Cloudlets Swarm Around our Local Supermassive Black Hole

This image from the Atacama Large Millimeter/submillimeter Array (ALMA) shows the area surrounding Sagittarius A*, the supermassive black hole that lurks at the center of the Milky Way — highlighted here with a small circle. New research has revealed exciting evidence of interstellar gas and dust orbiting the black hole at high speeds. 

Credit: ALMA (ESO/NAOJ/NRAO)/ J. R. Goicoechea (Instituto de Física Fundamental, CSIC, Spain)

The molecular-hydrogen-rich gas clouds which have been identified are known as molecular cloudlets, and they have never before been unambiguously detected. This image actually shows the distribution of molecules including carbon monoxide, the cloudlets’ second most abundant molecular component. The cloudlets lie 26 000 light-years away from us, orbiting fast and relatively close to the black hole, at a distance of about one light year. ALMA’s high resolution allowed scientists to detect the cloudlets, which are the products of pre-existing massive clouds rotating around the center of our galaxy. These clouds were tidally disrupted into dense fragments and a lower density, short-lived component. The latter was identified thanks to the signs left by the passage of the synchrotron radiation emitted by Sagittarius A* through the diffuse gas between the cloudlets. 

This ALMA image shows the central 2 parsecs of the Milky Way, with Sag. A* circled in the middle. Blue represents carbon monoxide and red represent hydrogen cyanide. The dotted blue and lines represent inner and outer circular orbits around the black hole. The dotted green lines represent elliptical orbits previously proposed to fit the motion of the ionized gas streamers. The motions of the CO and HCN cloudlets follow neither orbit. Image: ALMA, Goicoechea et. al. 2019.

Although clouds of molecular gas have the potential to form new stars, these cloudlets are unlikely to create stellar newborns. They have a comparatively small mass of around 60 times that of the Sun, and exist close to the huge, turbulent, punishing gravitational forces exerted by Sagittarius A*. 

While the stars orbiting Sagittarius A* have been systematically observed; these dense molecular cloudlets have not been detected so close to the center of our galaxy before. 

This image shows red and magenta carbon monoxide cloudlets around the central black hole. The black contour lines are the ionized gas streamers, the dominant structure this close to the black hole. The cloudlets don’t conform to the orbits and velocities of the streams of gas. Image: ALMA, Goicoechea et. al. 2019.

Scientific Paper

Source: ALMA, ALMA, Universe Today,