Astronomer Sarah Esson contributed a picture of our black hole. From the deserts of Arizona looking for other black holes. “I hope we can capture another unique moment.”
Last week, an image of Sagittarius A*, the Milky Way’s black hole, was presented. This has been the goal that Event Horizon Telescope scientists have been working on since its inception. Sarah Issa, one of the participating scientists, talks about what this discovery means to science, how she experienced the lead up to the press conference and what we can expect in the future.
Esson is an astronomer at the prestigious Harvard University Center for Astrophysics. Since 2014, it has been part of the Event Horizon Telescope (EHT) collaboration, the massive project that has connected eight telescopes from the deserts of South America to the South Pole for the A* Sagittarius image. This is black matter at the center of our galaxy, which until the photo was taken was only suspected to be a black hole.
In 2019, the group of scientists already made headlines with an image of the M87 black hole. Last week, this was followed by an image of Sagittarius A*, our own black hole.
Last Thursday it’s time. More than fifteen years later, the EHT question has been answered. The dark matter around which our Milky Way orbits is actually a black hole, and it’s visible on the screen. “It was very exciting,” Esson says excitedly. As a research group, we weren’t allowed to say anything about it until we were really looking forward to that day. Then the moment finally came.
Many people probably remember M87, the first image of a black hole. Therefore, this discovery may seem to the general public just a “second picture”. How is this for you?
I fully understand that this finding may be less interesting to the general public. The last time, of course, something “tangible” was introduced for the first time. This modernity has now vanished. From a scientific point of view, this is a big step. We’ve seen for some time that the stars in our galaxy orbit something strange, something that should be in the middle of our galaxy. We didn’t know at the time that this was a black hole, even though it looked like it.
How do you know for sure that it is a black hole?
By looking at how stars move around this heavy matter, we were able to determine its gravity and weight. In black holes, mass and volume are related: if you know the mass of a black hole, you can also calculate its volume. According to Einstein’s general theory of relativity, you can then determine how big a shadow a black hole should leave behind, when you take a picture of it – as we’ve done now. When we got the picture, the shadow appeared to exactly match our predictive calculations. Then we were able to determine that it is indeed a black hole.
what do you see?
The black hole itself cannot be captured. Every particle of light diving on it is absorbed by the colossal gravity. Thus, the orange border on the known images is not light rays, but particles of radio radiation that have just managed to escape. EHT telescopes can collect this radiation. The researchers then digitally combine the signals and convert them into a “normal” image.
Picture of Sagittarius A*, the black hole that is the center of our galaxy. Photo: EHT
What does this assertion mean to science?
We think that the center of almost all galaxies is made up of a supermassive black hole, just like our own. We don’t know exactly how they got there, but almost every galaxy seems to have one, around which everything revolves. This is special. Despite their enormous size, these black holes are relatively small compared to galaxies. However, they possess tremendous power. They send out plasma rays, “eat” the matter and shoot it back – sometimes even to other galaxies. All of these processes occur at nearly the speed of light. So they are the most powerful energies in the universe.
Black holes are also responsible for the formation of stars and planets. Our life may also have arisen from our own black hole ‘eruption’. But it can also collide with other galaxies. Then the holes merge to form a supermassive black hole.
This is the fate of our Milky Way galaxy. Although it will take some time, only after sunset. By looking at our own black hole and comparing it to one like M87, researchers hope to understand black holes much better in the future.
We’re also a lot further along in confirming Einstein’s theory of gravity. There are a number of other theories about gravity that we can’t all rule out at this point. So we can’t yet confirm Einstein’s theory with certainty, but we’re on our way.
Filming the M87 was a gamble.
Hino Falk noted that for him this discovery was a closure. Wedding after the first kiss. It sounds like you’re basically looking to the future.
I understand Hino Falk. He’s been working on this for 25 years. The story of shooting the A* bow is also closely related to the story of EHT. This is the reason for this collaboration at all. In fact, I see black hole imaging as the beginning of something new.
Filming the M87 was a gamble. We didn’t know the size of the black hole, so there was a good chance we wouldn’t be able to see it with our technology. The bow A* was the hole we’d been chasing all along. Now that we know how to do it, we can explore more from there. I see it as if we’ve been working all the time building some kind of ‘lab’, a method. Now that that’s done, we can do so much more.
“Unfortunately, the data we collected in 2017 on M87 and Sagittarius A* isn’t good enough to know how black holes change over time. We need more data for that, which is what we’re working on. We’ve now been able to connect eleven Telescopes. In 2017, there were still eight. The data we can collect increases exponentially with each addition of a telescope, so these three add up a lot.
“Maybe we’ll see a black hole explode”
We can now use it to take new measurements and make videos. This way we can see how black holes change over time and hopefully understand them better. We might see a black hole explode. Or we can capture another unique moment. It’s like opening a new lab: you see all kinds of stuff, you pick some and try it, but there’s a lot you haven’t touched yet. I’m really looking forward to discovering all of that.
The EHT regularly confirms that these findings are the result of a group project. However, more often than not, studies highlight some key characters. What’s wrong with that?
‘This is correct. Therefore the first author of our article is “EHT Collaboration”. The authors are then listed in alphabetical order. This has several reasons. First, with a project as large as this, it is impossible to say who made the biggest contribution. In addition, you cannot do this project on your own. You need a lot of people from many different disciplines. From people with extensive knowledge of the material to the people who do the physical calculations and the people on the site.
I don’t think this applies only to this project. You are not working alone in science. The amount of work that precedes the new results cannot be accomplished by a single person. I think that is why it is so important to demonstrate this global cooperation. That we’ve been able to achieve this together, through language barriers, cultural differences and even the pandemic. It’s amazing how people from completely different backgrounds come together when you’re working toward a common goal.
The role of Radboud University
Radboud University plays a major role in research into black holes. For example, the university has allocated a lot of money to research and astronomy Professor Hino Valcke is one of the big names in this field. The “Heino Falcke Group” consists of several PhD students, including Sarah Issa.
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