A supermassive black hole in the center of the Milky Way has hosted a very real “party” accompanied by a disco ball-style light show. This is evidenced by data collected by the James Webb Telescope (JWST).
Amazing black hole activity
At the center of our galaxy lurks a supermassive object known as Sagittarius A*. It’s a black hole whose mass is four million times that of the sun. It is surrounded by an accretion disk consisting of matter heated to very high temperatures, which is a powerful source of radiation.
A team of researchers from Northwestern University in Illinois decided to use the JWST to study the activity of Sagittarius A*. The choice is explained by the fact that JWST can capture infrared waves, which, unlike visible light, pass through the dust clouds that fill the center of the Milky Way.
The results of the observations surprised the scientists. They expected to see flares, but Sagittarius A* turned out to be much more active than expected. Its accretion disk produces a constant stream of flares with no quiescent periods. Black hole activity occurs over a wide range of times, from short interludes to long stretches. Some flares are faint flickers lasting seconds, while others are dazzlingly bright eruptions that occur daily. There are even weaker changes that occur over a period of months. On average, the accretion disk generates five to six large flares per day and several smaller sub- flares or bursts in between.
Two different processes within Sagittarius A*
Although scientists do not yet fully understand the processes involved, they propose that two separate processes are responsible for the shorter and longer flares. Small perturbations in the accretion disk likely cause faint flickers. In particular, turbulent oscillations within the disk can compress the plasma and cause temporary bursts of radiation. These events are somewhat similar to solar flares.
Large flares, on the other hand, result from magnetic reconnection, a process where two magnetic fields collide, releasing energy in the form of accelerated particles. Moving at close to the speed of light, these particles emit bright bursts of radiation. In turn, such events are something like a spark of static electricity.
Time delay
Since the NIRCam camera mounted on JWST is capable of simultaneously observing in two different wavelength ranges (2.1 and 4.8 microns in this case), the scientists were able to compare how the brightness of the flares varied with wavelength. And the researchers were once again surprised. They found that events observed at shorter wavelengths change brightness slightly earlier than events at longer wavelengths. The time delay ranged from a few to 40 seconds.
This time delay gave more clues about the physical processes going on around the black hole. One explanation is that the particles lose energy during the flare, and it is lost faster at short wavelengths than at long wavelengths. Such changes are expected for particles revolving around magnetic field lines.
The findings may help physicists better understand the fundamental nature of black holes, how they are powered, and the dynamics and evolution of our own galaxy. They hope that they will again be able to use JWST to observe Sagittarius A* for a longer period of time, which will help reduce noise and allow even finer details to be seen.
Earlier we reported on a mysterious object discovered by astronomers, it resists being swallowed by a black hole.
According to NASA
