Four images from the paper. Over about a 2 hour period, Sgr A* flared to 75 times

Although the black hole in the middle of the Milky Way is a monster, it is still pretty quiet. Called Sagittarius A *, it is about 4.6 million times as massive as the sun. Usually it’s a brooding giant. But scientists observe Sgr. A * with the Keck Telescope was watching his brightness rise more than 75 times the normal for several hours. The flare is not visible in the optical light. Everything happens in the near infrared, the part of the infrared spectrum that is closest to the optical light. Astronomers have Sgr. A * for 20 years, and although the black hole has some variability in its performance, this blazing event is unlike anything astronomers have seen before. This peak was more than twice as bright as the previous peak flux. These results are reported in the Astrophysical Journal Letters in an article entitled “Unparalleled Variability of Sgr A * in NIR,” available at the arXiv.org prepress site. The lead author is Tuan Do, an astronomer at UCLA. The team saw Sgr. A * that flares 75 times normal for two hours on May 13th. At first, astronomer Tuan Do believed that they would see a star named SO-2 instead of Sgr. SO-2 belongs to a group of stars called S-stars that closely surround the black hole. Astronomers have kept an eye on how it circles the black hole. In an interview with ScienceAlert, Do said, “The black hole was so bright I first thought it was the star S0-2 because I had never seen Sgr A * so bright. In the next pictures, however, it was clear that the source was variable and had to be the black hole. I knew almost immediately that there was probably something interesting going on with the black hole. The question is, what sgr. A * torch like this? At this point, astronomers are not sure what caused the flare. A * has ever shown torches, just not so bright. The flaring itself is therefore not an isolated case.

A computer-simulated image of the hydrogen gas cloud G2 encountering Sgr. A*

It is likely that something disturbed the normally quiet neighborhood of the black hole, and there are at least a few possibilities. The first is not actually a glitch but an inaccuracy in the statistical models used to understand the black hole. If so, the model must be updated to include these variations as “normal” for Sgr. It is likely that something disturbed the normally quiet neighborhood of the black hole, and there are at least a few possibilities. The second possibility is where things get interesting: something has changed in the neighborhood of the black hole. The aforementioned star SO-2 is a major candidate. It is one of two stars that Sgr. A * in an elliptical orbit. Every 16 years it is the closest. Mid-2018 was his last approach, when it was only 17 light hours away from the black hole. The close approach of SO-2 may have disrupted the material flow in Sgr. That would produce the kind of variability and bright flare astronomers saw in May, about a year after the star’s approach. But astronomers are not sure. SO-2 is not a very big star, and it is unlikely that it could cause this kind of glitch. Not only that, it’s also the largest of the S-stars approaching Sgr. A *, so it is unlikely that any of the other stars could be the cause. Another possibility is a gas cloud. As early as 2002, astronomers saw what they considered to be a hydrogen-gas cloud approaching the center of Sgr. Not only that, it’s also the largest of the S-stars approaching Sgr. By 2012, the astronomers were sure that it was a cloud that was named G2. They measured the temperature of the cloud at 10,000 degrees Kelvin and were able to measure their trajectory: in 2013 it would move so close to the black hole that the tidal forces would tear it apart. At first, astronomers thought gas from G2 could be pulled into Sgr. A * s accretion disk, and that it would flicker brightly when heated. But that never happened. But it is still possible that his passage near the black hole triggered a chain of events that caused or contributed to the flare-up in May 2019. Ultimately, this flare-up (if there ever is one in science) can be the natural result of a variable material flow in Sgr. A *, which is likely to be lumpy. In this case, we will again update the statistical model that explains the variability of the black hole. The only way to know is to gather more data, not just with the keck, while the galactic center is still visible at night, but with other telescopes. In recent months, the galactic center has been visible, and riflescopes like Spitzer, Chandra, Swift and ALMA have been watching. These observations over several wavelengths should help clarify the situation if they are available.

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