Starship Asterisk*

[img3="Quasar Host Galaxy Markarian 231
Credit: NASA, ESA, Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration,
and A. Evans (Univ of Virginia, Charlottesville/NRAO/Stony Brook Univ)"]http://imgsrc.hubblesite.org/hu/db/imag ... ge_web.jpg[/img3][hr][/hr]

Astronomers using NASA's Hubble Space Telescope have found that Markarian 231 (Mrk 231), the nearest galaxy to Earth that hosts a quasar, is powered by two central black holes furiously whirling about each other.

The finding suggests that quasars — the brilliant cores of active galaxies — may commonly host two central supermassive black holes that fall into orbit about one another as a result of the merger between two galaxies. Like a pair of whirling skaters, the black-hole duo generates tremendous amounts of energy that makes the core of the host galaxy outshine the glow of the galaxy's population of billions of stars, which scientists then identify as quasars.

Scientists looked at Hubble archival observations of ultraviolet radiation emitted from the center of Mrk 231 to discover what they describe as "extreme and surprising properties."

If only one black hole were present in the center of the quasar, the whole accretion disk made of surrounding hot gas would glow in ultraviolet rays. Instead, the ultraviolet glow of the dusty disk abruptly drops off towards the center. This provides observational evidence that the disk has a big donut hole encircling the central black hole. The best explanation for the observational data, based on dynamical models, is that the center of the disk is carved out by the action of two black holes orbiting each other. The second, smaller black hole orbits in the inner edge of the accretion disk, and has its own mini-disk with an ultraviolet glow. ...

• Astrophysical Journal 809(2):117 (2015 Aug 10) DOI: 10.1088/0004-637X/809/2/117
  arXiv.org > astro-ph > arXiv:1508.06292 > 25 Aug 2015

This provides observational evidence that the disk has a big donut hole encircling the central black hole. The best explanation for the observational data, based on dynamical models, is that the center of the disk is carved out by the action of two black holes orbiting each other.