Event Horizon Telescope image of M87

[Vekseid]

Paper here

The Jet of M87 is thought to be tilted away from us by about 17 degrees, and if it originates at the black hole as is thought, would be at 72 degrees to the right from the top of this image (minute hand at 12 minutes past the hour on a clock face).

This would imply we are looking towards this thing's south pole - rotating clockwise from our perspective. At a 17 degree tilt, the approaching side would still be approaching us at up to 30% of the speed of light.

The black region itself isn't the event horizon, but rather the shadow. The shadow is what you don't see because light gets warped to fall into the horizon rather than reach an observer. At a distance, its radius is about 2.6 times the radius of the event horizon, with the black region being about 100 billion kilometers across in this image.

Not that you want to get that close, the parts you can see range between 3 to 6 billion Kelvin. Is somewhat hot.



They're still analyzing the Sagittarius A* data, which would appear a bit larger, but because it is so much closer, had worse weather, and is obscured by so much dust, it will take longer to process.

[Vekseid]

https://www.youtube.com/watch?v=9DILtg_9dcU

Reference video : )

[stormwyrm]

I hope we'll see something that General Relativity gets not quite right. It's in such very strong gravitational fields that we'd expect discrepancies from the theory to start appearing. There hasn't been any really big advances over the Standard Model and GR, and we know that those theories are definitely incomplete. Hopefully they get enough data for an empirical test that can verify or rule out some variations of String Theory. Other than this the only other beyond Standard Model physics these days is in neutrinos.

[midnightblack]

You'd probably have to go the opposite route to test GR's limits. Intense fields over quantum-scale distances. I'm not really in touch with what's going on there these days, but I do recall some experiments some year back in the range of atomic spectroscopy where they wanted to check if gravity has any impact. They didn't find anything, so it's likely even smaller scales are required.

I'm not sure who takes String Theory seriously anymore. Neutrinos are fun and a possible key towards unlocking new knowledge, but once again, at least to the extent that I am aware of, you require some experimental facilities that are currently beyond reach in order to test the really groundbreaking stuff (neutrinoless double beta decay without requiring a century of observation and so on and forth). There's the search for dark matter as well, but that's even more prohibitive.

[Beorning]

... I'm still saying it's a hellgate. 

[Zaphod]

This is the genius MIT student behind the imaging algorithm which is really at the heart of this breakthrough. She's also cute.

https://youtu.be/BIvezCVcsYs

[stormwyrm]

You'd probably have to go the opposite route to test GR's limits. Intense fields over quantum-scale distances.

But isn't that exactly what we can potentially get by imaging the event horizon this way? What we're seeing are the effects of the direct interaction of matter and radiation with the black hole, and those are at their heart quantum phenomena. I imagine a lot of interesting papers may soon come out exploring these aspects. I see that this kind of observation can already rule out many extensions and alternatives to GR that posit that black holes don't exist or are actually some other type of object. The event horizon seems to be quite real, and it isn't a hard surface either, since infalling matter would emit infrared if it were a solid surface, so alternative theories that do predict such things are falsified. So far, it seems the other predictions general relativity has made about black holes have not been falsified by these observations. Einstein still emerges victorious even at this most stringent of tests.

Here's a nice article about all this by an actual astronomer: https://www.forbes.com/sites/startswithabang/2019/04/10/black-holes-are-real-and-spectacular-and-so-are-their-event-horizons/

[Beorning]

I have possibly stupid question: how big is that thing, actually?

[Vekseid]

I hope we'll see something that General Relativity gets not quite right. It's in such very strong gravitational fields that we'd expect discrepancies from the theory to start appearing. There hasn't been any really big advances over the Standard Model and GR, and we know that those theories are definitely incomplete. Hopefully they get enough data for an empirical test that can verify or rule out some variations of String Theory. Other than this the only other beyond Standard Model physics these days is in neutrinos.

I think M87 is too far away for this. Particles reaching us from there will have been slowed down too much.

The black hole in the center of our galaxy is a better candidate for this, despite the current greater difficulties in observing.

This is the genius MIT student behind the imaging algorithm which is really at the heart of this breakthrough. She's also cute.

There were three algorithms, my understanding is her work was focused on finding a way to reach a consensus between said algorithms.

Her enthusiasm is infectious.

I have possibly stupid question: how big is that thing, actually?

There are a lot of different answers to that question. It is an anomaly concentrated on a mass of ~6.5 billion solar masses. It doesn't have a size, so much as the various properties around it exist at certain radii from the center.

The black region - the shadow where light can't reach us unless emitted from inside - is 100 billion kilometers across, give or take ten percent or so, and is very nearly proportional to the black hole's mass. It warps and changes shape due to its spin, but said spin is enormously hard to analyze from this image. Much of the paper is actually devoted to trying to determine said spin.

The event horizon is smaller than this, at most ~38 billion kilometers across, but the faster the black hole spins, the smaller it gets. The models for analyzing spin are apparently highly dependent on the accretion disc's magnetic field, so we're not exactly sure how fast it spins yet, and accordingly, how big the event horizon is. Analysis has only just begun, and even still, this is based on only four days of data.

[Beorning]

Hmmm. Help me out here, then: if the event horizon is 38 billion kilometers across, then how does it relate to the size of the Solar system? Is it bigger, smaller?

Just trying to get some sense of scale here...

[Vekseid]

Neptune's orbit is ~30 AU, or ~9 billion kilometers in diameter - about 1/10th the width of the black region there.

[stormwyrm]

Hmmm. Help me out here, then: if the event horizon is 38 billion kilometers across, then how does it relate to the size of the Solar system? Is it bigger, smaller?

Just trying to get some sense of scale here...

Neptune's orbit is only about 9 billion kilometres across. The Kuiper Belt, where minor planets like Pluto and many small bodies come from, is only some 15 billion kilometres across. The heliosphere, where the solar wind dominates over the stellar winds of nearby stars, is something like 34 billion km across. So yeah, 38 billion km is bigger than the whole solar system, for some ways of defining its boundaries.

[Beorning]

And I used to think that black holes were only star-sized! 

[stormwyrm]

And I used to think that black holes were only star-sized! 

Actually, stellar black holes, like the Cygnus X-1 black hole that was the first one detected, are really quite small. Cygnus X-1 is 14 times the mass of the sun, and its event horizon is at most 88 km across, even smaller if it's spinning. A black hole the size of our sun would have to be around 235,000 solar masses. That size of of black hole is generally seen in the centres of dwarf galaxies. There's also another black hole of something like that mass in the core region of the Milky Way not far from the supermassive Sag A* at the very centre, probably the central black hole of a dwarf galaxy that merged with our galaxy long ago.

[Beorning]

Hm. So, which black holes are more common? The small ones or the big ones?

Also, speaking of black holes, here's an immortal bit of dialogue from from a Star Trek comic book:



The education of Star Fleet officers is surely... broad 

[Vekseid]

Nearly every galaxy has a supermassive black hole, some (Andromeda included) have two, as a result of galactic mergers.

Our own Milky Way is thought to have a hundred million stellar-mass black holes, but it's hard to know for sure. They're obviously more common, though.