Source of energy for white dwarf and neutron star

[starfish99]

I know that nuclear fusion is the source of energy for our sun and most of the other stars. Neutron stars and white dwarfs have very high surface temperatures. What is the source of their energy?

 

[stevenb]

I know that nuclear fusion is the source of energy for our sun and most of the other stars. Neutron stars and white dwarfs have very high surface temperatures. What is the source of their energy?

Just stored thermal energy with very small surface for black-body emission. Cooling proceeds relatively slowly but eventually the thermal energy is lost.

 

[starfish99]

So many billions of years from now neutron stars and white dwarves will approach a reasonable "room temperature" of 300 degrees kelvin. A neutron star will be a giant mass of neutrons. What will a white dwarf become? Will it evolve into a neutron star?

 

[Chronos]

A white dwarf will eventually fade to become a cinder [black dwarf]. This will take many billions of years. It will never become a neutron star. Neutron stars evolve from much more massive progenitor stars.

 

[starfish99]

So Chronos, will the black dwarf cinder be made of extremely dense oxygen, nitrogen, carbon, etc that doesn't exist naturally on our planet and can't be created in our labs?

 

[Janus]

So Chronos, will the black dwarf cinder be made of extremely dense oxygen, nitrogen, carbon, etc that doesn't exist naturally on our planet and can't be created in our labs?

It would made of electron-degenerate matter. Essentially, all the electrons will have been stripped from their atoms, and you have nuclei floating around in a sea of these electrons. The density of such matter would be around 10,000 kg/cm³

 

[ibysaiyan]

I know that nuclear fusion is the source of energy for our sun and most of the other stars. Neutron stars and white dwarfs have very high surface temperatures. What is the source of their energy?

Yes,you are right about the main sequence stars and the super giants.White dwarfs basically stay stable due to the electron degeneracy pressure and they are said to become a black dwarf (an object which is yet to be observed due to young age of the universe).White dwarfs have radius hence smaller surface area as a result of which thermal energy is radiated away in a very slow manner.

Neutron on the other hand are exotic,dense objects.Have an angular momentum and are able to withstand inward gravitation collapse due to neutron degeneracy pressure.

To answer your question: I believe their source of energy comes from their precursive state i.e Main sequence,Super giant stars.

Now that you mentioned their 'source of energy' who knows what else remains hidden to us beyond the stellar gases. I wonder could the accreting matter to the W.D in Type 1a be counted as a 'source of energy' ?

 

[ladykrimson]

Do we know of any black dwarf objects in existence?

 

[FtlIsAwesome]

Do we know of any black dwarf objects in existence?

A black dwarf is what a white dwarf becomes eventually because it cools.
It no longer emits light and would not be detectable this way.
The only way I can think of to detect such objects would be to measure there gravitational effects on other objects, such as in a binary system, or gravitational lensing of light sources behind the black dwarf.

As far as I know, we haven't detected any black dwarfs.

So to rephrase your question: Have astronomers detected black dwarfs by their gravity?

We have detected a white dwarf companion of Sirius by its gravity. The white dwarf is too dim to see with the unaided eye.
It has a mass roughly that of the Sun and a size of Earth. Gives you an idea how dense these things are.

 

[Janus]

Do we know of any black dwarf objects in existence?

Given the time that it would take for a white dwarf to cool into a black dwarf and the estimated age of the universe, there hasn't been enough time for any black dwarfs to form.