Alma discovers hot gas near our black hole

nNothing travels faster than light, according to Einstein, and if something reaches 30% of the speed of light, there must be unimaginable forces for such acceleration—like near Sagittarius A*, the supermassive black hole at the center of our galaxy. With the help of the Chilean ALMA observatory, astronomers have now observed a mass of hot gas orbiting the center of our galaxy at a distance of five times the Schwarzschild radius in just 70 minutes – that is, with an orbital radius of about 60 million km, which roughly corresponds to Mercury.

Researchers about Maciek Wielgus from Bonner Max Planck Institute For radio astronomy presented these results Now in “Astronomy and Astrophysics”. The Event Horizon Telescope (EHT), a global network of eight radio observatories, only published the first image of arc A* this spring. As part of these observations, ALMA data that has now been evaluated was also recorded in 2017. Coincidentally, some of the observations occurred shortly after a burst of X-ray waves was detected at the galactic center. These explosions are attributed to bubbles of hot gas orbiting the black hole very quickly and in close proximity.

ALMA’s observations now provide evidence for the first time of such an event at radio wavelengths – and also that the radiation burst has a magnetic origin. Namely, millimeter data contains information about the magnetic field of the arc A* in the form of the direction of vibration of the received radiation. Using a dynamic emission model, the motion of the gas bubble and even the properties of the black hole and its surroundings can be reconstructed from observations. According to this, there is evidence of a black hole’s positive angular momentum and a clockwise rotating disk structure where the magnetic field prevents the gas swirling in the black hole from moving in such a way that bubbles and streams form.

Astronomers now expect more insights from comparison with observations in the infrared, notably with the Max Planck Institute for Extraterrestrial Physics’ GRAVITY instrument installed at ESO’s Very Large Telescope Interferometer (VLTI) in Chile. The gas bubbles, which were initially visible in the infrared, can be seen at radio wavelengths once they have cooled enough. According to the authors, in order to relate data recorded at different wavelengths to each other, these observations must be made simultaneously in a future-targeted manner.