Black Hole Observations: What Changed?

[homerwho]

TL;DR

Black hole observations

Hello--
I have a question about space observations. It was only 4 or 5 years ago that I was taught that nothing could escape a black hole. More recently I have seen information and images of black holes. What has changed that now we have black hole obseravtions. Most recently, a black hole collision that I read.
Thanks

 

[Ibix]

Black holes are typically surrounded by an accretion disc, matter spinning round it as it falls in. Internal collisions in the accretion disc heat it up and it glows, and we can see that glow - although we've only managed to do so once so far. The Event Horizon Telescope picture is of the accretion disc of a super-massive black hole. The black bit in the centre is the hole itself, which you can basically see because it's obstructing the light from behind it (it's a little more sophisticated than that, but that's the gist of it).

Separately, recently we've built instruments that detect gravitational waves and not electromagnetic radiation at all. These devices have detected the gravitational wave signatures of a few colliding black holes and neutron stars. In this case, two colliding black holes spin rapidly around each other and the resulting complicated and time-varying curvature of spacetime emits little "ripples" of curvature that we pick up. The source of these ripples is the gravitational field outside the black holes, not the black holes themselves.

So what we are detecting is stuff outside black holes, but very closely associated with black holes and not explicable by any other astronomical object we are aware of. Nothing can escape a black hole, you are correct, but we can see their effects anyway.

 

[davenn]

Summary:: Black hole observations

More recently I have seen information and images of black holes.

and it was black ... wasn't it ? because nothing escapes the black hole

The black hole is the black bit in the middle of the "doughnut"
The orange/yellow ring is the glow from the accretion disk that @Ibix speaks of

What has changed that now we have black hole obseravtions.

Nothing has changed, you misunderstood what you were looking at/reading

@Ibix gave a good account in the previous post Dave

 

[sophiecentaur]

The orange/yellow ring is the glow from the accretion disk

Actually, it is a false colour representation of the effect of the black hole on passing microwaves. See this link for a picture of the Radiotelescope array that was used. I think it was a shame that they used red / yellow colours because people naturally assumed it was a regular photograph. This caused a lot of misunderstanding.

 

[davenn]

Actually, it is a false colour representation of the effect of the black hole on passing microwaves. See this link for a picture of the Radio telescope array that was used. I think it was a shame that they used red / yellow colours because people naturally assumed it was a regular photograph. This caused a lot of misunderstanding.

yeah, that's was all discussed in another thread at the time. I know the colours are false colours as previously discussed, but the basics are that it is the radio emissions from the accretion disk region

 

[phinds]

What has changed that now we have black hole obseravtions.

As davenn said, nothing.

 

[sophiecentaur]

yeah, that's was all discussed in another thread at the time. I know the colours are false colours as previously discussed, but the basics are that it is the radio emissions from the accretion disk region

I was sure I knew you knew. But it really is important that those images should be accompanied with some sort of caveat to counteract the temptation to think of them as real colours. After all, without actually knowing, those rings of colour could very easily be interpreted wrongly. (And they are, on a daily basis)

As davenn said, nothing.

We should be careful here, too. Nothing has actually changed as a result of our ability to assert (to a reasonable level of certainty) that the Big Bang is the right version of history and that goes for most of Cosmology. There are a lot of Angels on Pinhead studies which are intellectually satisfying but which will never put bread on the table or cure Civid-19.

I think that some sort of proof about the presence and extent of black holes is actually worth a lot more than "nothing". But then, solving the Guardian Crossword is not actually worth a lot either, in many opinions.