Another black hole visualized, this one at the heart of our own galaxy

May 12, 2022 • 10:45 am

I had no idea that there was a big black hole at the center of the Milky Way, but that is indeed the case, though it seems to have been discovered not that long ago and photographed just now, as documented in the Event Horizon site below (click on screenshot).

The hole, called Sagittarius A* (or SgrA*) was discovered when several stars were orbiting around an invisible spot in the galaxy. Although black holes are themselves invisible, they can be visualized because they’re surrounded by a ring of glowing gas. The website Event Horizon Telescope (which is the group that visualized it and the first black hole) describes the finding and shows the photos, which are, after all, what we want to see. Producing them was itself a remarkable feat, as described below.  Click on the screenshot below to read:

From the site:

Although we cannot see the black hole itself, because it is completely dark, glowing gas around it reveals a telltale signature: a dark central region (called a “shadow”) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun.

We were stunned by how well the size of the ring agreed with predictions from Einstein’s Theory of General Relativity,” said EHT Project Scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei. “These unprecedented observations have greatly improved our understanding of what happens at the very centre of our galaxy, and offer new insights on how these giant black holes interact with their surroundings.” The EHT team’s results are being published today in a special issue of The Astrophysical Journal Letters..

Because the black hole is about 27,000 light-years away from Earth, it appears to us to have about the same size in the sky as a donut on the Moon. To image it, the team created the powerful EHT, which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope [1]. The EHT observed Sgr A* on multiple nights, collecting data for many hours in a row, similar to using a long exposure time on a camera.

Here you go. The site also shows, visually, how different images were averaged and combined to create this “definitive” photo (click photos to enlarge them):

Caption from website: This is the first image of Sgr A*, the supermassive black hole at the centre of our galaxy. It’s the first direct visual evidence of the presence of this black hole. It was captured by the Event Horizon Telescope (EHT), an array which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. The telescope is named after the event horizon, the boundary of the black hole beyond which no light can escape.   Although we cannot see the event horizon itself, because it cannot emit light, glowing gas orbiting around the black hole reveals a telltale signature: a dark central region (called a shadow) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun. The image of the Sgr A* black hole is an average of the different images the EHT Collaboration has extracted from its 2017 observations.  In addition to other facilities, the EHT network of radio observatories that made this image possible includes the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile, co-owned and co-operated by ESO is a partner on behalf of its member states in Europe.

You may remember that 3 years ago first image of a black hole, M87*, was released. That one, called M87*, sits at the centre of the more distant Messier 87 galaxy, and is a much larger hole—a thousand times the size of SgrA*. Here’s a picture of that “first” black hole from the NYT, with the newly added visualization of polarized light.

More from the site:

The two black holes look remarkably similar, even though our galaxy’s black hole is more than a thousand times smaller and less massive than M87* [2]. “We have two completely different types of galaxies and two very different black hole masses, but close to the edge of these black holes they look amazingly similar,” says Sera Markoff, Co-Chair of the EHT Science Council and a professor of theoretical astrophysics at the University of Amsterdam, the Netherlands. “This tells us that General Relativity governs these objects up close, and any differences we see further away must be due to differences in the material that surrounds the black holes.”

. . . . The effort was made possible through the ingenuity of more than 300 researchers from 80 institutes around the world that together make up the EHT Collaboration. In addition to developing complex tools to overcome the challenges of imaging Sgr A*, the team worked rigorously for five years, using supercomputers to combine and analyse their data, all while compiling an unprecedented library of simulated black holes to compare with the observations.

Scientists are particularly excited to finally have images of two black holes of very different sizes, which offers the opportunity to understand how they compare and contrast. They have also begun to use the new data to test theories and models of how gas behaves around supermassive black holes. This process is not yet fully understood but is thought to play a key role in shaping the formation and evolution of galaxies.

So there you go. I consider the prediction and then verification that these bizarre entities exist to be of the triumphs of the human mind. The theory began as an outgrowth of Einstein’s General Theory of Relativity, and required the work of many people. Ultimately, Stephen Hawking and Roger Penrose gave the definitive proof that black holes were a natural result of Einstein’s theory. Then they were “photographed” using radioastronomy. For his theoretical work, Penrose won half of the 2020 Physics Prize, but Hawking was dead by then or almost surely would have shared the Prize.

Here’s a happy man:

h/t: Matthew

39 thoughts on “Another black hole visualized, this one at the heart of our own galaxy

  1. The size of these monsters is truly mind blowing, especially M85. M85 is 6.5 billion times the mass of our star and Sag A* is 4 million times the mass of our star. If you were to plop M85 in our solar system its horizon would be out by Neptune, for Sag A* it would be around the orbit of mercury.

  2. I had no idea that there was a big black hole at the center of the Milky Way

    I think the current theory is that there is a big black hole at the center of *most* galaxies, because bigger gravitational things tend to either end up there or be the center around which other things gravitate.

    There was a data-based graphic a year or two ago showing the movement of stars around Sag A, where they whip through very tight curves around a center point (in time lapse, of course). This seemed to me an obvious “smoking gun” indication of a huge mass in the middle. I coulda sworn the three-blob picture you show here was a year or two old too, but I may just be remembering my blobby astronomical pictures wrong.

    In any event, better data is always great. Which reminds me, JWST…I’m still waiting! (Optimistically – that’s not a complaint.)

    1. Sometimes there are more than one black hole at the center of a galaxy. Sometimes they merge, sending out gravitational waves that we can now detect. The amount of mass and energy involved is just mind boggling.

  3. Be sure to watch Veritasium’s superb video on this. Explains how it was done, and why the image looks like it does. Some mindblowing information there.
    IMO, the best science-focused channel.

    1. Yes, see it – I especially like how he used tangible models to show the main idea – as if he was in a lecture hall. Because fancy graphics – though very useful – can be … anesthetizing, perhaps…

    2. It’s a REALLY good channel. I also enjoy PBS Spacetime (and PBS Eons) and Brady Haran’s various channels, including Sixty Symbols, Deep Sky Videos, Periodic Videos and Numberphile, among others. These latter are very interview-style, but Brady is a brilliant science video-journalist and the people he interviews are outstanding. (Though Professor Moriarty* did take mild issue with one of Veritasium’s video titles regarding the many worlds interpretation of quantum mechanics…it was fun, though).

      *That’s his real name…though he’s Philip, not James.

      1. I’ll just leave this here:

        COML 2034 — Black Holes: Race and the Cosmos

        ” Conventional wisdom would have it that the “black” in black holes has nothing to do with race. Surely there can be no connection between the cosmos and the idea of racial blackness. Can there? Contemporary Black Studies theorists, artists, fiction writers implicitly and explicitly posit just such a connection. Theorists use astronomy concepts like “black holes” and “event horizons” to interpret the history of race in creative ways, while artists and musicians conjure blackness through cosmological themes and images. Co-taught by professors in Comparative Literature and Astronomy, this course will introduce students to the fundamentals of astronomy concepts through readings in Black Studies. Texts may include works by theorists like Michelle Wright and Denise Ferreira da Silva, authors like Octavia Butler and Nalo Hopkinson, music by Sun Ra, Outkast and Janelle Monáe. Astronomy concepts will include the electromagnetic spectrum, stellar evolution, and general relativity.”

        https://classes.cornell.edu/browse/roster/SP21/class/COML/2034

        1. As per our host’s next post, maybe that holistic gobbledygook could be translated into Māori….?!

  4. Amazing confirmation (yet again) of Einstein’s singular brilliance and of the amazing things of which humans are capable when they collaborate in the name of science.

  5. I propose that SGR A* be renamed to “Donald”. It’s orange. It has a black heart. And, it devours everything in its orbit.

  6. “We have two completely different types of galaxies and two very different black hole masses, but close to the edge of these black holes they look amazingly similar.”
    Well, you know what they say. If you can’t see one black hole you can’t see them all.

  7. I don’t understand… isn’t the “hole” a sphere and the radiation is coming off in every direction? Why do we see a doughnut signature, I would have thought it would look like our sun, a ball of radiation (though a different spectrum, etc)?

    1. No, the radiation is not coming off in every direction. The gravity is so strong that the radiation is dragged inwards, it doesn’t get out, that’s the whole reason it is a “black hole”. What you are seeing is radiation from matter swirling around the black hole, that is in the process of falling into it. The cavity in the middle is where the black hole is.

      1. You misunderstand – the radiation from the swirling matter is what I’m talking about… this is three dimensions, is there some physics that makes the matter flatten out into a two dimensional disk before dropping into the black hole? I understand the vortex around a drain, but that’s basically two dimensions – the fact that we seem to have a “top view” of the swirling vortex seems very coincidental. If it’s a two dimensional matter disk falling into the black hole, then shouldn’t we see it edge on (at least a bit)? Hope I’m making myself clear…

        1. Yes there is something that breaks the three-dimensional symmetry, the spin of the black hole. It’s spinning, and the spin axis is pointing roughly towards us. So we’re largely looking down (plan view) on a two-dimensional disk.

          1. Thanks. It still seems improbably that both spin axes are pointed towards us, perhaps I’m not understanding the doughnut shape of the picture. The youtube suggestion on the other reply gives some effects for the reflected accretion disk which create the doughnut view even when edge on (when the spin axis is perpendicular to us).
            It would be interesting to me to see a model of the black hole with the resulting Earth image, and then rotate the spin axis in different directions and see how the image would change (or would it?).

            1. When the first black hole image was shown a couple of years ago, I remember seeing an explanation of why we see the bright spots where they are. I believe we are looking at a rotating disk of material spiraling into the black hole but it is distorted by the enormous gravity of the hole. Light that doesn’t go into the hole is still warped by gravity as it leaves the hole on its way to Earth. Here’s one, though I don’t know if it applies exactly to the new image:

              https://images.app.goo.gl/f2Ut8VPXYsnrNpTY7

      1. that was very helpful… am I to understand that no matter what angle the accretion disk is at we would see it as a halo around a dark center?

        1. Great question!
          I guess. My knowledge of black holes is … superficial.

          … that’s a scientific double entendre, I believe…

        1. I didn’t realize there is a new one – I meant the old first one : https://youtu.be/zUyH3XhpLTo

          … anyway, I’ll rewatch both but the first one has tangible models and the associated discussion was very impressive. As I recall, he goes “out there” later in the video using the computer.

        2. Ah – Mueller put the excellent discussion with his tangible model in the new video.

          Its so well done – so simple, but examines the consequences of those simple facts.

  8. I’d like to highlight what I find as perhaps the single most exhilarating thing about this black hole : not the scrupulous analysis and observation, although that is truly magnificent. It is not that we know a black hole exists.

    It is that the black hole has been there the whole time – right in front of our noses.

        1. Bah – I was in haste anyway – point is, the thing was there the whole time – that sort of idea. Discovery.

    1. And of course I know now, as I figured, SagA* was discovered not by this “photo” but a while ago.

      Still couldn’t resist highlighting the profound nature of discovery – of anything, really.

  9. Long time (decade-plus) physicist lurker here. I’ll be giving my take on the results in a live stream today/tomorrow. Hope to see some of you there!

    Our Black Hole! — Beyond the Image

    If the image is a sausage, how is it made? I will explain, at a non-technical level, why the Sgr A* results are at once incredibly exciting and rather sobering. Bring all your questions to this interactive live stream!

    https://youtu.be/BI3DYWjl9bo

    Friday, May 13, 8pm pacific

    1. I think the existence of the supermassive black hole at the Milky Way’s center has been known about for awhile now, but the picture is amazing! I think it’s assumed that most, if not all, galaxies have central black holes.

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