Based on the assumptions about the mass, the Notre Dame researchers estimate that one of the black holes is about 6,600 light-years from Earth. Each light year equals about 6 trillion miles or 10 trillion kilometers. Until now, black holes have been detected only as part of a multiple-star system or at the center of galaxies. The new observations help confirm the theory that black holes can form all by themselves through the collapse of isolated massive stars. Hubble provided additional images last year.
Scientists believe the unseen object is a black hole.
The astronomers'microlensing technique watches the sky for light distortions caused when a dark object passes in front of a more distant field of stars. Careful analysis of the distortion patterns can yield information about the distance and mass of the unseen object in the middle. About 300 microlensing events have been recorded so far, some of them hinting at the existence of unseen planets or burned-out stars.