I Can black dwarfs exist in the present Universe

[rootone]

A black dwarf is the dead ember of what once was an average star which expired as a white dwarf.
Is it possible that these may account for at least some of the dark matter?

 

[Drakkith]

No, no white dwarf has had enough time to cool down to near-equilibrium with the CMB, so they aren't expected to exist for another few billions of years.

 

[Aarav]

It is not possible to detect a black dwarf in present as they do not emit any heat or light. And universe is too young(seriously( ͡° ͜ʖ ͡°)( ͡° ͜ʖ ͡°)) for one

 

[glappkaeft]

No, no white dwarf has had enough time to cool down to near-equilibrium with the CMB, so they aren't expected to exist for another few billions of years.

Unless the current thinking has changed dramatically recently, if you go by that definition, an additional few billion years is nowhere enough time for that to happen. The shortest estimates I've seen is in the trillions of years.

 

[Drakkith]

Unless the current thinking has changed dramatically recently, if you go by that definition, an additional few billion years is nowhere enough time for that to happen. The shortest estimates I've seen is in the trillions of years.

That sounds reasonable. I wasn't sure what the time frame was, but I knew it was at least a few billion years, if not more.

 

[mathman]

Models of the early universe (H, He, Li) abundances are consistent with the amount of baryonic matter in the universe. Dark matter is estimated at about 5 times as much.

 

[rootone]

OK. So it's very unlikely that any black dwarfs exist in the Universe at it's present state.
They seem to be inevitable at some point in the future though.
What would it actually look like (assuming you had a ship able to get close to it.)
I would imagine a solid object about the size of Earth consisting of mainly water and CO2 ices.
Might have a liquid surface of Nitrogen and Helium, possibly hydrocarbons

 

[Chronos]

Old stars are like sequoia, they live much longer than the current age of the forest in which they reside.

 

[stefan r]

OK. So it's very unlikely that any black dwarfs exist in the Universe at it's present state.
They seem to be inevitable at some point in the future though.
What would it actually look like (assuming you had a ship able to get close to it.)
I would imagine a solid object about the size of Earth consisting of mainly water and CO2 ices.
Might have a liquid surface of Nitrogen and Helium, possibly hydrocarbons

The surface of most white dwarfs is hydrogen. Hydrogen can come in various states, gas, liquid, solid, and metallic. I am not sure which we would see at room temperature.

The exceptions would not last. There is a small amount of hydrogen in interstellar gas which will coat the carbon and helium white dwarfs as they cool. If a black dwarf collided with a rocky object it could temporarily have another surface. Collisions add a lot of heat.

 

[newjerseyrunner]

Unless the current thinking has changed dramatically recently, if you go by that definition, an additional few billion years is nowhere enough time for that to happen. The shortest estimates I've seen is in the trillions of years.

This wiki section has no source, so I'm not sure where the number came from, but it says the sun is expected to take a quadrillion years to get to that state: https://en.wikipedia.org/wiki/Black_dwarf#Future_of_the_Sun

 

[stefan r]

This wiki section has no source, so I'm not sure where the number came from, but it says the sun is expected to take a quadrillion years to get to that state: https://en.wikipedia.org/wiki/Black_dwarf#Future_of_the_Sun

That was for 5K. Why not use standard temp of 273.15? Or maybe when peak radiation is below visual.

 

[sophiecentaur]

A Black Cat doesn't need to be at deep space temperatures to be called black. Even 273K is a bit on the low side you can hardly see 400K. The way exponential decay works, the last few degrees make all the difference.

 

[glappkaeft]

A Black Cat doesn't need to be at deep space temperatures to be called black. Even 273K is a bit on the low side you can hardly see 400K. The way exponential decay works, the last few degrees make all the difference.

True but that is not how the word "Black Dwarf" is used in astronomy. While I never seen a "official" definition it always some variant of "emits no significant heat or light" with temperatures of near the CMB (in the far future) or fixed but very low number like 5K specified in different research papers.