Alignment of Hubble, Star Cluster and Galactic Bulge for Microlensing Observation
This is a stylized view of a unique Hubble Space Telescope observation to search for low-mass objects residing in the core of the globular star cluster M22 (white clump of stars near image center). Because the objects are too dim to see directly, astronomers used Hubble's sharp view to look right through the cluster to monitor background stars in the Milky Way's central bulge (left). Any intervening object in the cluster will briefly cause a background star to briefly brighten due to the gravitational bending of light as it passes through the foreground cluster. This phenomenon is called microlensing. Hubble is ideally suited for this type of observation, which takes advantage of the telescope's keen ability to study extremely dense regions of stars. The cluster is 8,500 light-years away; the background stars are 30,000 light-years away.
Zolt Levay (STScI)