Astronomers reveal the first photograph of a monster black hole at the heart of our galaxy


More than 27,000 light-years away, at the heart of our galaxy, lies a supermassive black hole, which is more than four million times the mass of our sun. He has never been seen.

Till today.

Astronomers using the Event Horizon Telescope (EHT) have taken the first image of the Milky Way’s supermassive black hole, named Sagittarius A*.

Astronomers have long speculated about a black hole at the center of our galaxy. Observations of stars near the core showed them orbiting something invisible, suggesting a black hole. Today’s image post is a confirmation.

The results were published today in a special issue of Astrophysical Journal Letters.

Black holes are relatively small, invisible, and extremely dense regions of space with a gravitational field where anything that crosses their threshold – known as the event horizon – is drawn in, never to return. This includes light, which is why they’re so notoriously difficult to detect unless they’re interacting with a nearby star.

However, in 2019, the EHT – an organization of over 200 astronomers from around the world, including Canada – published a historic first photograph of a black hole at the center of another galaxyMessier 87 (M87), which showed the shadow of the black hole with its surrounding gas illuminated.

Size comparison of the two black holes imaged by the Event Horizon Telescope (EHT) collaboration: M87*, at the heart of the Messier 87 galaxy, and Sagittarius A* (Sgr A*), at the center of the Milky Way. The image shows the scale of Sgr A* relative to both M87* and other solar system elements such as the orbits of Pluto and Mercury. (EHT Collaboration)

Like M87, the newly released image shows the hot material surrounding the shadow of Sagittarius A* (pronounced Sagittarius A-star).

The image was taken using eight radio telescopes in six locations around the world: Chile, Mexico, Spain, Hawaii, Arizona and even the South Pole. Used together, they act like a giant Earth-sized telescope capable of obtaining much more detailed images. Data for M87 and Sagittarius A* were collected in 2017.

More than pretty pictures, the data collected can shed light not only on the formation of supermassive black holes but also the role they played in the early universe and the role they continue to play at the heart of galaxies, most of which are home to these puzzling structures.

In any case, this is the hope of astronomers and astrophysicists around the world.

Ue-Li Pen, an astrophysicist and collaborating scientist with the Event Horizon Telescope project, compared these new images and the data collected to the difference between reconstructing a dinosaur from what we understand and actually seeing one.

“I think the dinosaur analogy isn’t that different,” said Pen, who is also a professor at the Canadian Institute for Theoretical Astrophysics at the University of Toronto. “[It’s] a bit like seeing a living dinosaur in your neighbor’s garden: we can’t touch it yet. But it’s so much closer and so much newer – and so much more alive than anything that came before it.”

The challenges of obtaining these images

Creating images of the two black holes presented different challenges. In the case of M87, its black hole is one of the most massive known. It is six billion times more massive than our sun and 1,500 times more massive than Sagittarius A*. It is also 2,000 times further away than Sagittarius A*.

Along with Sagittarius A*, although closer, it lies along the galactic plane, meaning telescopes must peer through thick gas, dust and plasma. Additionally, its black hole is smaller, measuring 4.3 million times the mass of the sun.

This is the first ever image of the event horizon of a supermassive black hole, captured by the Event Horizon Telescope in 2017. (Event Horizon Telescope)

“For Sagittarius A*, it’s…almost 2,000 times smaller [than M87], and that means light gets around it in 2,000 times less time,” said Avery Broderick, associate professor at the University of Waterloo, associate faculty member at Perimeter Institute and member of the EHT team. “It’s about 15 minutes. So, every 15 minutes a day, he begins to show us a new face.”

He compares looking through all the plasma, dust and gas to looking through an ice-covered window.

“That’s pretty much what radio astronomy looks like across the galactic plane – galaxy wrecks and jetsams play the role of ice and blur and alter images,” he said.

“So to fix that, we can play games to remove the blur. But addressing how to deal with the kind of ripple effect that you see, that was one of the things we had to figure out how do so effectively, so we could produce an image that showed what the source looked like.”

“Unlike Everything Else”

Black holes have a fascinating history. They were first predicted by theoretical physicist Albert Einstein in his theory of general relativity in 1915. Even though his own calculations predicted them, Einstein did not believe that nature could crush something with the mass of a star in such a compact space. However, the astronomer and physicist Karl Schwarzschild, who fought in the trenches on the German front during the First World War, managed to prove that they could indeed exist.

This new image is therefore another testament to Einstein’s theory of general relativity, Broderick said.

This illustration shows how astronomers are able to photograph black holes. (ESO)

“The fact that the shadows are the right size, I think, is incredible confirmation that Einstein’s theory of gravity, Einstein’s general relativity, is still at 1,000,” he said. “He always answers every question put to him with precision, which sometimes is frustrating because we are always looking for something, something new and different.”

Janna Levin, who did not participate in the EHT announcement, is a renowned astronomer who has made it her mission to learn as much as possible about black holes.

This 2018 time-lapse video from ESO’s Very Large Telescope in Chile shows stars orbiting the supermassive black hole that sits at the heart of the Milky Way over a period of nearly 20 years. (European Southern Observatory)

“Stars can be different in many ways. Black holes can’t. Black holes are almost like a fundamental particle the same way an electron is like a fundamental particle,” said physics professor Levin. and astronomy at Barnard College of Columbia University in New York and author of black hole survival guide.

“If I have a black hole that has a certain charge, an electrical charge, like static electricity and a certain mass, and it spins a certain way, it’s absolutely indistinguishable from any other hole. With those three numbers – three numbers, that’s it – you couldn’t tell if this black hole was made of antimatter, dark matter, encyclopedias, ghosts, stars, photons.

“They don’t reveal anything about themselves.”

Our fascination with black holes

Whether we have seen them or not, black holes have long captured the public imagination. In 1979, Disney made what is now considered a notoriously bad movie called The black hole. And these gravitational monsters have continued to appear in movies, most recently the 2014 drama Interstellar.

It was through this film that we got our first real idea of ​​what a black hole might look like. Nobel Prize-winning astrophysicist Kip Thorne performed calculations on a supercomputer to try to present a realistic view of what a black hole might look like. The result was the shadow of a black hole with light curving around it due to its massive gravity, called gravitational lensing. When the image of M87 was released, it matched this almost perfectly.

Broderick and Pen both believe that a better understanding of black holes will in turn help us better understand gravity as a whole.

“Why is this important in a larger sense? Well, I’m getting a little philosophical on this,” Broderick said. “We live in this information age now, I’m talking to you, on Zoom, and my computer is on Wi-Fi, communicating with another computer that’s beamed to you around the world. And it all works because of the equations of Maxwell, James Clerk Maxwell wrote a description of electromagnetism.

“I don’t know any more than Maxwell could have predicted cell phones, which the age of gravity will provide. We could all fly in Jetson-like cars because of it, or you could warp through the ‘universe.”