EXPERT REACTION: First images of a black hole in our galaxy

Wow – that was incredible!  

The Event Horizon Telescope Collaboration have achieved a quite remarkable feat in imaging the supermassive black hole at the centre of our Milky Way galaxy. It was extremely impressive to see how they overcame the daunting technical challenges of imaging a rapidly-varying source, blurred by the effects of the gas lying along our line of sight to the black hole. Excitingly, the near-perfect agreement of the image with the theoretical predictions shows that Einstein's General Relativity has passed yet another stringent test, and the similarity of the image with that of M87 provides further confidence in our understanding of how a black hole looks and behaves. However, this is only a first glimpse into the black hole at the centre of our Milky Way; ongoing telescope upgrades should provide sharper images, and the next-generation facility being planned is aiming to provide real-time movies of black holes, allowing us to study the turbulent environment around these exotic objects. 

The image of the Milky Way black hole is not just "more of the same." The relative quietness of the Milky Way Black Hole relative to the M87 black hole can provide a significant advantage in advancing our understanding of black holes. M87, harbouring a very active black hole, with its enormous accretion and gigantic jets piercing through the galaxy at relativistic speeds has a lot more astrophysics happening in its vicinity. These astrophysical effects need to be carefully considered and separated in order to get to the heart of the black hole physics. Sgr A*, on the other hand, is much quieter in these aspects and can provide a much more pristine laboratory for explaining and advancing the physics of black holes.

Einstein's theory of general relativity has been way ahead of experiments for over a century. M87 and Sgr A* are only the beginning of a direct glimpse into black holes. That they agree with Einstein's theory is an amazing testament to the strength of the theory. With such experiments finally starting to catch up with theory, this is the advent of a new era of black hole physics!"  

It's amazing. The EHT literally could observe a doughnut on the Moon, and you'd see how big the hole is.

The EHT has provided yet another awe-inspiring visual confirmation of Einstein's theory of gravity and a testament to what humans can achieve when they work together.  Astronomy is truly at the dawn of a new era of big data, massive computer simulations, and high-resolution imaging.  

Very cool that they linked in the Antarctic station to create astronomy's highest-ever magnification image.

This evening, a remarkable image has grabbed the attention of the world’s media. Its resemblance to a humble cream doughnut belies the extraordinary technological achievement it represents. It shows the shadow of a black hole containing 4.1 million times the mass of the Sun at the very heart of our Milky Way Galaxy, clearly defined by a telescope the size of the Earth. Astonishingly, the predicted ring of radiation narrowly escaping the clutches of the black hole is visible at a magnification equivalent to what would be needed if the doughnut was located on the Moon.

For me personally, the image is a staggering illustration of how far astronomical science has come since I started my research career in the 1970s, because I, too, observed objects near the centre of our Milky Way Galaxy. They were stars, seen through the haze of dust between our Solar System and the galactic centre, and visible only as faint pinpoints of light. At the magnification of the EHT, they would look like discs of light with starspots visible on them! An amazing thought. 
 
Known as ‘Sagittarius A star’, the black hole in the image is some 27,000 light years from our Solar System. The successful observations were made in 2017 using the ‘Event Horizon Telescope’ (EHT), an array of eight high-frequency radio observatories spread around Earth’s western hemisphere. Each was equipped with special data recorders, atomic clocks and sensitive detectors. For the experiment to work, the weather had to be good at all the sites. But in the event, out of a 10-day allocation of telescope time, astronomers required only seven days.
 
The result was several petabytes of data – the equivalent of 5000 years’ worth of MP3 plays – which, over the past five years, have been reduced to an image of only a few kilobytes – but of enormous significance.

It’s an amazing image but perhaps more similar than I expected to the M87 one a few years ago?.

Astronomers have been talking about Sgr A* for over 20 years. It’s been really cool to see the movies of the stars whirling around it every few years, and the Nobel Prize, now we see this direct image, on a scale about 1000x smaller than those earlier images, of the supermassive black  holes event horizon itself. It’s a first and makes it real!  
The image is cool, very similar to the M87 one - which tells us I think that black holes are very similar even if they have greatly different masses, as we expect.  The image shows a central hole about the size of the orbit of Mercury (if I have done my math right while watching the press conference!), and the hole in the PR image is about twice the size of the expected event horizon. 

This was all quite a technical challenge, with the black hole spinning every few minutes, and hours long telescope observations, an amazing feat of algorithms and data processing. The telescope is effectively the size of the Earth, and I think this is one of the sharpest images ever made.

So I wonder why there are three spots in the accretion disk… 3 recent stellar casualties?

Sgr A* needs a better name!

It is extraordinary that the Event Horizon Telescope has captured the first image of the supermassive black hole at the heart of our very own galaxy (Sagittarius A*). Throughout human history, we have wondered what was at the centre of the Milky Way. Well, now we have an image of it.

The supermassive black hole conforms to the predictions of Einstein’s theory of general relativity. It’s remarkable how his theory, from just over a century ago, continues to stand up, despite our tests of it becoming more and more probing and exacting.
 
The image of the black hole bears remarkable similarity to the first image obtained by the EHT of the supermassive black hole in the galaxy M87, even though that black hole is about 1,000 times larger. This confirms a prediction of Einstein’s theory that black holes are basically all the same, perfectly symmetric, distinguished only by their mass and rate of spin.

The EHT image of Sagittarius A* is an amazing technological achievement and a great step forward from the M87 image of three years ago. Here we have one of the sharpest and most challenging images ever made, showing us the details of the black hole at the centre of our own galaxy. And once again it shows Einstein's predictions were spot on!

I’ve worked on supermassive black holes for my whole scientific career, and seeing with my own eyes the supermassive black hole at the centre of our own Milky Way has made me really emotional.

Historically we have only been able to see the light emitted from supermassive black holes as they consume matter as a point of light at the centre of external galaxies. The Event Horizon Telescope is revolutionary because it uses telescopes across the world as an Earth-sized telescope to resolve supermassive black holes in greater detail than has ever been possible. To produce this image of Sag A* they have not only done this, but also looked through all the stars, gas, and dust of our galaxy to the very centre where our own supermassive black hole resides.

These objects are the most energetic and mysterious objects in the Universe and I am so excited to see how much further they will continue to push our understanding of black holes in the future.

The first direct image of a ring of bright gas surrounding the ‘gentle giant’ black hole at the very centre of our Milky Way may at first sight appear underwhelming. After all, it doesn’t look that different from the ground-breaking image of the supermassive black hole in the galaxy Messier 87, dubbed M87*, that was obtained a number of years ago. Naively, one might perhaps have expected a sharper image of the centre of our galaxy given its much closer proximity. Yet, the M87* image is of a black hole that is some 1500 times more massive than the black hole in our Milky Way, which means that its ‘event horizon’ (traced by the bright gaseous ring) is also expected to be some 1500 times larger. Given that the M87* monster is about 2000 times more distant than the centre of the Milky Way, both images look remarkably similar.
 
But this second direct black hole image is much more than "more of the same"; it is not simply the result a repeat experiment. For one thing, it confirms that the M87* black hole appearance was not simply the result of data processing that led to a result the scientists wanted to see. We now have two laboratories in space that can be used to test Einstein’s remarkably robust theory of gravity—and which we have so far been unable to find at fault. The new image of Sagittarius A* in the centre of the Milky Way was much harder to obtain than that of M87*, most importantly because of the much more variable environment in which Sagittarius A* is located: given its much smaller size, orbital motions of the surrounding gas flows occur on much shorter timescales, and so it is no surprise that a large team of some 300 scientists with a wide variety of backgrounds and expertise was required to map this monster in our Milky Way.
 
Perhaps even more important than the actual scientific image just revealed, this achievement shows the power of and, indeed, the need for international collaboration in cutting-edge science, as well as the nature of modern astrophysics research. Astrophysics today is so much more than the study of stars and galaxies by individual scientists. Modern astrophysics pushes the boundaries of science and technology to their limits, in turn spawning new technological developments that themselves may lead to applications in a wide variety of practical fields in common use today. Whereas astrophysicists apply their craft to blue skies research, the spin-offs of their efforts have the real potential to benefit society in the form of advanced technological improvements and advances that eventually make life more comfortable and convenient

I'm blown away by this gorgeous image of the black hole Sagittarius A* - the centre of our Milky Way galaxy, discovered by the CSIRO in Sydney at the dawn of radio astronomy in the 1950s. For half a century astronomers have been zooming in closer finding stronger and stronger evidence that this object really is a black hole as predicted by Einstein, with Nobel Prizes along the way - but now we have definitive proof. 
 
These observations are an extraordinary tour de force technically. EHT's first-ever images of the black hole M87* a few years ago were extremely impressive, but Sagittarius A* is a moving target, and it required even more ingenuity in maths and software to develop today's time-lapse exposure of this flickering disk. This technology will be a milestone for years to come in taking high-resolution images with telescopes like James Webb and the Square Kilometre Array in Western Australia.

The results are extremely exciting indeed.  Wonderful images of the 4-million-solar-mass black hole at the centre of our Galaxy, showing a similar ring of light emitted by the hot gas spiralling into a black hole, with a shadow in the centre from the black hole itself.  General relativity passes again with flying colours (or orbiting colours? :) ).
 
One very interesting result is the very significant variability in the image. None of the models considered by the EHT fully explain this variability and some of the other features in the data. This is extremely interesting, and may point to further physics of magnetised accretion disks that we have yet to understand!

Today we got to see the first direct image of the supermassive black hole at the centre of our Galaxy. We have known for many years there was a large, compact object consistent with a supermassive black hole - in 2020, the Nobel Prize for physics was awarded to Andrea Ghez and Reinhard Genzel for the discovery of this compact object, though studying the orbits of stars around it.

Black holes are incredibly challenging to image - today we got to see a picture of the material swirling around what is most definitely a supermassive black hole at our Galaxy’s centre, thanks to the work of the Event Horizon Telescope team. Eight years ago, I was an honours student, studying how the curvature of spacetime caused by the incredible mass of the supermassive black hole affects the orbits of objects close to it. It’s thrilling to see the supermassive black hole itself, I feel like I’ve finally got to meet an old friend. The discovery is a testament to the power of international collaboration, and will be a source of inspiration for scientists all over the world.