This image was published just this past week and revealed at a press conference.
About 27,000 light-years away sits a massive astrophysical object, some four million times the mass of our sun, surrounded by swirling super-hot gasses. The existence of this supermassive blackhole called Sagittarius A* has been theorized for decades as astronomers observed nearby stars orbiting something invisible, compact and very massive at the center of the Milky Way. But they have never seen what it is – until now.
The effort shows the need for global science cooperation to undertake a project of this magnitude.
The announcement represents the work of more that 300 researchers at 80 institutions, including the Smithsonian Astrophysical Observatory, across the globe who turned a network of telescopes into a planet-sized observatory known as the Event Horizon Telescope (EHT).
“Our telescope has to be almost as big as the Earth,” said Vincent Fish, an astronomer at the MIT Haystack Observatory and EHT collaborator, at the event. To do that, the team connected more than half a dozen telescopes around the globe using a technique called interferometry. “By correlating their signals and studying the resulting data, we can reconstruct images of the source. The more telescopes the better.”
Note that this is not the first image we have obtained of a black hole. It is the first one of the one in our own galaxy.
EHT scientists used a similar technique to create the first images of a black hole M87*’s event horizon, released in 2019. But the supermassive black hole at the center of the Milky Way is quite different; it’s much smaller, and the gas swirls around it far more rapidly. Capturing the image was “a bit like trying to take a clear picture of a puppy quickly chasing its tail,” said EHT scientist Chi-kwan Chan from the University of Arizona.
The images of Sagittarius A* along with previous images of the black hole M87* give scientists more data to study black holes. M87* is much farther away from Earth and more than 1,000 times bigger than Sagittarius A*, which gives scientists the opportunities to compare the two.
This video compares the two black holes.
We have been able to learn so many things about the universe that it is easy to become blase and take it all for granted. When I step back a bit, I find it incredible that we who live in a tiny speck in a vast cosmos have been able to develop techniques that enable us to see into regions of space that our ancestors could not even dream about.
Scott Manley’s video about Sag A* has a stunning comparison: it shows the size of a single pixel of a Hubble image of that region of the sky, with the scale of the Sag A* image superimposed. The black hole image is a tiny dot in the middle of the zoomed-to-full-screen Hubble pixel.
The black hole images are an incredible achievement that required combining data from radio telescopes all around the globe.
They are going to try to take measurements over time and create a video of the accretion disk!
That will be quite a feat!
Rob Grigjanis says
That’s the second video by an astrophysicist which says the dark region defines the extent of the event horizon (radius Rs). It doesn’t. It defines a region with radius about 2.6 Rs.
Radius 1.5 Rs defines the photon sphere. While a photon emitted radially from the region between the event horizon and photon sphere will escape to infinity, a photon emitted tangentially (at 90 degrees to radial) will not. A photon emitted tangentially from just outside the photon sphere will orbit spirally outward until it gets to 2.6 Rs, at which point it will escape.
Rob Grigjanis says
“That’s the second video I’ve seen which…”
steve oberski says
Just watched “The Edge of All We Know” (https://www.imdb.com/title/tt11863046/):
A documentary film following the quest to understand the most mysterious objects in the universe, black holes.
Chronicles the effort to image the M87 black hole combined with work on the theoretical front -- “Hawking and his team attack the black hole paradox at the heart of theoretical physics-Do predictive laws still function, even in these massive distortions of space and time? “
@Robbo, #2: Seconded. Much anticipated. I hope I live long enough, compos mentis, to be able to enjoy such a video.
Now we need to launch a string of radio telescopes into different places along Earth’s orbit so we could have a virtual telescope 2 AUs in diameter. None of this piddly “size of the whole Earth” stuff.
Pierce R. Butler says
I watched the video specifically to learn how they pronounce “Sagittarius A*”: “Saj-A-Star”.
Nice & concise, but grossly inaccurate: at 4M solar masses, that thing must have consumed at least thousands of stars, and transformed into something vastly different, well beyond, say, the caterpillar-butteryfly metamorphosis. Yet, for typographic convenience, they picked the (nearly) most confusing and misleading name available.
The name Sagittarius A* follows from historical reasons. In 1954, John D. Kraus, Hsien-Ching Ko, and Sean Matt listed the radio sources they identified with the Ohio State University radio telescope at 250 MHz. The sources were arranged by constellation and the letter assigned to them was arbitrary, with A denoting the brightest radio source within the constellation. The asterisk * is because its discovery was considered “exciting”, in parallel with the nomenclature for excited state atoms which are denoted with an asterisk (e.g. the excited state of Helium would be He*).
Well this makes me tuatara*
Pierce R. Butler says
moarscienceplz @ # 9 -- Fascinating, though it sets a dubious precedent for us less-scientific types.
F’rinstance, it makes me want to add an asterisk to the name of Uma Thurman*…
It’ll be interesting to find out whether the 3 glowing clumps in the accretion disk are three separate clumps at different positions in space or the same clump at different points of an orbit in time. Provided it lasts long enough for that to become apparent.
I’m sure the astrophysicists have much more interesting questions to ask, which I’ll love to see answered but this is about my speed for now. 🙂
One interesting thing I’ve heard about this so far is that the poles of supermassive black holes in the centers of galaxies often don’t match the plane of rotation for the galaxy. The axis of rotation for Sagitarius A* isn’t 90 degrees from the plane of the galaxy, so far the idea seems to be that it’s closer to 30 degrees. Not sure what to make of that yet other than thinking it seems to agree with the idea that galaxies aren’t gravitationally bound together by their central black holes, no matter how massive they are. That idea doesn’t need this to support it if you have the math for it though, I just don’t so it’s useful for visualization. 🙂
Rob Grigjanis says
lanir @13: Matt Strassler addresses some questions. Shorter: no clear answers for some questions, as yet.
consciousness razor says
They would be spatially-separated clumps. I don’t recall what they had said orbital speeds during the press conference, but I’m fairly certain they can easily rule out something like the latter. (Well … “easily” is a relative term here. None of this was “easy.”) And as others mentioned above, they’re already fairly close to producing video, rather than just a still image.
Just to be clear, it’s not as “clumpy” as some might naively think either — it’s not as if what you see are some gigantic balls orbiting it or something like that. Those are just some places in the disk which show up a little brighter than other spots.
And it’s probably worth mentioning that this sort of image is also not really like a conventional photograph. Although I don’t understand a lot of the details,* it’s more like an assemblage of different possible/candidate observations superimposed with one another, having chosen the best sort of “fit” to that data based on tons of really careful analysis.
*Plus, I’m relying mostly on memory of what was said about observing the M87 black hole, since I just remember one woman going into a lot more depth about it back then. And I’m fairly sure the basic strategy hasn’t really changed.
Well, there have been radio telescopes put into high polar Earth orbit before to get far longer baselines: Japan’s HALCA and Russia’s Spektr-R were launched in 1997 and 2011 respectively. Sadly, despite work starting in the 1980s, Russia’s telescope had so many delays that it didn’t actually launch until after Japan’s had both successfully launched and shut down (in 2005, though its last really useful measurements were in 2003 before it ran out of fuel for attitude control), so we never got both operating at once.
The EHT didn’t even start operation until years after HALCA shut down, and while there was some overlap between Spektr-R’s operation and the earlier stages of the EHT, I don’t know if any Spektr-R data was involved in the earlier EHT work. Since Spektr-R had a full communications failure in 2019, it wouldn’t have been involved in any of the more recent observations anyway.
(Twenty years ago I worked at an organization that produced equipment and support for interferometry work, mostly in regards to recording and analyzing 128Mbps data streams, and I actually ended up babysitting some of our equipment at a remote site once. Some of my co-workers spent time in Vladivostok in the 1990s collaborating with the Russian scientists on their program. There’s some fascinating stuff out there. Like once you get a good fix on a quasar location, you can then calculate the relative positions of the telescopes, and use that to monitor things like the Earth’s rotation rate and even continental drift on pretty much a day-to-day basis.)