First black hole photographed!

[understatement]

I literally have no clue on any astrophysicist material but --

Cheers!!!


~~~humans, 4/10/19

[Fyraltari]

Basically, the larger a telescope is the better it is* but due to how light interferes with itself, if you place telescopes away from each other and do a ridiculous amount of math, you can get the same result as if you had a telescope as wide as they at far apart.
So using eight ‘scopes all over the world scientists were able to create what amounts to a Earth-sized telescope and pointed it at the center of a galaxy 50 million light-years away.
Allowing us to get a picture** of what the black hole at its center looked like 50 million years ago.

The existence of black holes was predicted by the Theory of General Relativity (something that bothered Einstein immensenly, or sonI have heard). But until now we had never had direct confirmation of the existence of these physics-defying monstruous beauties that will one day gobble the whole Universe, so there was a chance we had gotten that *wrong*.

I hear they’re going to look at our own galactic center, Sagittarius A, next.

*Simplifying here, obviously.
** Sorta, we’re looking at the contrast between the black hole and the non-black matter around it.

[Lord Torath]

Here's a link to a Bad Astronomy article discussing the image. And a bit about black holes in general.

I hear they’re going to look at our own galactic center, Sagittarius A, next.

They actually already looked at Sagittarius A*, but the light (it's all light) it puts out is more variable and not as stable as the M87 black hole, so it's harder to image.

Fun fact from the article above: M87's central black hole (the one in the photo) is 1600 times wider than Sagittarius A*, and about 2000 times farther away, so it looks about the same size - roughly equivalent to a black marble wrapped in a glowing rubber band placed on the near side of the moon (also from the linked article).

[zimmerwald1915]

They actually already looked at Sagittarius A*, but the light (it's all light) it puts out is more variable and not as stable as the M87 black hole, so it's harder to image.

Also, we face M87 almost dead-on to the accretion disc, while we're at more of an angle to Sag A*, so the way the black holes lens their discs creates different images (Sag A*'s has been released by now). M87's is prettier and somewhat easier to comprehend, so it gets to be the public face of the thing.

[Lord Torath]

And, as always, Randall Munroe gives us a sense of scale.

[Yora]

On a video someone asked how much time dilation there would be near such a big black hole.

Running some numbers through Wolfram Alpha, I got a time dilation near the event horizon of about 1:100. Which seemed rather weak at first.

However, we know that because of how the radius of the Schwazshield Radius is proportional to the mass of the black hole, tidal effects at the event horizon are weaker the more massive the black hole is.
Both tidal effects and time dilation are caused by gravity. Am I correct in my assumption that the time dilation at the event horizon of larger black holes is weaker than at that of smaller black holes?

[Radar]

On a video someone asked how much time dilation there would be near such a big black hole.

Running some numbers through Wolfram Alpha, I got a time dilation near the event horizon of about 1:100. Which seemed rather weak at first.

However, we know that because of how the radius of the Schwazshield Radius is proportional to the mass of the black hole, tidal effects at the event horizon are weaker the more massive the black hole is.
Both tidal effects and time dilation are caused by gravity. Am I correct in my assumption that the time dilation at the event horizon of larger black holes is weaker than at that of smaller black holes?

Actually no, time dilation and tidal forces are not tied like that. While the latter become insignificant for large black holes, the former still has a singularity at the horizon. This is connected to the fact that one cannot see anything actually reaching or crossing the event horizon - for the outside observer the falling body simply becomes effectively frozen in time with the incoming signal becoming more and more redshifted until it is too weak to be observed at all.

[0wca88]

Freeman is watching.

[halfeye]

Actually no, time dilation and tidal forces are not tied like that. While the latter become insignificant for large black holes, the former still has a singularity at the horizon. This is connected to the fact that one cannot see anything actually reaching or crossing the event horizon - for the outside observer the falling body simply becomes effectively frozen in time with the incoming signal becoming more and more redshifted until it is too weak to be observed at all.

Yeah, I'd gathered that the concensus is that time dilation = 100% at the event horizon. That seems to mean it takes infinite time for the singularity to form. Which means that something is incorrect in the theory of black holes inside the event horizon, but since we can't see inside, it's not really relevant to us.

[Radar]

Yeah, I'd gathered that the concensus is that time dilation = 100% at the event horizon. That seems to mean it takes infinite time for the singularity to form. Which means that something is incorrect in the theory of black holes inside the event horizon, but since we can't see inside, it's not really relevant to us.

Actually it is slightly more subtle, since time dilation is singular only in a reference frame stationary to the center of the black hole. If one considers freefalling reference frames, things can cross the horizon in a finite time - it's just that noone from the outside will ever see it.