NOAO >   Observing Info >   Approved Programs >   2011A-0460

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Proposal Information for 2011A-0460


PI: Kailash Sahu, Space Telescope Science Institute, ksahu@stsci.edu
Address: Science Missions Office, 3700 San Martin Drive, Baltimore, MD 21218, USA

CoI: Howard Bond, Space Telescope Science Institute
CoI: Jay Anderson, Space Telescope Science Institute
CoI: Martin Dominik, University of St. Andrews
CoI: Andrzej Udalski, Warsaw University
CoI: Michael Albrow, University of Canterbury

Title: Detecting Isolated Black Holes through Astrometric Microlensing

Abstract: Our aim is the first detection of isolated stellar-mass black holes (BHs). We have underway an \it HST project of precision astrometry of long-duration microlensing events in the Galactic bulge. Such long events can be produced by BH lenses, or occasionally by low-mass lenses moving with unusually low velocities. To distinguish between them, we are using \it HST WFC3 imaging to detect the astrometric shift that occurs only in the case of a BH-mass lens. We will monitor a total of 6 microlensing events with \HST, and the first 3 such campaigns are already underway. For the first event, we have already detected an astrometric shift of ~1.8 mas, implying a lens mass of 10-40 M_\odot\null. However, the astrometric shift depends not only on the lens mass, but also on the distances to the lens and the source. The distance to the lens can be inferred from the effect of the Earth's motion on the microlensing light curve. In this proposal we request 6 hours of spectroscopic observations (over 2 semesters) in order to determine the spectral types of the sources and remove the remaining uncertainty. The types will lead to estimates of their extinction and distances, accurate determination of the lens masses, and confirmation that we have detected the first isolated black holes.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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