A flare observed from the supermassive black hole at the center of the Milky Way

The central area of ​​the Milky Way with SgrA*
An article accepted for publication in the journal “Astronomy & Astrophysics” reports a study on Sagittarius A*, or SgrA*, the supermassive black hole at the center of the Milky Way, observed during a flare after it swallowed gas and dust in large quantities. A team of researchers used observations conducted simultaneously in 2019 with the GRAVITY instrument on ESO’s VLT interferometer and with the Spitzer, NuSTAR, and Chandra space telescopes to obtain infrared and X-ray data of the flare. This made it possible to create a detailed model of that type of flare.

The supermassive black hole at the center of the Milky Way has a mass estimated to be just over four million times the Sun’s. The image (X-ray: NASA/CXC/UMass/D. Wang et al.; Optical: NASA/ESA/STScI/D.Wang et al.; IR: NASA/JPL-Caltech/SSC/S.Stolovy) shows the central area of ​​the Milky Way with SgrA* in a combination of X-rays in blue, optical frequencies in yellow, and infrareds in red.

SgrA* isn’t very active compared to quasars, which are surrounded by large amounts of materials, but there are still some gas clouds around it. Occasionally it attracts enough gas to swallow it in quantity and generate a flare. It’s a situation studied over the years and reported for example in an article published in the journal “Astronomy & Astrophysics” in October 2018.

Studies continue, and in July 2019 a consortium of scientific entities conducted a campaign of simultaneous observations with the GRAVITY instrument on ESO’s VLT interferometer and with the Spitzer, NuSTAR, and Chandra space telescopes. This also made it possible to obtain infrared and X-ray data of a flare that occurred in that period.

The observations made it possible to observe the processes taking place around SgrA* to test existing models. In one possible process, electrons at relativistic speeds moving in magnetic fields emit photons in what is called synchrotron radiation. In a second possible process, photons produced in various ways receive energy from electrons in the mechanism known as the inverse Compton scattering. The interesting result is that both processes appear to take place in these flares: according to the researchers, infrared emissions are generated by synchrotron radiation while X-ray emissions are generated by inverse Compton scattering.

This study will help improve existing models for supermassive black hole flares thanks to the detail that can be obtained from the area around SgrA*. Currently, the models describe the various aspects of flare emissions quite well, but several parts connected with the physics behind particle acceleration are still missing. Studying extreme environments such as these could provide valuable information for making progress in bringing together quantum physics and relativistic physics.

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