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Astronomy @mander.xyz

2y ago

The largest Black Hole compared to Our Solar System

28 comments

Is there a banana for scale or does Lemmy use a different model for scale? Beans?
- I think all the bananas (and beans) are already in the picture
  
  Well, even the picture is in the picture..

And it has a density of only about 3g per cubic meter. It's not much denser than a vacuum made with a mechanical pump.
- That's the thing about black holes that always blows my mind. I don't understand how the larger a black hole is, the less dense that it is. In my mind, I always think of black holes as super dense objects containing so much matter in such a little space that the gravity is crazy strong. How can something so not dense be a black hole? It doesn't make sense to me!
  
  To be fair, the density is calculated from the event horizon, which is a somewhat arbitrary boundary. All the mass is still concentrated at the singularity which is still infinitely dense, just... a bit more so.
- Hiw stable is this kind of density? Is it going to shrink over time?
  
  Not really. If more material falls in, its mass and size increases (the volume increases faster than the mass, which is why it's so unexpectedly low density in the first place), but otherwise it just sort of sits there.
  Over the very long term, it will evaporate away by Hawking radiation. But that's a very very slow process. Like, long after everything else in the universe has ended.

- Supposedly.
  They can still rotate, so that means they're not just unidimensional points in space.
  
  Technically couldn't a ray emanating from a singularity rotate? Like, the point could have a sort of orientation without having any real measure?
  Not saying that's the case here, but I think it could happen.
- Normally black holes are considered to be everything up to the event horizon. E.g., from the Wikipedia page:
  The size of a black hole, as determined by the radius of the event horizon, or Schwarzschild radius, is proportional to the mass, M
  The term "black hole" derives from the fact that beyond a certain point light can't escape, that point being the event horizon.

That's actually smaller than I would have thought. I wouldn't have expected our solar system to even be visible in comparison.
- What the hell are you talking about, that thing is beyond comprehension.
  
  We shouldn't downvote people when they realize they have been thinking about something the wrong way and admit it.

How big is this, in real numbers?
- More than 1 AU.
  
  That's technically correct.
- About 1600 AU, according to wikipedia.

Lucky for us, it is to far away.

28 comments