December 2, 2022

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Tada: The first image of the black hole at the center of our galaxy |  National Geographic

Tada: The first image of the black hole at the center of our galaxy | National Geographic

It only took minutes after its announcement to see the enthusiastic reactions to the achievement from black hole researchers from around the world. “Beautiful shot of the ring around a black hole!!!!” UCLA astronomer Andrea Ges, the 2020 Nobel Prize winner in Physics, wrote about her research on Sagittarius A* in an email to National Geographic† “Bravo to the EHT Team.”

This second image of a black hole will help scientists further investigate whether contemporary physics (particularly Einstein’s general theory of relativity) also fits in the harsh environment surrounding a supermassive black hole. Moreover, by comparing this new observation with that of M87, researchers can learn more about the differences between black holes of different masses.

“During my PhD research, I thought a lot about this black hole,” says Cera Markov of the University of Amsterdam. “You are working on something very abstract and suddenly it is just there. You see the black hole with your own eyes.”

telescope extending over the earth

In April 2017, scientists targeted radio telescopes from eight observatories at the center of our galaxy. Telescopes, located in Hawaii, Spain and Antarctica, all observed arc A* when it appeared due to the rotation of the Earth. Once all these notes were entered, the team combined all the data using a technique known as Basal interferometry too long called to generate the image.

Capturing the image of Sagittarius A* was more difficult than capturing the image of the supermassive black hole of M87 observed during the same project. Sagittarius A* is located about 26,000 light-years away and may be the most massive object in our galaxy, but it is rather small for a supermassive black hole; The black hole has a mass of about 1/1500 at the center of M87.

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If the black hole weighing 6.5 billion suns descended at the center of M87 in our solar system, it would occupy about 130 times the distance between the Sun and Earth, while Sagittarius A* would not even orbit Mercury.

In addition, the view of Sagittarius A* is obscured by dust and gas swirling in the center of the Milky Way, making it difficult to combine observations into a single image. “Everything is moving faster around small black holes,” explains University of Arizona astrophysicist Demetrius Psaltis. “We were concerned that the plasma near the black hole would start moving in the eight hours that it would take Earth to spin enough to take a picture.”

In the end, it turns out that Sagittarius A* cooperates in the picture.

The hole in the center of the galaxy

The image shows some interesting details of the gravitational crater at the center of our galaxy, such as the direction of its rotation. This shows that the top of the black hole (or the bottom, depending on which way you look at it) is almost toward Earth. The mass of the hole was found to be in line with previous estimates made from the behavior of stars orbiting the black hole.

Surprisingly, the data also shows that this massive hole is not the so-called Jet It has an ultra-strong stream of particles being released into the universe. This phenomenon is relatively common in such objects, for example, the black hole of M87.

“There is now a discussion going on: Does Sagittarius A* have Jet And might it be difficult to realize this in such a complex environment because it is so small and vulnerable? “Based on our observations, our models predict the presence of an aircraft,” says Markov.

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When it comes to supermassive black holes, Sagittarius A* is the most fragile that the EHT can observe. Rather than devouring anything that got too close, the crater would go dormant, feeding on crumbs of stellar winds coming in from nearby stars, enough to form a visible ring. But there are indications that Sagittarius A* has been more active in the past.

We know that black holes go through cycles of activity. We can see that clearly when we look at supermassive black holes in galaxy clusters,” Markov said. “We can see the bubbles they make in nearby gas during their periods of activity. They seem to burst such bubbles every few hundred million years. So there is an on and off button.

The start and stop of the A* arc left traces on the particles in the interstellar medium, indicating (to some extent) varying degrees of activity over a time span of thousands of years, or even centuries. And while scientists know that the activity of a black hole varies with the amount of matter it swallows, it is still not known how this process works.

One way scientists are trying to learn more about the chaotic vortex around Sagittarius A* is to compare these processes with those around the Sun. The Sun is noticeably less massive, but bubbling bubbles, twisting magnetic fields, flames, explosions and superheated gas may help astronomers understand the physical laws of supermassive black holes.

“Of course, conditions are much harsher,” Markov says. “But surprisingly, a lot of our knowledge about the physics around the Sun also applies to black holes. We’ve already been able to apply some of the techniques.”

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In all shapes and sizes

Scientists hope that knowing the similarities and differences between M87 and Sagittarius A* will help them learn more about black holes in general. If some theories turn out to be true for things that vary a lot in size, then scientists can be confident that they are true for things that are less obvious.

“Verifying theories is very difficult in our field. We cannot fly into a black hole and see if what we think is really true. That is what we are trying to do now,” says Markov.

Black holes also allow physicists to test Albert Einstein’s 1916 general theory of relativity. The theory predicts, among other things, the existence of black holes. A phenomenon questioned by Einstein himself. But while the theory of quantum physics still raises questions, it appears to hold up so far even under extreme astrophysical conditions, while scientists wouldn’t be surprised if it didn’t.

“If you look at two things in the universe, one of which has a mass 1500 times less than the other, they usually cannot be compared. For example, think of a giant planet and a small asteroid, or a large and small galaxy, or an ant and an elephant, or a pebble and a mountain”, As Psaltis says.

“All theories on Earth apply to a certain scale, and if you change the scale, it will look different. Except for the general theory of relativity. This is the only theory where scale doesn’t matter. You can look at something very small, or you can look at something very large, and the behavior It’s exactly the same.”

This article was originally published in English at