November 18, 2002: 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.See the rest:
Black holes swallow light and cannot be seen by the human eye. Astronomers tracked the runaway black hole because it has a companion star. NASA Hubble Space Telescope's sharp view allowed astronomers to measure the black hole's motion across the sky. Astronomers already had used ground-based telescopes to measure the black hole's motion toward Earth. They then combined both measurements to obtain the black hole's true velocity.
Astronomers have known about stellar-mass black holes (which range in mass from 3.5 to about 15 suns) since the early 1970s. They form when the core of a doomed star explodes in a violent supernova. The blast sends out a shockwave that rips the rest of the star to shreds. If the surviving core is greater than 3.5 times our Sun's mass, no forces can stop the collapse.