The supermassive black hole on the prowl at the center of the Milky Way is aware of powerful outbursts, and new evidence shows that it is surrounded by a strange speck that flies through space at 30 percent of the speed of light.
Thanks to the innovative Event Horizon Telescope (EHT), astronomers can peer deeper into the 4 million solar mass black hole at the core of our galaxy called Sagittarius A* (Sgr A*). The latest look at this compelling scientific target was published Thursday in the journal astronomy and astrophysics, and has revealed a fast-flight hotspot as well as new information about the mysterious flares shooting around the black hole. The phenomena help scientists learn more about the behind-the-scenes chaos of the black hole, and they’re also fascinating in their own right.
Here’s something to ponder: The disk of gas surrounding Sgr A* appears in the sky comparable in size to an orange on the Moon’s surface as seen from Earth. Now imagine a grapefruit twice the size of the orange and you will get the approximate orbital size of this bubble. That’s just apparent size; models suggest the bubble has an orbital radius similar to that of Mercury around the Sun. To put the droplet’s speed into perspective, imagine Mercury making a trip around the Sun in a whopping 70 minutes instead of its typical trip of 3 months.
What they found – “Which comes first, a bubble or a flare, could be a kind of chicken-or-egg question,” says Maciek Wielgus, an astrophysicist at the Max Planck Institute for Radio Astronomy in Germany who led the new work. Reverse. Wielgus was part of the EHT team that produced the fascinating first image of Sgr A* in May 2022.
“Our results seem to indicate that it is the flare that appears first and, through this powerful release of energy from the magnetic field in the plasma, creates hot spots or bubbles,” he adds. Plasma is a state of matter produced when powerful forces further heat material.
Solar flares, like the ones that now appear more frequently when the Sun wakes up in the most active part of its 11-year cycle, resemble the explosions produced by the supermassive black hole. “The mechanism through which we believe that the [black hole] a flare occurs is magnetic reconnection,” says Wielgus. “And fundamentally, it’s similar to the origin of flares on the Sun’s surface.”
“However, there is a big difference in geometry, plasma properties and the overall power involved,” he adds. That said, just because Sgr A* far outclasses the Sun doesn’t mean it’s a titan among its peers.
“While Sgr A* is as massive as about 4 million Suns,” says Wielgus, “it only emits with a power of about 100 Suns, which is actually very unimpressive for a supermassive black hole!”
That Sgr A* is weak by black hole standards might invite a sigh of relief. It is, after all, in our cosmic backyard. It’s 27,000 light-years away, but still a stone’s throw away by Universe standards.
This tame supermassive black hole is, however, capable of volatile activity. And the new study helps clarify why these outbreaks and the bubble occur.
Why does it matter? Co-author Monika Mościbrodzka, who works at Radboud University in the Netherlands, says in a Thursday announcement from the European Southern Observatory (ESO) that they now have “strong evidence” that these eruptions originate from magnetic interactions when the orbits of very hot gas close. to Sgr A*.
Their explanation for these flares and hot spots is that, when a black hole’s magnetic field line reconnects (as they do on the Sun’s surface), the event releases a lot of energy very quickly. This hits some of the gas around the black hole, heating it up and forming what Wielgus describes as a “plasma bubble with a low density and a very high temperature.”
What did you do – The bubble is a fascinating revelation of a piece of outlier data.
The new study is based on observations from the Atacama Large Millimeter/submillimeter Array (ALMA), named after the Chilean desert where it was built. ESO, which posted an advertisement for the new job, manages this site. Wielgus says that ALMA observed Sgr A* for EHT on April 6 and 7, 2017, and then, a few days later, ALMA observed the black hole again. But that data from April 11 was not incorporated into the first image of Sagittarius A*.
“We avoided using the third day with ALMA [April 11] for the EHT results, precisely because we knew there was an X-ray flash that day, and we saw some indication of increased source variability, says Wielgus. “So it’s probably not good for reconstruction of a static average image.”
This is what EHT revealed on May 12, 2022. The team produced a main image by averaging thousands of images. Keep the common features and remove the ones that don’t usually appear.
Whats Next – Think of the fabulous May 2022 image as a portrait, which Wielgus says “showed us Sgr A* on a quiet and peaceful day.” The new work is exciting because it is a vibrant screenshot of an action-packed scene. With this “glimpse of the Sgr A* flare” comes the opportunity to develop a better model of the supermassive black hole.
X-ray data from NASA’s Chandra X-ray Observatory in space and infrared data from the GRAVITY instrument with the Very Large Telescope Interferometer (VLTI) in Chile had previously detected the flares. But now that new radio observations from the recent study are available, it provides a new layer for scientists to explore.
Hopefully, all of this adds up to a solid understanding of the heart of the Milky Way that was previously impossible to obtain.