Earth’s Astronomers on the Significance of the First Image of Milky Way’s Supermassive Black Hole

Image of Sagittarius A* (Sgr A*)

 

Several of the world’s leading astronomers and scientists emailed their thoughts to The Daily Galaxy on the significance of the fist image by the Event Horizon Collaboration of our Galaxy’s supermassive black hole. Their comments validate Albert Einstein’s observation that “the scientific imagination is a preview of coming attractions.”

Niayesh Afshordi, astrophysicist with in the Cosmology and Gravitation group at the Perimeter Institute for Theoretical Physics (PI)

“The recent EHT radio image of the supermassive black hole at the center of the Milky Way is a culmination of amazing feats of technology, imagination, and science. In particular, it provides us with a direct window into the most twisted geometries that, to our knowledge, nature has ever cooked up. Most spectacularly, the size of the hole exactly matches the century-old solution of the German  physicist, Karl Schwarzschild, for the mass measured on scales that are over three orders of magnitude bigger, from motion of stars.” 

It provides us with a direct window into the most twisted geometries that, to our knowledge, nature has ever cooked up.”

James Binney FRS Emeritus Professor of Physics, Oxford University

“It’s quite a surprise that the image is so nearly circular, suggesting that the black hole’s spin axis points quite far from the Galaxy’s spin axis.”

Paul Davies, Regents’ Professor at Arizona State University and Director of the Beyond Center for Fundamental Concepts in Science, author of What’s eating the Universe.

“When Sagittarius A* was first identified as a black hole – admittedly massive, but oh so tiny in size – it never occurred to me that anyone would obtain an actual image of it in my lifetime. But I was wrong. What an incredible technical accomplishment!”

Eric Gawiser, Professor of Physics and Astronomy, Rutgers University

“The most significant scientific advances change how we view the world we live in. We have just experienced such a moment, with the publication of the image of the Supermassive Black Hole at the center of the Milky Way by the Event Horizon Telescope collaboration.  The Sun and all of its planets, including our beloved home on Earth, orbit the center of our galaxy once every 200 million years.  We already had solid evidence that there was a huge black hole right at the center of our galaxy, but now we’ve seen it.  I’ve never before viewed a photo of our universe that was so simultaneously beautiful and terrifying..” 

I’ve never before viewed a photo of our universe that was so simultaneously beautiful and terrifying.”

David J. Helfand, Professor of Astronomy, Columbia University; Chair, American Institute of Physics, Legacy Fellow and Past President, American Astronomical Society

“The image of Sagittarius A* by the EHT is a tour de force of image processing and provides a tantalizing hint of what we could learn with an array of telescopes that allowed us to make a movie of black holes having lunch.”

Daniel Holz,  Professor at the University of Chicago, in the Enrico Fermi Institute, the Department of Physics, the Department of Astronomy and Astrophysics, and the Kavli Institute for Cosmological Physics.

“It is wonderful to finally see the supermassive black hole at the center of our very own Milky Way. Although, of course, we don’t ever see a black hole, since it emits no light (or anything else, for that matter). Instead, we get to see the stuff falling in, and that teaches us how black holes eat and grow to such enormous sizes!”

It’s like knowing that a 100,000 pound dragon lives in your backyard, but never managing to get a glimpse of it.”

Dan Hooper, University of Chicago cosmologist and particle physicist specializing in the areas of dark matter, cosmic rays, and neutrino astrophysics. Author of At the Edge of Time.

“For years, we’ve known that an enormous black hole resides at the center of our galaxy, but until now we’ve never been able to see it. It’s like knowing that a 100,000 pound dragon lives in your backyard, but never managing to get a glimpse of it.”

Avi Loeb, is the Frank B. Baird, Jr., Professor of Science at Harvard University and a bestselling author. He received a PhD in Physics from the Hebrew University of Jerusalem in Israel at age 24 (1980-1986), led the first international project supported by the Strategic Defense Initiative (1983-1988), and was subsequently a long-term member of the Institute for Advanced Study at Princeton (1988-1993). Loeb has written 8 books, including most recently, Extraterrestrial (Houghton Mifflin Harcourt, 2021), and nearly a thousand papers (with an h-index of 118) on a wide range of topics, including black holes, the first stars, the search for extraterrestrial life and the future of the Universe.

“It is wonderful to see the face of Sagittarius A*. Now we can post it as a tourist destination, where you could see your back by looking forward at the photo n ring, or where time is ticking more slowly and you can outlive your relatives on Earth by staying near the black hole horizon, and where the spectacle of the entire universe reflected and distorted as gravitationally lensed images around the black hole. Tickets at discounted prices should be offered to string theorists who would like to test their ideas close to the singularity. These tickets will obviously be only one way.”

Now we can post it as a tourist destination, where the spectacle of the entire universe is reflected and distorted as gravitationally lensed images.”

Maxwell Moe, astrophysicist, NASA Einstein Fellow, University of Arizona

“It is absolutely amazing to see the differences between the supermassive black hole in M87 imaged by the EHT a few years ago and their recent image of our own Galaxy’s central black hole, which is 1,000 times smaller and less massive. We can now directly see the variations in the geometry and timescales of the accreting material, providing empirical tests of accretion disks, general relativity, and black hole physics on different mass scales.”

Mark Morris, UCLA, Galactic Center Group — has been studying the innermost regions of our Milky Way Galaxy for over 40 years. Professor Morris co-discovered the magnetic filaments that pervade this Galactic region, which led to a new area of research within astronomy. He is also the co-discoverer of the ‘Double Helix’ Nebula , as well as the bipolar X-ray lobes that appear to have resulted from mass outflows near the central black hole.

“The long-awaited and spectacular image of what we should now call the Galactic Black Hole (GBH) is a marvelous coup, inasmuch as the Event Horizon Telescope team had to overcome a serious challenge that they did not have to face to produce their previous image of the black hole in M87. That challenge was the variability of the emission from the GBH.  It fluctuates on time scales as short as 5 to 10 minutes, so the long exposures needed to capture a clear picture of the instantaneous profile of the glowing gas accreting onto the hole were not possible, and the team had to develop a way to combine a large number of snapshots to produce a time-averaged image.  

“The next step will be to go beyond a static image, and to develop a way to show a dynamic sequence of images so that we can watch the glowing gas as it orbits the GBH, as it spiral inward in its orbit,  or as some of it is energetically expelled as a result of all the energy being generated in the accretion process. That step will require advances in telescope sensitivity, more telescopes, or  the development of new techniques to overcome the noise threshold and thereby to capture and  follow the emission from any hotspots that may be present.  Another way to move forward would be for the EHT team to serendipitously capture a particularly bright flare, which happens on rare occasions (our group at UCLA observed one in 2019).   Such an event might make it possible to get a relatively rapid sequence of clear images.  

“In any case, the EHT team has more data than they have presented so far, so I very much look forward to their future analyses and presentations.”

Christopher Stubbs, Professor of Physics & of Astronomy, Dean of Sciences, Harvard University

“It’s a milestone to have an image of the dark heart of the Milky Way!”

Meg Urry,  the Israel Munson Professor of Physics and Astronomy, and Director of the Yale Center for Astronomy and Astrophysics.

“There are many things to say about this beautiful work but perhaps the most impressive part of the result is that the Sagittarius A* black hole, which is about 1000 times smaller than the M87 black hole reported three years ago, casts exactly the same kind of shadow, only about 1000 times smaller in absolute size. (They have similar angular sizes on the sky, since M87 is much farther away, which is why EHT can resolve the event horizons of both.) Einstein predicted that the properties of black holes would scale with mass in precisely this way.

“One other interesting aspect of this new result: because the Sgr A* black hole is much smaller, its appearance was changing during the observations. (The time scale for variability in M87 is 1000 times larger, so it was essentially constant while it was observed with EHT.) This made the work of figuring out the exact shape of the image much more difficult, so that makes this particular image a particular triumph.”

Dan Wilkins, Kavli Institute for Particle Astrophysics & Cosmology at Stanford University

“With the new EHT results, we have an actual image of the supermassive black hole in the center of our own Galaxy. Up until now, we’ve inferred the presence of the black hole by a range of indirect measurements, such as the motion of the stars, which requires there to be a massive, compact object in the centre, but we rely on the theory of General Relativity to tell us that something so massive and so small must be a black hole. We are now able to see the the shadow of that black hole, from which no light can escape. As our nearest supermassive black hole, we’ll be able to use measurements of Sgr A* to really test our understanding of gravity, and understand the role it played in the growth and development of the Galaxy as we see it today.

“It’s always fun when we have new observations and as well as giving us answers, they pose interesting new questions, One thing that strikes me about the new image is that it appears that we are looking at the disk of gas around the black hole face-on. We are living on one of the outer turns of the Milky Way spiral galaxy, so we’d expect to be looking at the disk of gas edge-on if it was aligned with the Galaxy, but it looks like it’s not, so watch this space!”

We are living on one of the outer turns of the Milky Way spiral galaxy, so we’d expect to be looking at the disk of gas edge-on if it was aligned with the Galaxy, but it looks like it’s not.”

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