Starship Asterisk*

[img3="This illustration compares growing supermassive black holes in two different kinds of galaxies. A growing supermassive black hole in a normal galaxy would have a donut-shaped structure of gas and dust around it (left). In a merging galaxy, a sphere of material obscures the black hole (right). Credit: NASA/CXC/M.Weiss/NAOJ"]https://www.jpl.nasa.gov/images/nustar/ ... 509-16.jpg[/img3][hr][/hr]

Black holes get a bad rap in popular culture for swallowing everything in their environments. In reality, stars, gas and dust can orbit black holes for long periods of time, until a major disruption pushes the material in.

A merger of two galaxies is one such disruption. As the galaxies combine and their central black holes approach each other, gas and dust in the vicinity are pushed onto their respective black holes. An enormous amount of high-energy radiation is released as material spirals rapidly toward the hungry black hole, which becomes what astronomers call an active galactic nucleus (AGN).

A study using NASA's NuSTAR telescope shows that in the late stages of galaxy mergers, so much gas and dust falls toward a black hole that the extremely bright AGN is enshrouded. The combined effect of the gravity of the two galaxies slows the rotational speeds of gas and dust that would otherwise be orbiting freely. This loss of energy makes the material fall onto the black hole. ...

The study helps confirm the longstanding idea that an AGN’s black hole does most of its eating while enshrouded during the late stages of a merger. ...

• Monthly Notices of the RAS 468(2):1273 (June 2017) DOI: 10.1093/mnras/stx173
  arXiv.org > astro-ph > arXiv:1701.04825 > 17 Jan 2017 (v1), 20 Mar 2017 (v3)