09/12/2019: Nature paper: A wide star–black-hole binary system from radial-velocity measurements

Exciting new results from observations of a star orbiting a massive black hole, published in a recent Nature paper.
Observation of the radial velocity variations of a Galactic star suggest it is orbiting a black hole, in a first taste of how the Galactic black-hole population could be revealed by future time-domain spectroscopic surveys. The visible star is inferred to be a B-type star with a mass roughly 8 times greater than that of the Sun; this star is in a circular orbit with a period of 78.9 days around an unseen mass. Together this indicates a system containing a black hole of at least 6 solar masses, and one which is wider than any previously known Galactic black-hole binary.

The most exciting possibility comes If a H-alpha emission line from the system is interpreted as indicating the motion of the black hole. In that case then the black hole is inferred to have a mass of 68 solar masses. This is highly unexpected. Even though gravitational wave experiments have detected similarly massive black holes, forming black holes as massive as that in high-metallicity environment would be extremely challenging to current evolution theories.

GRAPPA & API member Stephen Justham is one of the co-authors on the paper. Read the full paper.