Texas astronomers "weigh" heaviest known black hole in our cosmic neighborhood

Astronomers led by Karl Gebhardt of The University of Texas at Austin have measured the most massive known black hole in our cosmic neighborhood by combining data from a giant telescope in Hawai'i and a smaller telescope in Texas.

Artist's concept of what a future telescope might see in looking at the black hole at the heart of the galaxy M87. A high-resolution version of this illustration with extended caption, plus video and more graphics, are available from the McDonald Observatory. Credit: Gemini Observatory/AURA illustration by Lynette

The result is an ironclad mass of 6.6 billion suns for the black hole in the giant elliptical galaxy M87. This enormous mass is the largest ever measured for a black hole using a direct technique. Given its massive size, M87 is the best candidate for future studies to "see" a black hole for the first time, rather than relying on indirect evidence of their existence as astronomers have for decades.

The results will be presented in a news conference today at the 217th meeting of the American Astronomical Society in Seattle. Two papers detailing the results will be published soon in The Astrophysical Journal.

Gebhardt, the Herman and Joan Suit Professor of Astrophysics, led a team of researchers using the 8-meter Gemini North telescope in Hawai'i to probe the motions of stars around the black hole in the center of the massive galaxy M87.

University of Texas at Austin graduate student Jeremy Murphy has used the Harlan J. Smith Telescope at the university's McDonald Observatory in West Texas to probe the outer reaches of the galaxy - the so-called "dark halo." The dark halo is a region surrounding the galaxy filled with "dark matter," an unknown type of mass that gives off no light but is detectable by its gravitational effect on other objects.

In order to pin down the black hole's mass conclusively, Gebhardt says, one must account for all the components in the galaxy. Studies of the central and outermost regions of a galaxy are necessary to "see" the influence of the dark halo, the black hole and the stars. But when all of these components are considered together, Gebhardt says, the results on the black hole are definitive, meeting what he calls the "gold standard" for accurately sizing up a black hole.