See the first image of the black hole in the center of our galaxy

Within minutes of announcing the discovery, black hole researchers around the world hailed this remarkable achievement. “It’s a great picture of the ring around the black hole!!!” National Geographic Andrea Ges, an astronomer at the University of California, Los Angeles, is the recipient of the 2020 Nobel Prize in Physics for her study of Sagittarius A*. “Bravo to the EHT team.”

With an image of another black hole in hand, scientists can continue to study whether physics as we know it — and in particular, Einstein’s theory of relativity — holds up in the harsh environment around a supermassive black hole. By comparing these new observations with those of M87, researchers can learn more about the behavior of black holes of different masses.

“I thought a lot about this black hole during my PhD,” says Sera Markov of the University of Amsterdam. “Sometimes we are working on something very abstract, but all of a sudden there is. And we are looking at a black hole.”

world size telescope

In April 2017, scientists pointed the radio telescopes of eight observatories toward the heart of our galaxy. Scattered from Hawaii to Spain to the South Pole, telescopes spotted Sagittarius A* as viewed by the Earth’s rotation. After collecting the observations, the team combined data from each telescope — using a technique called very long fundamental interferometry — and used the data to work on creating the image.

Creating the image of Sagittarius A* was not as straightforward as it was in the case of the supermassive black hole of M87, which was observed during the same research expedition. About 26,000 light-years away, the Sagittarius A* black hole may be the most massive thing in the galaxy, but it’s very small as far as supermassive black holes go – its mass is about 1/1500 the mass of the central black hole. Messier 87.

If the M87 black hole, which contains 6.5 billion solar masses, were located at the center of the solar system, it would destroy everything up to 130 times the distance from the Earth to the Sun; However, Sagittarius A* will not fill Mercury’s orbit.

Sagittarius A* is heavily obscured by dust and gas at the center of the Milky Way, and the environment there is incredibly variable — vortex, turbulent, smoldering — making it difficult to combine all the observations into one image. “Things around smaller black holes are moving faster,” says Demetrius Psaltis, an astrophysicist at the University of Arizona. “We were concerned that the plasma around the black hole wouldn’t stay stationary for the eight hours it would take for Earth to rotate for us to take a picture.”

However, Sagittarius A* eventually collaborated in creating her image.

The abyss at the center of the galaxy

This new image reveals some key details about the gravitational drain at the center of our galaxy, including the direction of its rotation, which indicates that the top of the black hole — or the bottom, depending on your perspective — faces almost directly toward Earth. Its mass also appears consistent with estimates made earlier from the study of stars orbiting the black hole.

But there is one detail that is somewhat troubling – the data also shows that this supermassive black hole does not appear to be releasing a powerful jet of particles into the universe, a relatively common feature of such objects, including the black hole in M87.

“So the debate now is whether Sagittarius A* is actually launching an aircraft, and whether it is difficult to monitor because of its complex environment and being so small and vulnerable,” says Sera Markoff. “Taking into account everything we’re watching, our models predict that there must be an aircraft.”

As far as supermassive black holes go, Sagittarius A* is the “least powerful” object the EHT has been able to spot so far. Instead of devouring anything that gets too close to the black hole, the black hole is dormant, content with the remnants of stellar winds fired by nearby stars and feeding on enough crumbs to form a visible ring. There is still plenty of evidence to suggest that Arch A* was more active in the past.

We know that black holes go through cycles of activity. We see this clearly when we look at supermassive black holes in clusters of galaxies,” says Serra Markov. “We can see bubbles spewing out during their active cycles in the surrounding gas, and it appears that these bubbles burst every hundred million years or so. So it looks like there’s an on and off switch.”

The activity of the Sagittarius A* black hole has left marks on particles in the interstellar medium indicating that its activity varies – at least moderately – on time scales of millennia, or even centuries. And while scientists know that a black hole’s activity varies depending on how much material it takes in, it’s unclear exactly how this process works.

One way scientists are trying to understand this chaotic storm surrounding Sagittarius A* is by comparing it to the Sun. The Sun’s mass is much smaller, but sparkling perturbations, twisting magnetic fields, eruptions, eruptions and billowing gas could help astronomers learn more about the physics around supermassive black holes.

“This is clearly a more extreme regime,” says Sera Markov. “But what I find amazing is that a lot of what we’ve learned from solar physics can be applied to black holes in many ways — in fact, we’ve borrowed some of the technology.”

All sizes and shapes

Scientists now hope that a deeper understanding of M87 and Sagittarius A* black holes – including their similarities and differences – will help them better understand the broader group of black holes. If theories are valid for things of varying sizes, scientists can be more confident that their theories accurately explain things that cannot be clearly observed.

“In our field, the verification process is really very difficult. We usually can’t fly into a black hole and see what happens. But that’s what we were able to do in this case,” says Sera Markov.

Both black holes allow physicists to test Albert Einstein’s theory of relativity in 1916. Black holes are one of the theory’s predictions – an outcome that Einstein himself was skeptical of. However, despite some mysteries in the quantum world, it seems that general relativity still holds, even in extreme astrophysical environments, where scientists expect it to fail.

“If we take two things in the universe that have a mass difference of 1,500 times, then those two things will not look alike – we can use a giant planet and a small asteroid as an example, a huge galaxy and a small galaxy, an ant and an elephant, a rock and a mountain,” says Demetrius Psaltis.

“All theories in the world have a scale, and when we move from one scale to another they look different. Except for general relativity. It is the only theory that has no scale. We can look at smaller and larger, and they behave in exactly the same way.”

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