Microlensing Mystery

This spectacular starry field of view shows the globular cluster NGC 6553 which is located approximately 19 000 light-years away in the constellation of Sagittarius. In this field, astronomers discovered a mysterious microlensing event.

Microlensing is a form of gravitational lensing in which the light from a background source is bent by the gravitational field of a foreground object, creating an amplified image of the background object. The object causing the microlensing in NGC 6553 bent the light of a red giant star in the background (marked with an arrow). If this object lies in the cluster, the object could be a black hole with a mass twice that of the Sun, making it the first of its kind to be discovered in a globular cluster. 

Credit: ESO