Puzzling accretion onto a black hole in the ultraluminous X-ray source M 101 ULX-1
Nature 503, 7477 (2013). doi:10.1038/nature12762
Authors: Ji-Feng Liu, Joel N. Bregman, Yu Bai, Stephen Justham & Paul Crowther
There are two proposed explanations for ultraluminous X-ray sources (ULXs) with luminosities in excess of 1039 erg s−1. They could be intermediate-mass black holes (more than 100–1,000 solar masses, ) radiating at sub-maximal (sub-Eddington) rates, as in Galactic black-hole X-ray binaries but with larger, cooler accretion disks. Alternatively, they could be stellar-mass black holes radiating at Eddington or super-Eddington rates. On its discovery, M 101 ULX-1 had a luminosity of 3 × 1039 erg s−1 and a supersoft thermal disk spectrum with an exceptionally low temperature—uncomplicated by photons energized by a corona of hot electrons—more consistent with the expected appearance of an accreting intermediate-mass black hole. Here we report optical spectroscopic monitoring of M 101 ULX-1. We confirm the previous suggestion that the system contains a Wolf-Rayet star, and reveal that the orbital period is 8.2 days. The black hole has a minimum mass of 5, and more probably a mass of 20−30, but we argue that it is very unlikely to be an intermediate-mass black hole. Therefore, its exceptionally soft spectra at high Eddington ratios violate the expectations for accretion onto stellar-mass black holes. Accretion must occur from captured stellar wind, which has hitherto been thought to be so inefficient that it could not power an ultraluminous source.
Astronomers using the combined power of NASA's Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA) telescope have discovered a far-flung trio of primitive galaxies nestled inside an enormous blob of primordial gas. The rare triple system existed when the universe was only 800 million years old. The trio may eventually merge into a single massive galaxy, researchers predict. The researchers state that the system provides key insights into the earliest stages of galaxy formation.
Astronomers call for X-ray polarimeter
Nature 503, 7476 (2013). http://www.nature.com/doifinder/10.1038/503325a
Author: Eugenie Samuel Reich
NASA explorer programme raises hopes of mapping directional light from pulsars and black holes.