Subaru Telescope | National Astronomical Observatory of Japan | 2015 Jun 25
Using the Subaru Telescope, researchers at the Special Astrophysical Observatory in Russia and Kyoto University in Japan have found evidence that enigmatic objects in nearby galaxies – called ultra-luminous X-ray sources (ULXs) – exhibit strong outflows that are created as matter falls onto their black holes at unexpectedly high rates. The strong outflows suggest that the black holes in these ULXs must be much smaller than expected. Curiously, these objects appear to be "cousins" of SS 433, one of the most exotic objects in our own Milky Way Galaxy. The team's observations help shed light on the nature of ULXs, and impact our understanding of how supermassive black holes in galactic centers are formed and how matter rapidly falls onto those black holes.
X-ray observations of nearby galaxies have revealed these exceptionally luminous sources at off-nuclear positions that radiate about million times higher power than the Sun. The origins of ULXs have been a subject of heated debate for a long time. The basic idea is that a ULX is a close binary system consisting of a black hole and a star. As matter from the star falls onto the black hole, an accretion disk forms around the black hole. As the gravitational energy of the material is released, the innermost part of the disk is heated up to a temperature higher than 10 million degrees, which causes it to emit strong X-rays.
The unsolved key question about these objects asks: what is the mass of the black hole in these bright objects? ULXs are typically more than a hundred times more luminous than known black hole binaries in the Milky Way, whose black hole masses are at most 20 times the mass of the Sun. ...
Supercritical accretion disks in ultraluminous X-ray sources and SS 433 - Sergei Fabrika et al
- Nature Physics (online 01 Jun 2015) DOI: 10.1038/nphys3348