The Sciences

We Knew Black Holes Were Massive. Now Double That.

By Eliza StricklandJun 9, 2009 11:27 PM
M87 galaxy


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Researchers have recalculated the mass of a gigantic black hole at the core of the M87 galaxy, and found that it’s about two times as massive as previously estimated: The new study says that M87’s black hole weighs the same as 6.4 billion suns. Researchers say the findings may indicate that many black holes have been underestimated, and also say that the results from this “local” galaxy only 50 million light-years away may solve a mystery regarding the extremely distant black holes known as quasars.

Astronomers had previously estimated M87’s total mass, calculating how much of that mass came from both the galaxy’s stars and its central black hole. But previous models didn’t have the supercomputing power to estimate the mass contributed by the galaxy’s “dark halo.” The dark halo is a spherical region surrounding the galaxy that extends beyond its main visible structure. It contains “dark matter”, an as yet unidentified material that cannot be directly detected by telescopes but which astronomers know is there from its gravitational interaction with everything else that can be seen [BBC News].

For the new study, which was presented at the American Astronomical Society meeting and will be published later this year in the Astrophysical Journal, researchers employed the gargantuan computing power of the Lonestar system … at the University of Texas. The Lonestar has 5,840 processing cores and can perform 62 trillion “floating-point operations” per second. For comparison, the most state-of-the-art laptop computer has only two processing cores and performs only 10 billion such operations per second [AFP].

With that computational firepower, researchers determined that a large bulk of the mass initially thought to belong to stars at M87’s core is actually locked up in the halo at the galaxy’s outer edge. But the actual mass of the core is still thought to be the same. So if the extra mass isn’t tied up in stars, it must belong to the supermassive black hole, Gebhardt explained [National Geographic News]. While this new calculation of the black hole’s mass was determined solely via computer modeling, researcher Karl Gebhardt says that not-yet-published observations from the world’s most sophisticated telescopes back up his findings.

The new numbers also make sense of previous observations of quasars, the distant black holes that shine brightly as material spirals towards the black hole’s event horizon–the point beyond which nothing, not even light, can escape. These quasars were believed to be colossal, around 10 billion solar masses, “but in local galaxies, we never saw black holes that massive, not nearly,” Gebhardt said. “The suspicion was before that the quasar masses were wrong,” he said []. Now, by boosting the mass of local black holes, researchers have bolstered the case for prior estimations of the quasars’ mass.

Image: NASA/CXC/CfA/W. Forman et al./NRAO/AUI/NSF/W. Cotton;/ESA/Hubble Heritage Team (STScI/AURA), and R. Gendler. The M87 galaxy. 

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