May 24, 2020

Last Year Our Galaxy’s Black Hole Suddenly Lit Up And Still, Nobody Knows Why

According to a report last year, “On the night of May 13, 2019, UCLA astronomer Tuan Do and his colleagues were watching Sgr A* using the Keck Telescope on the summit of Mauna Kea in Hawai’i. In a period of just two hours, they witnessed the black hole become 75 times brighter in the near-infrared band of the light spectrum.”

A computer-simulated image of a supermassive black hole at the core of a galaxy. Credit: NASA, ESA, and D. Coe, J. Anderson, and R. van der Marel (STScI)

Last year, UCLA Astronomer Tuan Do tweets, “Here’s a timelapse of images over 2.5 hr from May from @keckobservatory of the supermassive black hole Sgr A*. The black hole is always variable, but this was the brightest we’ve seen in the infrared so far. It was probably even brighter before we started observing that night!”

It was obvious that there were was black hole activity occurring, but there was not enough data available at the time to know the details. Vice.com reports that Tuan Do goes on to say, “Maybe the black hole is waking up—there’s a lot we don’t know at this point so we need more data to understand if what we are seeing is a big change in what is feeding the black hole or this is a brief event.”

There are many black holes in the universe. This particular black hole at the center of our galaxy has been followed for a long time. An article on space.com explains, “Astronomers have been watching the black hole at the center of our galaxy for 20 years, and in May, they saw something they’d never seen before.”

The article continues, “Well, technically, they aren’t watching the black hole itself, which scientists call Sagittarius A*, or Sgr A*. Instead, they’re looking at the matter around that black hole. When the Milky Way’s black hole is more active than usual, that event horizon becomes brighter as it heats up due to friction. Usually, Sgr A* is pretty calm for a black hole, but in May, that changed, according to new research.”

“Tracking” a black hole is not a simple or easy thing. NASA explains the process of how black holes are being monitored: “Scientists can’t directly observe black holes with telescopes that detect x-rays, light, or other forms of electromagnetic radiation. We can, however, infer the presence of black holes and study them by detecting their effect on other matter nearby. If a black hole passes through a cloud of interstellar matter, for example, it will draw matter inward in a process known as accretion.

A similar process can occur if a normal star passes close to a black hole. In this case, the black hole can tear the star apart as it pulls it toward itself. As the attracted matter accelerates and heats up, it emits x-rays that radiate into space. Recent discoveries offer some tantalizing evidence that black holes have a dramatic influence on the neighborhoods around them – emitting powerful gamma ray bursts, devouring nearby stars, and spurring the growth of new stars in some areas while stalling it in others.”

What happened last year that made the black hole at center of our galaxy light up? That part, is still up for much debate.