Today we will be talking about dwarfs of the star family.
The Steller core remnants composed mostly electron-degenerate matter. Their mass is comparable to Sun but their size and volume are comparable to Earth.
They are faint and their faint luminosity comes from the emission of stored thermal energy inside them as they were one core of a star, after all.
White dwarfs are the final evolutionary state of those stars which don't have enough mass to become a neutron star at the end of their lives. Those stars having mass not more than 10 solar masses become a white dwarf. As they are faint compared to other star types they are very hard to detect even with powerful telescopes. One way to find them is to look for stars with unexplained back and forth motion which suggests that the star has a massive companion and if you see a faint, dim object near the star, it's more likely a white dwarf.
The brightest star in the night sky Sirius or Sirius A have a white dwarf companion, we call it Sirius B., In fact, Sirius B is the nearest white dwarf to Earth.
Despite the fewer number of white dwarfs we found, 97% of stars in our galaxy will end up as white dwarfs including our Sun. Because 85% of stars in the galaxy are small red dwarfs and rest 10-12% out of 97% stars are our Sun-like yellow dwarfs. And the reason why we haven't found so many white dwarfs is, our Universe is still not old enough to have many white dwarfs, even with the age of 13.7 Billion years but red dwarfs can live astonishingly not Millions or Billions but more than 10 Trillion years, way longer than the current age of the Universe.
White dwarfs don't fuse atoms in their core rather they get their heat and luminosity from the stored thermal energy inside them but don't get fooled, they are amongst the hottest objects in the Universe, up to 40 times hotter than our Sun. They can shine for trillions of years and on the way, they lose their stored thermal energy but as space is mostly vacuum, heat can't be transferred by conduction, the only way heat can escape is through radiation and this way takes a lot of time. They make trillions of years to cool down. But eventually, they cool down and become a black dwarf. They take so long to cool down, Universe still doesn't have any black dwarfs. And according to some estimates, they can shine 10 billion times longer than the current age of the Universe has existed.
How white dwarfs form?
When stars less massive than 10 solar masses, exhaust hydrogen in their core, they begin to fuse helium to heavier elements. While doing so, they shed their outer layers. In the end, more than 50% of the star's mass is scattered into space as an eye flattering planetary nebula. The name is little misleading, the planetary nebula has nothing to do with planets but they do look spectacular and they can be Millions of kilometers wide. But what we are looking for can be found in their center, a white dwarf.
The white dwarf is now as big as earth but still contains half of the star's mass. A white dwarf is so massive that their one Tablespoon will weigh as much as a heavy car.
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