Title: First detection and mass measurement of an isolated black hole through astrometric microlensing

Abstract: We recently detected an isolated stellar-mass black hole (BH) unambiguously for the first time, and measured its mass, distance and velocity. We used HST to carry out precise astrometry of the source star of the long-duration, high-magnification microlensing event OGLE-11-462. Combining HST astrometry, OGLE photometry, and spectroscopic measurements, we obtain a lens mass of ~7 solar mass and a distance of ~1.6 kpc. The lens emits no detectable light, which confirms its BH nature. Its proper motion is offset from the mean motion of Galactic-disk stars at similar distances by ~45 km/s, suggesting that the BH received a natal kick from its supernova explosion. Our mass measurement is the first ever for an isolated stellar-mass BH using any technique. Future telescopes such as Roman should be able to detect a large number of such isolated BHs. 

Astro Colloquium and 'coffee & cookies' department gathering (3:45-4:00pm)

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