White Dwarfs Star:
When they reach their long evolutionary end, the little stars – those up to eight times the size of our own sun – are usually White Dwarfs.
These old stars are incredibly dense. A teaspoon of material on earth will weigh like an elephant 5.5 tons. The radius of the white dwarf is usually 0.01 times the radius of our own sun, but their mass is roughly the same.
Stars like our sun melt their hydrogen into helium in their core. The white dwarf stars
are stars that have burned all the hydrogen they have used as nuclear fuel.
The fusion in the core of the star produces heat and outward pressure, but the pressure is balanced by the inward thrust of the gravity produced by the mass of the star. When the hydrogen used as fuel disappears and the melting becomes slow, gravity causes the star collapse on itself.
As the stars condense and compact, it further heats up its final hydrogen and causes the outer layer of the star to expand outwardly. At this stage, the star becomes a big red giant.
Because a red giant is so big, its heat is emitted, the surface temperature is mainly cold, but its core is still red hot. The red giants only exist for a short time – maybe only one billion years compared to the same stars that might have been burning hydrogen like our own solar billions of dollars.
The red giants
are hot enough to make helium at its core, by melting hydrogen, making heavy elements such as carbon. But most stars are not sufficient to produce the pressure and heat required to burn heavy elements, so melting and heat production are stopped.
Such stars eventually blow off their outer layers of material, which produce an inflated gas shell called a planetary nebula. In this nebula, the thermal core of the star is crushed into high density by gravity as a white dwarf fortress of more than 180,000 degrees Fahrenheit (100,000 degrees Celsius).
Ultimately – more than a few dozen or even tens of billions of years – a white dwarf cools until it becomes black dwarfs, does not emit energy. Because of the universe’s oldest stars only 10 billion to 20 billion years old, there is no known black dwarf star.
It is estimated that a long time of white dwarfs cooling can help astronomers learn more about the age of the universe.
But not all dwarf Stars will spend thousands of years cooling their heels. Those in the binary star system can have dwarfs planets a strong enough force to gather from the adjacent stars in the material. When the white dwarfs get enough quality in this way, it reaches the level known as the Chandrasekhar limit. At this point, the pressure of the center will become so large that there will be out of control fusion, and the stars will be detonated in the hot spring supernova.
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