Astronomers this afternoon announced that they have used new computer modeling techniques to discover that the black hole at the heart of M87, one the largest nearby giant galaxies, is two to three times more massive than previously thought. Weighing in at 6.4 billion times the Sun’s mass, it is the most massive black hole yet measured with a robust technique, and suggests that the accepted black hole masses in nearby large galaxies may be off by similar amounts. This has consequences for theories of how galaxies form and grow, and might even solve a long-standing astronomical paradox.
To try to understand how galaxies form and grow, astronomers need start with basic census information about today’s galaxies. What are they made of? How big are they? How much do they weigh? Astronomers measure this last category, galaxy mass, by clocking the speed of stars orbiting within the galaxy.
Studies of the total mass are important, co-researcher Jens Thomas said, but “the crucial point is to determine whether the mass is in the black hole, the stars, or the dark halo. You have to run a sophisticated model to be able to discover which is which. The more components you have, the
more complicated the model is.”
To model M87, Gebhardt and Thomas used one of the world’s most powerful supercomputers, the Lonestar system at The University of Texas at Austin’s Texas Advanced Computing Center. Lonestar is a Dell Linux cluster with 5,840 processing cores and can perform 62 trillion floating-point operations per second. (Today’s top-of-the-line laptop computer has two cores and can perform up to 10 billion floating-point operations per second.)
Extremely massive and conveniently nearby (in astronomical terms), M87 was one of the first galaxies suggested to harbor a central black hole nearly three decades ago. It also has an active jet shooting light out of the galaxy’s core as matter swirls closer to the black hole, allowing astronomers to study the process by which black holes attract matter. Higher masses for black holes in nearby galaxies also could solve a paradox concerning the masses of quasars — active black holes at the centers of extremely distant galaxies, seen at a much earlier cosmic epoch.
Quasars shine brightly as the material spirals in, giving off copious radiation before crossing the event horizon (the region beyond which nothing — not even light — can escape). ”There is a long-standing problem in that quasar black hole masses were very large — 10 billion solar masses,” co-author Karl Gebhardt said. “But in local galaxies, we never saw black holes that massive, not nearly. The suspicion was before that the quasar masses were wrong,” he said. But “if we increase the mass of M87 two or three times, the problem almost goes away.”
Courtesy of 214th meeting of American Astronomical Society in Pasedena, California
Tags: black hole, M87
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