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Astronomers reveal first image of the black hole at the heart of our galaxy

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Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#81

Post by raattgift »

zeven7 wrote: post #56
kloch wrote: post #10

One of the findings they announced at the press conference is that the spin of the black hole is not aligned with the galactic plane but is tilted "towards us" so that it is viewed face on. How unexpected is that?

For quasars, don't the beams shoot out of the poles? Let's hope our nearby buddy doesn't become that active.

There is vanishingly small likelihood of Sgr A* becoming active (in the sense of developing highly luminous structures nearby it). There is little in the central parsec to feed it, and it is low in mass for a central black hole. There is a lot of astronomical hunting to be done to find the weak polar jet from Sgr A*.

We only look down on its north pole approximately. Extending the spin axis of Sgr A* could miss our solar system by thousands of light years. A polar jet, moreover, can be slightly unaligned from the extended spin axis, and over a 27 kilolightyear distance, that can be even more significant. Finally, we don't know whether the spin axis of the black hole will keep pointing roughly towards us, or whether it sweeps through (up or down) or around the midplane of the galaxy (or on what time scale such "precession", if any, occurs: for all we know, in a few years we might have an image that evidences an Earth-based view almost perpendicular to the spin axis).

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#82

Post by brandmeyer »

exhilaration wrote: post #62
kloch wrote: post #41

Earlier quoted context omitted.

It's actually one of the sharpest images ever made - in terms of angular resolution. The Sag.A* ring is about 51 microarcseconds in diameter. The EHT has a theoretical resolution of ~25 micro arcseconds. For comparison NirCam on Webb has a pixel resolution of 70 miliarcseconds (about 2800 times worse resolution than EHT). The reason it looks blurry is that the black hole features are close to the resolution of EHT so…

I also want to point out that the mass around Sagittarius A* is rapidly shifting which makes getting a sharp image still harder. From the NYT: Sagittarius A*, the black hole in the Milky Way galaxy, is a harder target. It is less than one-thousandth the mass and size of the M87 hole and, therefore, evolves a thousand times faster. The M87 black hole barely budges during a weeklong observing run, but Sagittarius A* ch…

> all while compiling an unprecedented library of simulated black holes to compare with the observations

It also sounds like this is the combination of an image-generating model hypothesis as well as the raw data itself. Ie, this is the image that the model produces which best-fits the sparse interferometry data.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#83

Post by colechristensen »

ckosidows wrote: post #30
adgjlsfhk1 wrote: post #17

Earlier quoted context omitted.

GR and quantum field theory don't work together, so at least one of them is wrong, and it would be good to figure out which and how.

You're saying this team has proven neither of them wrong in that their findings agree with GR, is that correct? Essentially, nothing new has been learned about these two theories?

GR and QFT essentially have to meet at black holes and this is where you’d expect to find an anomaly with ought to help open doors to new physics, but what we see here is that this observation seems to still obey GR just fine and a a closer look will be necessary to find any anomaly.

It might just not be possible to see anything odd without having a black hole right there to study, but there’s always hope that the next new observation will provide a clue as the previous ones repeatedly have not.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#84

Post by adgjlsfhk1 »

misja111 wrote: post #65
daniel-thompson wrote: post #21

Very interesting. The previously-released M87 image had just a single "shadow", but this one (of Sag A*) has multiple bright "lumps". Maybe it's in the linked papers which I haven't gotten to yet, but why the difference? Is it due to the observation method or does it reflect a real difference? Or both?

Yeah I was wondering the same. From the M87's images I understood that the bright part of the ring was moving towards us, that's why it was brighter. But with this explanation, how can there be 3 bright lumps then on Sag A's ring ..

I think it is just that this is an extremely noisy image.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#85

Post by the8472 »

neals wrote: post #61

So, what kept us from pointing a camera in that direction and snapping this picture up until now?

We have done so many times over the years. But their resolution is only good enough to show the stars in the vicinity, not the details of the accretion disc.

https://en.wikipedia.org/wiki/Sagittarius_A*#/media/File:Sgr...

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#86

Post by photochemsyn »

fasteddie31003 wrote: post #29

I am very skeptical of the Event Horizon Telescope (EHT) images because they are not following a scientific method that results in a true representative image of their target. In my opinion astronomy is jumping the shark with these images by making this a big PR stunt. I've looked at their methods for their earlier images and they seem to be hunting for a circle that looks like a black hole in their data. The EHT's f…

You mean, this?

https://iopscience.iop.org/article/10.3847/2041-8213/ac6615

>"Since the interferometric measurements are often incomplete in the Fourier domain, the inverse problem of reconstructing an image from the observed data set is usually underdetermined. Consequently, the image reconstruction requires prior information, assumptions, or constraints to derive a reasonable image from the infinite number of possibilities that can explain the measurements."

They seem to have gone to great lengths to address this issue, however. Multiple imaging approaches, synthetic data tests, etc.

https://iopscience.iop.org/article/10.3847/2041-8213/ab0e85/...

Why would looking at something that isn't a supermassive black hole at the center of a galaxy prove that this approach works or doesn't work? You'd have different constraints to apply. See for example VLBI measurements of quasars, which seem to employ the same kind of imaging approach. Theoretical models of quasars aren't the same as theoretical models of black holes. They seem to be using these theoretical models as constraints on data interpretation. Unless the theory is completely wrong, which seems unlikely, this looks like a valid approach.

https://arxiv.org/pdf/1701.04760.pdf

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#88

Post by Mehringotio »

zeven7 wrote: post #56
kloch wrote: post #10

One of the findings they announced at the press conference is that the spin of the black hole is not aligned with the galactic plane but is tilted "towards us" so that it is viewed face on. How unexpected is that?

For quasars, don't the beams shoot out of the poles? Let's hope our nearby buddy doesn't become that active.

The distance should be that far away that a potential spread would be relatively wide I would argue.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#89

Post by ISL »

mabbo wrote: post #5

> “We were stunned by how well the size of the ring agreed with predictions from Einstein’s Theory of General Relativity," And ten thousand physicists sighed disappointingly.

Gravitational physicist here. Every time we look in a new place and see that GR still works, it is pretty amazing.

Part of this is the fact that everyone in the field works very hard to find a crack in GR's armor, and so far it has resisted everyone.

The other part is that GR has a romantic beauty to it, both in structure and in predictions. Each time GR matches reality in a new context, the feeling is akin to watching a beautiful sunrise on a summer's morning. You've seen it before, but darn if it isn't pretty.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#90

Post by zeven7 »

ISL wrote: post #89
mabbo wrote: post #5

> “We were stunned by how well the size of the ring agreed with predictions from Einstein’s Theory of General Relativity," And ten thousand physicists sighed disappointingly.

Gravitational physicist here. Every time we look in a new place and see that GR still works, it is pretty amazing. Part of this is the fact that everyone in the field works very hard to find a crack in GR's armor, and so far it has resisted everyone. The other part is that GR has a romantic beauty to it, both in structure and in predictions. Each time GR matches reality in a new context, the feeling is akin to watchi…

It seems the common expectation is that GR is more likely to be the theory that needs to be modified the most - or more or less tossed out and replaced with a quantum theory of gravity. Is it possible that GR is just "right" and QM needs to be modified to fit into it?
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