is being fused into heavier elements. This provides a force to prevent the star from collapsing into itself. Eventually though (millions and millions of years having passed), the hydrogen in the core runs out and no more energy can be produced. The star swells up into a red giant and depending on its mass becomes a supernova or a white dwarf.
Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy before fading from view over several weeks or months. During this time, a supernova can radiate as much energy as the Sun could emit over its life span. The explosion expels much or all of a star's material at a velocity of up to a tenth the speed of light, driving a shock wave into the surrounding interstellar medium.
The material in a white dwarf no longer undergoes fusion reactions, so the star has no source of energy, nor is it supported against gravitational collapse by the heat generated by fusion. It is supported only by electron degeneracy pressure, causing it to be extremely dense. A white dward is very hot when formed, but since it has no source of energy, it will gradually radiate away its energy and cool down. This means that its radiation which initially has a high color temperature, will lessen and redden with time. Over a very long time, (again, millions and millions and billions of years) a white dwarf will cool to temperatures at which it is no longer visible and become a cold black dwarf. None of these are said to exist yet.
In the core of the star, hydrogen is being fused into heavier elements. This provides a force to prevent the star from collapsing into itself. Eventually though (millions and millions of years having passed), the hydrogen in the core runs out and no more energy can be produced. The star swells up into a red giant and depending on its mass becomes a supernova or a white dwarf.
ReplyDeleteSupernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy before fading from view over several weeks or months. During this time, a supernova can radiate as much energy as the Sun could emit over its life span. The explosion expels much or all of a star's material at a velocity of up to a tenth the speed of light, driving a shock wave into the surrounding interstellar medium.
The material in a white dwarf no longer undergoes fusion reactions, so the star has no source of energy, nor is it supported against gravitational collapse by the heat generated by fusion. It is supported only by electron degeneracy pressure, causing it to be extremely dense. A white dward is very hot when formed, but since it has no source of energy, it will gradually radiate away its energy and cool down. This means that its radiation which initially has a high color temperature, will lessen and redden with time. Over a very long time, (again, millions and millions and billions of years) a white dwarf will cool to temperatures at which it is no longer visible and become a cold black dwarf. None of these are said to exist yet.
(Wikipedia source)