by What will we do and where will we go during the end of the Universe? That's the question we don't need to worry about now as such an event might not happen in our existence. But when we ponder over that question, we might actually find White Dwarfs are the best place to go during the end of the Universe. The White dwarfs were found to exist for several billion years, which is forever for a human time scale. So what are White dwarfs and can humans survive there?
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| The Sirius A (on the left) with its tiny White Dwarf Star Sirius B |
What are White dwarf Stars?
The White Dwarfs are the remains of the Stars after the fuel of the star is completely exhausted and the core of the star is blown away into space. They are usually smaller than our planet, but they are very massive in terms of density. For example, one teaspoon of the white dwarf has the mass of an average car. They usually live longer, it is estimated that a White dwarf could live billions and billions of years, which is astronomical compared to the human lifetime. The White dwarfs could not release the heat stored in them via conduction as there is no medium to conduct heat in space and so the only way to release the heat is via emitting the radiation. But releasing the heat via radiation takes a long time to burn up the fuel remaining in them and so they might live beyond the end of the Universe.
A typical white dwarf has the same amount of carbon and oxygen as our Sun but it is just the size of the Earth. It might be luminous but it is definitely hotter (25,000 K). In 1910, the first white dwarf was recognized in space and so far eight white dwarfs are identified in the neighbouring star systems. The lifetime of a white dwarf is usually higher than the formation of our universe and it can last for hundreds of billions of years. The nearest white dwarf was Sirius B which is estimated to be at a distance of 8.6 billion light-years. After the death of the star, there will be no more fusion reactions happening on the white dwarf star.
The Formation of White dwarfs
The demise of a Star gives birth to the White dwarfs. The Stars are usually held in balance by two forces: the gravity of the star and pressure applied by the gas outwards. When the star runs out of fuel and there are no more fusion reactions happening on the star, the balance is broken and the star inflates and forms the red giants made out of the core of the dead star. When the red star evaporates, only the core of the star is left behind and the core becomes the white dwarf containing all the heat inside of it. When the core of the star becomes unstable, the core collapses further creating a neutron star or even a black hole. The elements present in the core like helium, carbon and oxygen prevents the further collapse of the white dwarf.
Now the White dwarf settles out, the heat stored in the core is trapped inside the surface of the star. The heat is slowly released via radiation over the next several tens or even hundreds of years and the star cools down gradually. When the time comes it will die as nothing lasts forever. Several billion years after the birth of the White dwarfs, the heat stored in the star is completely radiated and now it will fade away in the cosmos creating a black dwarf. But so far no black dwarfs have been observed in the universe maybe because the universe isn't old enough to allow the formation of black dwarfs. So can they hold life on the planets around it?
Can White Dwarf Stars support life?
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| Illustration of planet WD-1856 b orbiting a dim White dwarf. Credits: NASA's Goddard Space Flight Center |
