Black holes are among the most profound predictions of Einstein’s theory of general relativity. Originally studied as a mere mathematical consequence of theory rather than 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 have suspected that our own galaxy revolves around a supermassive black hole at its center. There are other ideas as well, 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, has revealed the first image of the object lurking at the center of the Milky Way, and it is a supermassive black hole.
This means that there is now overwhelming evidence for the black hole, dubbed Sagittarius A*. While it might seem a bit scary to be this close to such a beast, it’s actually about 26,000 light-years away, which is reassuringly far. 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 on the Moon. Sagittarius A* also seems quite inactive: it is not devouring much matter from its environment.
Our team was part of the global Event Horizon Telescope (EHT) Collaboration, which has used observations from a global network of eight radio telescopes on our planet, collectively forming a single virtual Earth-sized telescope, to take the stunning image. The breakthrough follows the collaboration’s 2019 release of the first image of a black hole, called M87*, at the center of the more distant Messier 87 galaxy.
looking in the dark
The team observed Sagittarius A* over several nights, collecting data for many 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 ring-like structure. The new view captures light deflected by the powerful gravity of the black hole, which is four million times more massive than our Sun. The discovery also sheds valuable clues about the workings of black holes, which are thought to reside at the center of Earth. most galaxies.
The amazing thing about this image is that it looks so much like the M87* image we published three years ago; this was certainly a surprise. The reason for the similarity is that while the black hole M87* 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 1000 on the size scale. For a physicist this is important. Relativity has been around for a century and is still proving to be accurate. I think even Einstein himself might have been surprised by that!
The release of the Sagittarius A* black hole image is a tremendously exciting achievement of the collaboration. When I first saw the image, I thought: this tells us a lot. I couldn’t wait to start writing about it and interpreting the image. We had many meetings to reach a consensus of what he tells us. To begin with, we were meeting face to face in different parts of the world. Then COVID hit and suddenly no one could go anywhere. So online meetings became the norm, as in all other aspects of life. This definitely slowed us down.
My role was to help write two of the six articles that have been published in the Astrophysical Journal Letters: the first, presenting the observation; and the third, in which we discuss how we made an image from the observations and how reliable that image is.
In addition, I was a “contributing author” on all six articles. This is an administrative role, in which I handled all correspondence between our team of more than 300 astronomers and the academic journal that published our findings. This had its challenges, as I had to deal with every typo and typo error.
I also had to channel feedback from my peers. Since most contributors are based in the US or East Asia, it meant they were working overnight on UK time. Therefore, each morning I would arrive at work to find around 100 overnight emails from colleagues, a discouraging start to any day.
Anyway, we got it in the end, and the stunning result was worth all the work.
This article by Derek Ward-Thompson, Professor of Astrophysics at the University of Central Lancashire, is republished from The Conversation under a Creative Commons license. Read the original article.