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Comment by rapsey | Hacker News Reader

How would we see black dwarves?

If there were bright things behind them

The universe is young, a lot of stuff hasn't happened yet. It wouldn't be surprising if we are about the earliest life of this sort that could exist.

I thought the cosmological expansion theory of the standard model was falling apart calling into question the Big Bang theory. If that’s the case, then are we sure we have a good handle on the age of the universe?

Do you have any links where I can read more about that? That's fascinating and I wasn't aware, and I evidently am not using the right search terms to find out more

Maybe unrelated but YouTube has been throwing a lot of faux science and astronomy at me lately. Youtubers reading controversial papers presented as indisputable even when there's no scientific consensus at all on the results.

It's depressing to think about, but for many intents and purposes fake space facts are just as good as true space facts.

Especially for purposes of monetizing YouTube videos.

I believe they’re referring to the “crisis in cosmology”. I’m purely a layman, but I found some videos useful. I believe at least PBS Space-Time [1] is well regarded in physics circles (for laymen explanations.). I found the other one [2] to be more digestible though.

[1] https://youtu.be/72cM_E6bsOs

[2] https://youtu.be/0sfvQ_fsil4

Depends on your perspective I suppose. Most of the stars have already formed and star formation will slowly grind to a halt in a few billion years.

old and young universe then :)

At least, I can understand visualize the time scale of the universe a lot better than I can visual the length scale. Speed of light doesn't feel like 1/1 to humans!

A BD is still hotter than background temp, so you could maybe see faint IR, and you could initially find it as a result of its mass if there are nearby objects orbiting (although now less illuminated), or simply transitioning in front of other stars (I guess that's how they find wandering planets?).

Alternatively, map all the white dwarves, then wait long enough, then look again..

You'd probably also be able to see white dwarves that were on their way to being black (whatever the threshold is).

There's no hard threshold, the star just fades gradually from #FFF to #000.

A fully black dwarf would be so cold it would be indistinguishable from cosmic background radiation, but that's going to take at least a trillion times longer than the current age of the universe. Not just slightly longer.

Right. I'm just saying that if the are any black dwarfs (which there should not be), we should be able to find ~arbitrarily dim ones as well, down to our ability to see.

Given there are no BDs (so they are theoretical) maybe there isn't a threshold defined?

A WD will slowly cool to a BD over Trillions of years, so it's all linear. Funnily enough, they are probably every shade of red/brown in-between - but "brown dwarves" are usually reserved for objects that never where "proper" hydrogen-fusing stars, but are large enough to fuse deuterium.

Gravitational lensing, most likely.

Possibly through gravitational interactions with non-dwarf stars in the same system.

There not being any yet makes either method somewhat more challenging.

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