“A nearby black hole is hurtling like a cannonball through the disk of our galaxy. The detection of this speed demon is the best evidence yet, some astronomers say, that stellar-mass black holes — those that are several times as massive as the Earth’s Sun — are created when a dying, massive star explodes in a violent supernova. The stellar-mass black hole, called GRO J1655-40, is streaking across space at a rate of 250,000 miles per hour, which is four times faster than the average velocity of the stars in that galactic neighborhood. At that speed, the black hole may have been hurled through space by a supernova blast….

GRO J1655-40 is the second so-called ‘microquasar’ discovered in our Galaxy. Microquasars are black holes of about the same mass as a star. They behave as scaled-down versions of much more massive black holes that are at the cores of extremely active galaxies, called quasars. Astronomers have known about the existence of stellar-mass black holes since the early 1970s. Their masses can range from 3.5 to approximately 15 times the mass of our Sun.” NASA STScI