A team of astronomers at the Space Telescope Science Institute, working with one colleague from the University of St Andrews' Center for Exoplanet Science and another from the European Southern Observatory, has confirmed the existence of a lone black hole. In their paper published in The Astrophysical Journal, the group describes how they studied newer data regarding an object they had spotted several years ago to confirm its identity.
Note that you can’t see the black hole in this image (an optical HST image). The black hole was identified through microlensing of the object labeled “source”, followed by subsequent astrometric observations. The black hole is the lens, which is not seen in these images because it’s too faint.