The Nearest Black Hole

Kareem El-Badry (Harvard-CfA; Max Planck IfA) and collaborators have used GMOS on Gemini North to help identify a 9.62 ± 0.18 M⊙ black hole (BH) only 480 pc distant. This object, informally designated as Gaia BH1, is now the closest black hole known by a factor of three. Unlike nearly all known ‘stellar-mass’ BHs, that is, those having masses < ~100 M⊙, Gaia BH1 was not detected by X-ray emission powered by gas accreted from a nearby, tightly bound, stellar companion. It is presently quiescent and was only identified by its astrometric perturbation of a Sun-like star orbiting it at a distance of 1.44 ± 0.11 AU.