White Dwarf

White Dwarf

A white dwarf is a dead star of comparatively lower mass i.e. approximately 1.3 to 8 solar masses that has all its solar fuel after burning for millions of years and now is in a constant process of cooling. Its color appears white because of the heat radiated from its surface.

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 When a star has consumed all its hydrogen then combustion stops. Since nuclear fusion inside the core of the star stops therefore, the outward pressure due to this combustion declines and star starts compacting due to the enormous gravity produced by its mass. Star heats up more due to this and the rest of the hydrogen also burns in the outer layer of the star causing the outermost layer to expand. This expansion is so massive that it can eat a whole solar system comparable to that of the size of our solar system. This stage of a star is called red giant stage. Due to its large size, the surface is cooler than its core. The core of this red giant is completely made of helium which has been formed by continuous fusion of hydrogen. Since the core is covered by the outer expanded core which is still in the process of fusion, the core becomes so dense and hot that the helium in its inner most layers start turning into heavy metals. The life of this red giant is too small as compared to its life as a glowing star. When all the hydrogen of the outer expanded layer is finished, it explodes and produces a nebula which is a massive cloud of the remains of a dead star. After the explosion only the core of the star is left behind which is so dense that only a spoonful of matter taken from that core will have the mass comparable to that of an elephant. The gravitational pull of this core is very strong and if it is too massive in size then it starts attracting matter from the nearby space and its mass as well as gravitational pull keeps on increasing and it may convert into a black hole in the course of time, but if the star is a small one as our sun is then it won’t be able to reach that category and will keep cooling for trillions of years by radiating its heat. Due to this radiation, the star appears white and is known as white dwarf.

If the inner core of the white dwarf becomes too hot due to immense pressure then it explodes into a supernova which is the brightest cosmic activity in the space. If the dwarf is a smaller one then it doesn’t explode and keeps cooling for a very long period. In the present records, there is no white dwarf that has cooled completely but there are many whose age as a white dwarf is somewhat equal to the age of our universe.
Related Articles: Black hole, White hole, Exotic Star, Flipping of Solar Magnetic Poles, Space-time, Astronomical Unit, Supernova, Red Giant, Nebula

Credits: Image Source- Google images

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