Lone black holes promise fresh insights into the fates of massive stars

In 1971, the first black hole ever found revealed itself when astronomers glimpsed a blue star racing around an invisible object (1).The dark partner was so massive that it had to be a black hole-an ultradense collapsed star.Theorists had long predicted that black holes could exist somewhere in space.Since that discovery, luminous stars orbiting dark bodies have betrayed the presence of about two dozen other black holes in our galaxy.These objects, with several times the mass of the Sun, are known as stellar-mass black holes.But a recent discovery represents a remarkable exception: It's a loner, unbound to any star."Nobody had ever detected any isolated black hole," says Kailash Sahu, an astronomer at the Space Telescope Science Institute in Baltimore, MD.Isolated black holes vastly outnumber those with luminous partners, researchers think, and thus promise to provide a better portrait of the entire black hole population.Finding more could therefore yield new insights into black hole masses, as well as which stars produce them.At first glance, the quest to spot more loners seems impossible.Not only does a black hole emit no light, but a solitary black hole also fails to tug a companion star that observers can see.Nevertheless, Sahu came up with a clever plan to nab the first one, and, within the next year, NASA expects to launch a new space telescope that will pursue the same strategy."It has the potential to find a lot of black holes," says Kareem El-Badry, an astronomer at the California Institute of Technology in Pasadena.