In this topic I want to collect all the information that can be found about black dwarfs and discuss what they would look like. The goal of this small project is to make black dwarf artwork.

We already had a small discussion about this in this topic:
http://www.solarvoyager.com/forum/forum_posts.asp?TID=2413&a mp;PN=1

Ok lets start with a small description:
A black dwarf is currently a theoretical object in our universe.  Our universe has not existed long enough to sustain the time for a black dwarf to form. A black dwarf is the remains of a sun-sized star which has evolved to a white dwarf and subsequently cooled down such that it no longer gives out radiation. Instead of saying it is the end of that star it is really the beggining of a new star. Think of a black dwarf as a radioactive core, it will take extreme amounts of time to cool.  A black Dwarf may be the size of the US, but it is very dense considering it used to be the size of the sun.  Now they are theoretical, but Billions of years from now they WILL exist.

Hi Betelgeuze, yep, lets try this post here.  We can determine if folks can find it in a few days.

I'll add my thoughts:  According a few sources, The black dwarf is the end stage of a dwarf star like our sun.  A sun size star will not nova, but will grow into a red giant, reduce in size to a white dwarf feeding on itself, cool off to a brown dwarf and finally de evolving into a black dwarf some 100 billion years from now and remain that way until the end of the universe that is providing the universe survives that long. Anybody have a different theory on this

Now what will it look like, that depends on what elements the black dwarf is composed of. Any theories on this?

Could a black dwarf become a diamond--I don't know, a diamond is made up of carbon molecules.  Any theories?  Jan

hmm Ive been searching for answers but I cant find anything new. You always find the same information, I think Im going to contact an expert (but who?)

If you're going to depict a black dwarf, you might want to consider its environment. Here's some things to consider/research further.

Presumably if you're going to illustrate a black dwarf you'd need some other light source in the system, as black dwarfs don't give off their own light (hence the name) - and a black sphere against a black background isn't all that exciting. The likely candidates for the light-source are a red dwarf (the only stars which stand a chance of lasting over 100 billion years and still be fusing) or a white dwarf which hasn't cooled down yet.

If star formation has stopped (and in the Milky Way this may well be the case - the collision with M31 in ~3-5 billion years' time will probably trigger a wave of star formation that will use up most of the gas in the galaxy) the starfields will be very sparse - only red dwarfs will still be on the main sequence (and consider how many of those you can see in the night sky of Earth without a telescope: none)... there may be the occasional red giant, but even these would be rarer than today. Nebulosity would also be quite dim if there is any, though you might see one or two "planetary nebulae" from the dying stages of the last stars.

Hope that's useful to you.

Thanks chaos syndrome, very usefull information.

There may be some possibillity of confusion here.  A white dwarf will cool through orange, red, and brown to black, but this type of "brown dwarf" is far different than the more usual use of "brown dwarf" for a gaseous object more massive than a gas giant and less massive than a star.  The two types of brown dwarf will look vastly different.

On the subject of old, cold white dwarfs, does anybody know where data on their cooling rate can be found online?  In other words, given a mass of x sols and an age of y years, what will the surface temperature be?  This would be of interest to people illustrating systems today, as white dwarfs now come in ages up to at least several billion years.

Further information - according to WikiPedia, red dwarfs do not go through a red giant stage, "they contract and heat up until all the hydrogen is consumed" - presumably what remains after this process is a white dwarf of sorts, so the skies in 100 billion years time may be even dimmer than I had thought.

Edited by chaos syndrome

I agree that there are at least two types of brown dwarfs, one is at the beginning stage of life and will never develop beyond that stage and will just die out to a chunk of some element perhaps iron.

Another type of brown dwarf and this one would be at the end stages of its life.  This type of star could very well have been a yellow dwarf like our sun that has gone through the red giant stage, white, red, brown and eventually to the black dwarf stage. 

Oops more questions , born red dwarf, takes it's time "burning" its hydrogen, cooling off through its brown stage and fading to black. Also, black dwarfs, would there be different types depending on the mass?  Jan

 

 

 

Uh oh, semantics crisis! If you're only interested in the artistic side of things, feel free to ignore this post, if (like me) you like a good bit of pedantry, here goes:

As far as I am aware, the term "brown dwarf" is reserved for objects which undergo deuterium fusion but are not massive enough to sustain hydrogen fusion (for solar metallicity this is 13-70 Jupiter masses), e.g. Gliese 229 B. Brown dwarfs aren't really brown, they are more a dull red colour, other proposed names have been "crimson dwarfs" and "infrared dwarfs" (as they mainly radiate in the infrared part of the spectrum). Hot, newly formed brown dwarfs have spectral types M (there is some overlap with low-mass main-sequence stars), L and T.

Unfortunately a colour-based terminology has arisen for the degenerate cores of stars with masses below the Chandrasekhar limit (e.g. Sirius B), the term used is "white dwarf". In the present time, all white dwarfs are by-and-large white, as none of them have cooled down sufficiently, so the description "white dwarf" is reasonable (though it does leave the issue of what to call main-sequence A class stars). If we were living several billion years in the future, some "white dwarfs" would have cooled down far enough that the term would never have got into use!

However as the white dwarf cools, it becomes less white, and goes through the sequence of yellow, red, black. However I don't think that such a star would be called a "yellow dwarf" (as this refers to Sol-type stars on the main-sequence, usually spectral type G, but sometimes also F and K), or a "red dwarf" (which is used to describe low-mass main-sequence stars of spectral class M such as Proxima Centauri), any more than Vega (a white A-class star on the main sequence, a.k.a. a "dwarf" star) is called a "white dwarf".

Both "brown dwarfs" and "white dwarfs" eventually cool down until they reach equilibrium with there surroundings. However "black dwarf" is reserved for the (theoretical) endpoint of the cooling of a "white dwarf": a cooled brown dwarf is still referred to as a brown dwarf.

Perhaps the term "electron star" would be a good replacement for "white dwarf" - just as a "neutron star" is supported by neutron degeneracy, a "white dwarf" (or "electron star") is supported by electron degeneracy. Unfortunately, while this term probably makes sense, I don't think it will become official any time soon!

Hope that makes sense...


Edited by chaos syndrome

Hi all,

I've never heard of the second kind of brown dwarf that is created when a sunlike star fades away. From what I know, sunlike stars end up their lives as white dwarfs (that in time cool down and become black dwarfs). White dwarfs contain degenerated material that has a substantially different matter than brown dwarfs.


Have I missed something?