How the first image of the supermassive black hole at the center of the Milky Way was captured

Milky Way black hole: There is now overwhelming evidence for the black hole, dubbed Sagittarius A*

Preston, UK:

Black holes are among the most profound predictions of Einstein’s theory of general relativity. Originally studied as a simple mathematical consequence of the theory rather than as physically relevant objects, they were soon seen as generic and sometimes inevitable results of the gravitational collapse that initially forms a galaxy.

In fact, most physicists suspect that our own galaxy orbits a supermassive black hole at its center. There are also other ideas, such as “dark matter” (an invisible substance thought to make up most of the matter in the universe). But now an international team of astronomers, including a team I led from the University of Central Lancashire, have unveiled the first image of the object lurking at the center of the Milky Way – and it’s a black hole. supermassive.

This means there is now overwhelming evidence for the black hole, dubbed Sagittarius A*. While it might seem a little scary to be so close to such a beast, it’s actually about 26,000 light-years away, which is reassuring. In fact, because the black hole is so far from Earth, it appears to us to be about the same size in the sky as a donut would be on the Moon. Sagittarius A* also seems rather inactive – they don’t devour much matter from their surroundings.

Our team was part of the global Event Horizon Telescope (EHT) collaboration, which used observations from a global network of eight radio telescopes on our planet – collectively forming a single virtual Earth-sized telescope – to take this stunning image. . The breakthrough follows the collaboration’s 2019 release of the first-ever image of a black hole, called M87*, at the center of the more distant Messier 87 galaxy.

Look in the darkness

The team observed Sagittarius A* for several nights, collecting data for several hours at a time, similar to using a long exposure time on a camera. Although we can’t see the black hole itself, because it’s completely dark, the glowing gas surrounding it reveals a telltale signature: a dark central region (called a “shadow”) surrounded by a bright structure ring-shaped. 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 discovery also gives valuable clues to the workings of black holes, which are believed to reside at the center of most galaxies.

Image from ALMA - one of the Event Horizon Telescopes.
ALMA – one of the Event Horizon telescopes.WikipediaCC BY-SA

The surprising thing about this image is that it looks so similar to the M87* image we posted three years ago – it sure came as a surprise. The reason for the similarity is that while the M87* black hole is about 1,000 times larger, the Sagittarius black hole is about 100 times closer. Both obey Einstein’s theory of general relativity, showing that Einstein was right by a factor of 1,000 in the size scale. For a physicist, this is important. Relativity has been around for a century and it still proves to be accurate. I think even Einstein himself might have been surprised by that!

The release of the Sagittarius A* black hole image is an extremely exciting achievement of the collaboration. When I first saw the image, I thought: this tells us a lot. I was eager to start writing about it and interpreting the image. We had many meetings to come to a consensus on what he is telling us. To begin with, we met face to face in different parts of the world. Then COVID hit and suddenly nobody could go anywhere. Online meetings have therefore become the norm, as in all other aspects of life. It definitely slowed us down.

My role was to help write two of the six articles that were published in Astrophysical Journal Letters: the first, presenting the observation; and the third, in which we discuss how we created an image from the observations and the reliability of this image.

In addition, I was a “contributing author” for all six articles. This is an administrative role, in which I handled all correspondence between our team of over 300 astronomers and the academic journal that published our findings. It came with challenges, as I had to deal with every typo and typesetting error.

I also had to channel comments from my colleagues. Since the majority of staff are based in the US or East Asia, this meant that they worked nights on UK time. As a result, every morning I would come into work to find around 100 emails overnight from co-workers – an intimidating start to the day.

Either way, we finally got there – and the dazzling result was worth all the work.The conversation

(Author: Derek Ward-Thompson, Professor of Astrophysics, University of Central Lancashire)

Disclosure Statement: Derek Ward-Thompson does not work for, consult, own stock or receive funding from any company or organization that would benefit from this article, and has not disclosed any relevant affiliations beyond his appointment. university.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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