Black Hole Image - livestreamed discussion from MIT on April 12th

Janx · Apr 14, 2019

Umbran said:
Having heard a good talk about this from MIT, I wanted to go back to this question. Part of the reason they went with M87's black hole first is due to the gas and dust issue I mentioned, but there's a bigger issue...

Before they took this image, we had some measurements of how wast gas, dust, and stars were moving around these black holes. Things around M87's black hole move a little more slowly. We expect visible changes in the image to take a couple of weeks - which means that if each observation takes a day, the image is mostly static for that period of time.

Things are moving much more quickly around SagA*, and we expect the image to change over the course of days or even hours, which means that the day-long observations used would yield very blurry images. They are planning some upgrades to the system that should help with that for the SagA* observations, but they could look at M87 without them.

Thanks for the followup and for taking the time to answer these kinds of questions.

Since M87 is very far away, we're looking at how it used to be. What do you imagine it looks like now? Did everything get sucked into it? Or did life go on and everybody there is used to the big dark spot in the sky?

Morrus · Apr 15, 2019

Janx said:
Thanks for the followup and for taking the time to answer these kinds of questions.

Since M87 is very far away, we're looking at how it used to be. What do you imagine it looks like now? Did everything get sucked into it? Or did life go on and everybody there is used to the big dark spot in the sky?

It’s 55m light years away, so we’re seeing it 55m years ago. That’s not very long, relatively speaking (I think the earth is about 5 billion years old? So a factor of a hundred or so there)

So I imagine it probably looks pretty much the same. A galaxy of stars happily orbiting around a supermassive black hole like have been doing for billions of years.

You wouldn’t normally be able to see the dark spot any more than you can see the one at the centre of our galaxy. It’s only the size of our solar system. It’d be a tiny pinprick.

Umbran · Apr 15, 2019

Morrus said:
Man, that's a mind-breaking figure.

It was also wrong! Sorry. It is 6.5 billion suns, not 65 billion. Whoops! It is still ginormous. It is the largest such object known.

I tried to put it into a context to better visualise it -- so our galaxy has about 100b stars from a quick Google search (though there were different answers). If that's the case, the black hole is over half the mass of an entire galaxy!

We don't have a good handle on the number of stars in the Milky Way - estimates range from 100 to 400 billion stars.

The overall mass of the Milky Way is about 1x10^12 suns. The overall mass of the M87 galaxy is about double that.

Umbran · Apr 15, 2019

Janx said:
Since M87 is very far away, we're looking at how it used to be. What do you imagine it looks like now? Did everything get sucked into it? Or did life go on and everybody there is used to the big dark spot in the sky?

Morrus has it right.

It is 55 million light years away. 55 million years ago... we saw the first horses and primates on Earth, I think. The dinosaurs had been gone for about 10 million years.

Which sounds impressive, until you realize that the Sun... didn't notice any of that. Galaxies measure their lives in the billions of years, not in the millions. M87 likely had that black hole pretty much from it's origin, which is probably upwards of 13 billion years ago. The recent 55 million years? Not really a big deal. It is much the same now as it was 55 million years ago.

Istbor · Apr 15, 2019

Umbran said:
Morrus has it right.

It is 55 million light years away. 55 million years ago... we saw the first horses and primates on Earth, I think. The dinosaurs had been gone for about 10 million years.

Which sounds impressive, until you realize that the Sun... didn't notice any of that. Galaxies measure their lives in the billions of years, not in the millions. M87 likely had that black hole pretty much from it's origin, which is probably upwards of 13 billion years ago. The recent 55 million years? Not really a big deal. It is much the same now as it was 55 million years ago.

Man our lives are short.

Umbran · Apr 15, 2019

Istbor said:
Man our lives are short.

Yep.

Astronomy and astrophysics have some of the best perspective-inducing items known to man.

freyar · Apr 15, 2019

Umbran said:
You are seeing inconsistent measurements, because there are two different things being discussed. One is the event horizon of the black hole. The other is a "shadow" - the lensing effects of the black hole creat teh ring in the image that is much larger than the hole itself - the shadow's radius is about 2.6x the radius of the event horizon.

Just to highlight this, we're not actually seeing the event horizon. The event horizon is where light stops being able to escape the black hole if it's beamed straight away from the center, but where shining material can actually orbit the black hole and not just fall in quickly is considerably farther out. Plus there is redshifting near the horizon that makes light sources there appear much dimmer to us.

There are several nice articles for the public by a very good physicist (but a non-expert on this measurement) at the Of Particular Significance blog.

Istbor · Apr 15, 2019

Umbran said:
Yep.

Astronomy and astrophysics have some of the best perspective-inducing items known to man.

Well aside from the somber effects such discussions can have on the Human psyche, I was super excited about this image. Still am. I cannot wait until we learn more. And I am gladdened that what we surmised about Black holes appears accurate.

tomBitonti · Apr 15, 2019

freyar said:
There are several nice articles for the public by a very good physicist (but a non-expert on this measurement) at the Of Particular Significance blog.

Those are really great!

Thx!
TomB

Umbran · Apr 16, 2019

Istbor said:
Well aside from the somber effects such discussions can have on the Human psyche...

It is somber because we have an over-inflated view of our role in the Universe. When we get a bit of humility, it ceases to be so depressing, and reverts to wonderment.

Black Hole Image - livestreamed discussion from MIT on April 12th

Janx

Hero

Morrus

Well, that was fun

Umbran

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Istbor

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