Astrophysics: The heart of darkness
Nature 505, 7483 (2014). http://www.nature.com/doifinder/10.1038/505280a
Author: Ron Cowen
The supermassive black holes that lie at the centre of every large galaxy are full of mysteries. But astronomers are finally getting a clear look.
Astronomy: The great unseen
Nature 505, 7483 (2014). doi:10.1038/505290a
Author: Eric Hand
Eric Hand views a planetarium show on dark matter and dark energy that is both dislocating and transfixing.
Astrophysics: Black hole found orbiting a fast rotator
Nature 505, 7483 (2014). doi:10.1038/505296a
Authors: M. Virginia McSwain
Stars of spectral type 'Be' are often found with neutron stars or other evolved analogues, but a black-hole companion has never been spotted before. Optical emission from a black hole's surroundings has given it away. See Letter p.378
A Be-type star with a black-hole companion
Nature 505, 7483 (2014). doi:10.1038/nature12916
Authors: J. Casares, I. Negueruela, M. Ribó, I. Ribas, J. M. Paredes, A. Herrero & S. Simón-Díaz
Stellar-mass black holes have all been discovered through X-ray emission, which arises from the accretion of gas from their binary companions (this gas is either stripped from low-mass stars or supplied as winds from massive ones). Binary evolution models also predict the existence of black holes accreting from the equatorial envelope of rapidly spinning Be-type stars (stars of the Be type are hot blue irregular variables showing characteristic spectral emission lines of hydrogen). Of the approximately 80 Be X-ray binaries known in the Galaxy, however, only pulsating neutron stars have been found as companions. A black hole was formally allowed as a solution for the companion to the Be star MWC 656 (ref. 5; also known as HD 215227), although that conclusion was based on a single radial velocity curve of the Be star, a mistaken spectral classification and rough estimates of the inclination angle. Here we report observations of an accretion disk line mirroring the orbit of MWC 656. This, together with an improved radial velocity curve of the Be star through fitting sharp Fe ii profiles from the equatorial disk, and a refined Be classification (to that of a B1.5–B2 III star), indicates that a black hole of 3.8 to 6.9 solar masses orbits MWC 656, the candidate counterpart of the γ-ray source AGL J2241+4454 (refs 5, 6). The black hole is X-ray quiescent and fed by a radiatively inefficient accretion flow giving a luminosity less than 1.6 × 10−7 times the Eddington luminosity. This implies that Be binaries with black-hole companions are difficult to detect in conventional X-ray surveys.
From cleanroom to liftoff, watch an incredible time-lapse movie of Gaia's final preparations on Earth before shooting for the stars.
Kepler clue to supernova puzzle
Nature 505, 7483 (2014). http://www.nature.com/doifinder/10.1038/505274a
Author: Ron Cowen
Two white dwarfs favoured as precursors of type Ia supernovae.