Hubble is astronomy's preeminent "black hole hunter" because of its unique ability to use its Space Telescope Imaging Spectrograph (STIS) camera to precisely measure the speed of gas and stars around a black hole. Hubble is the best way to find lots of black holes without selection biases.

The findings reported at the AAS meeting are based on two types of Hubble observations. Several teams measured the black holes' masses by recording the whirling speeds of disks of gas trapped around the black holes, like water swirling around a drain. Other teams measured the motions of stars around the galaxies' hubs like a swarm of bees hovering around a beehive. The more massive the bulge, the greater the speed of the stars.

Speculation about giant black holes in galaxies began with the discovery of quasars in the 1960s. Astronomers soon realized that the extraordinary gravitational field of a large black hole was the necessary "engine" for generating the prodigious amounts of energy blasted into space by a quasar.

But astronomers realized that the light from a quasar represented only 1/10 of the mass that must be devoured by the black hole. Where was this vast fuel supply coming from? The discovery of many different kinds of active galactic nuclei in the 1970s also required a process of black hole feeding early in a galaxy's life. This meant that black hole accretion is not an incidental process in the life of a galaxy.

But black holes could not be confidently detected in a broad sample of galaxies until Hubble came along with the precise accuracy to measure the velocity of matter trapped close into the black hole and "weigh" its mass.

The research team's next step is to look for the smallest nuclear black holes that can be detected with Hubble. This information will help astronomers understand the mechanism for the seed black holes that grew so rapidly during galaxy formation.

The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. for NASA, under contract with NASA's Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency.