Why is stellar ash found in the core of a White Dwarf so dense?

In summary, a white dwarf is the core of a star made up of dense stellar ash due to the loss of heat and release of gravitational potential energy. The Pauli exclusion principle limits the density of the gas, preventing it from getting arbitrarily high. This is known as degeneracy pressure. The high density of the core is a result of natural processes extracting energy and leaving a lower energy waste product.
  • #1
avito009
184
4
A normal star's core consists of Hydrogen but a white dwarf is itself the core and it consists of stellar ash. So the degeneracy pressure is exerted when this stellar ash becomes very dense (In other words when the white dwarf becomes very dense). Am I right?

The density of a white dwarf is so much that a small cup of white dwarf material would be equal to the weight of 25 elephants. But why is the stellar ash so dense is another question?
 
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  • #2
It is natural for a self-gravitating gas to get denser and denser as it loses heat. The lost heat causes contraction, and the contraction causes the release of gravitational potential energy, which replaces the lost kinetic energy by even more kinetic energy than before. So as any such object loses heat, it will get denser and have more kinetic energy. This process would normally not end, so the density would get arbitrarily high, as occurs in a supernova that creates a black hole. But quantum mechanics has the Pauli exclusion principle, which means that no two electrons can be in the same state. That limits how dense the gas can get, because after it loses enough heat, the gas approaches its quantum mechanical ground state, and can lose no more heat. So ironically, you do not need quantum mechanics, or what is often called "degeneracy pressure" (not a very good term), to understand why the density is so high-- you need it to understand why the density does not get any higher.
 
  • #3
All natural processes extract energy from their environment and leave a lower energy waste product. It's called entropy. The reason the core of a star has high density is because even its gravitational potential energy has been exhausted.
 

1. Why is stellar ash found in the core of a White Dwarf?

Stellar ash refers to the leftover material from the nuclear fusion process that occurs in the core of a star. When a star runs out of fuel, it can no longer sustain its nuclear fusion reactions and begins to collapse. This collapse causes the outer layers of the star to be expelled, leaving behind the dense, hot core which we see as a white dwarf.

2. What makes the core of a White Dwarf so dense?

The core of a white dwarf is so dense because it is composed of highly compressed material. As the star collapses, the gravitational force becomes stronger, causing the particles in the core to be squeezed tightly together. This compression increases the density of the core, making it incredibly dense.

3. How does the density of a White Dwarf compare to that of our Sun?

The density of a white dwarf is much higher than that of our Sun. While our Sun has a density of about 1.4 grams per cubic centimeter, the average density of a white dwarf can range from 1 ton per cubic centimeter to over 1 million tons per cubic centimeter. This is due to the extreme compression of the core and the absence of the outer layers of the star.

4. Is the density of a White Dwarf uniform throughout its core?

No, the density of a white dwarf is not uniform throughout its core. As the star collapses, the outer layers are pushed inward while the inner layers remain relatively unchanged. This creates a density gradient, with the outer layers being less dense and the core being incredibly dense.

5. How does the density of a White Dwarf affect its properties?

The high density of a white dwarf is what gives it its unique properties. It is incredibly hot, with temperatures reaching up to millions of degrees, and it is also very luminous. The high density also puts immense pressure on the electrons in the core, causing them to behave differently than they would in normal conditions. This results in the formation of a degenerate electron gas, which is responsible for maintaining the white dwarf's structure and preventing it from collapsing further.

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