January 13, 2000
Photo No: H2000-03
Lone Black Hole Passes in Front of Star
[Left] (Not shown)
Two images of a crowded starfield as seen through a ground-based
telescope show the subtle brightening of a star due to the effect
of gravitational microlensing, where an invisible but massive
foreground object passes in front of the star and amplifies its
light. The dark lensing object is estimated to be a six-solar-mass
black hole that is drifting alone among the stars.
Credit: NOAO, Cerro Tololo Inter-American Observatory
A NASA Hubble Space Telescope image of the same field clearly
resolves the lensed star and yields its true brightness. The
Hubble observation was needed because the ground-based images
do not tell how bright the lensed star actually was before
(or after) it was lensed. The star fields where microlensing
events are observed are so crowded with stars that the
lensed star images are often blended together with images of
unlensed stars. But with the Hubble images, astronomers can
identify the lensed star and determine its normal brightness.
The Hubble images were taken on June 15, 1999.
Credit: NASA and Dave Bennett (University of Notre Dame, Indiana)