Astronomers use supercomputer to resize massive black hole
AFP · 9 Jun 2009, 20:21
Published: 09 Jun 2009 20:21 GMT+02:00
The black hole at the heart of the relatively close Messier 87 Galaxy (M87) weighs in at 6.4 billion times the mass of our Sun, according to US astrophysicist Karl Gebhardt and Germany's Jens Thomas, who say it's the largest ever measured with a reliable technique.
One of the more enigmatic features of astronomy, a black hole is a region in space that is inferred by tracking stars that orbit it. Objects fall into its stupendous gravitational field but nothing, not even light, can return.
Gebhardt and Thomas' revelation, they say, sheds light on how galaxies grow, and may solve the paradox of quasars - active black holes guzzling matter in distant galaxies that scientists are struggling to understand.
Addressing the American Astronomical Society conference in Pasadena, California, the stargazers described how they employed the gargantuan computing power of the Lonestar system, also known as the huge "Texas Advanced Computing Center" 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.
Gebhardt and Thomas's study, to be published later this year in the Astrophysical Journal, aims to clock the mass of Galaxy M87's central black hole by also modeling the galaxy's "dark halo," a phenomenon that extends past a galaxy's visible structure and contains the ethereal but weighty dark matter.
"In the past, we have always considered the dark halo to be significant, but we did not have the computing resources to explore it as well," said Gebhardt as he lauded the supercomputer's ability.
The Lonestar's mass model for the M87 black hole came out several times the weight than any previous estimate, a result they did not expect at all. They chose giant elliptical M87 because of it's relative proximity to our own galaxy - about 55 million light years away. The galaxy is also notable for the spectacularly active jet of light shooting from its core, emitted as matter swirls closer to the black hole. These factors make M87 "the anchor for supermassive black hole studies," Gebhardt said.
The new results, he added, also suggest all other black hole masses for the largest galaxies are grossly underestimated.
Such a conclusion would fundamentally change consideration of the physical laws of space, as scientists examine black holes and probe how galaxies grow. For the problem of weighing quasars, seen at a much earlier period in the vast expanse of cosmic time, the astronomer's conclusion could have major implications.
Quasars shine brightly and emit copious radiation as matter crosses the event horizon - part of the black hole from 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," 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.
Yet, he said, if scientists "increase the mass of M87 two or three times, the problem almost goes away."
While the astronomer's conclusions are model-based, Gebhardt noted that they are supported by his recent physical telescope observations. He has most recently tested the computer simulations by examining M87 and other galaxies through powerful instruments at the Hawaii-based Gemini North Telescope Hilo and the European Southern Observatory's Very Large Telescope in Chile's high altitude Atacama desert.