Follow UsDetecting Isolated Black Holes through Astrometric Microlensing
HST Proposal 15318
Kailash Sahu (publications @ ADS)
Eureka Scientific Inc.
Category: Stellar Physics
Proposal type: GO
Status: completed
Proposal Abstract
A significant fraction of the mass of an old stellar population should be in the form of isolated black holes (BHs). Yet there has never been an unambiguous detection of a solitary BH. The only technique available to detect isolated BHs is astrometric microlensing--relativistic deflection of light from background stars. We have carried out 2 HST programs aimed at the first detection of isolated BHs through astrometric microlensing. Our first program was a multi-year program where we monitored 5 microlensing events with T>100 days in the Galactic bulge. We detected astometric deflections, but the inferered masses for all these events are <0.5 Msun, indicating that these lenses are low-mass stars with small relative proper motions. Our second program was a large multi-cycle program where we monitored ~3 million stars in the Galactic bulge for 3 years to simultaneously detect microlensing events and deterimne their astrometric shifts. We have detected a large number of microlensing events. However, once again, none of them show appreciable astrometric deflections indicative of massive BHs. Our results imply that either isolated BHs are more massive (>10 Msun), or T~100 day events are dominated by low-mass stars moving more slowly, or BHs are much rarer. BHs with mass > 10 Msun are expected to have T>300 days, and such very-long duration events are extremely unlikely to be caused by low-mass stars. Monitoring a few T>300-day events thus offers the last but most promising opportunity to detect isolated BHs, and distinguish between the above possibilities. After the recent upgrades, OGLE detects six T>300 days events each year, here we propose to monitor 4 such events.
Publications referencing this proposal
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