How did Supermassive Black Holes Grow so Massive so Quickly?

Friday, August 15, 2014

How did Supermassive Black Holes Grow so Massive so Quickly?

How did Supermassive Black Holes Grow so Massive so Quickly?:

Artist concept of matter swirling around a black hole. (NASA/Dana Berry/SkyWorks Digital)

An artist’s conception of a swirling accretion disk around a black hole. Credit: NASA / Dana Berry / SkyWorks Digital

Black holes one billion times the Sun’s mass or more lie at the heart of many galaxies, driving their evolution. Although common today, evidence of supermassive black holes existing since the infancy of the Universe, one billion years or so after the Big Bang, has puzzled astronomers for years.

How could these giants have grown so massive in the relatively short amount of time they had to form? A new study led by Tal Alexander from the Weizmann Institute of Science and Priyamvada Natarajn from Yale University, may provide a solution.

Black holes are often mistaken to be monstrous creatures that suck in dust and gas at an enormous rate. But this couldn’t be further from the truth (in fact the words “suck” and “black hole” in the same sentence makes me cringe). Although they typically accumulate bright accretion disks — swirling disks of gas and dust that make them visible across the observable Universe — these very disks actually limit the speed of growth.

First, any infalling matter can only enter through the accretion disk. Second, as matter in an accretion disk gets close to the black hole, traffic jams occur that slow down any other infalling material. And third, as matter collides within these traffic jams, it heats up, generating energy radiation that actually drives gas and dust away from the black hole.

A star or a gas stream can actually be on a stable orbit around the black hole, much as a planet orbits around a star. So it is quite a challenge for astronomers to think of ways that would make a black hole grow to supermassive proportions.

Luckily, Alexander and Natarajan may have found a way to do this: by placing the black hole within a cluster of thousands of stars, they’re able to operate without the restrictions of an accretion disk.

Black holes are generally thought to form when massive stars, weighing tens of solar masses, explode after their nuclear fuel is spent. Without the nuclear furnace at its core pushing against gravity, the star collapses. While the inner layers fall inward to form a black hole of only about 10 solar masses, the outer layers fall faster, hitting the inner layers, and rebounding in a huge supernova explosion. At least that’s the simple version.

A small black hole gains mass: Dense cold gas (green) flows toward the center of a stellar cluster (red cross in blue circle) with stars (yellow); the erratic path of the black hole through the gas (black line) is randomized by the surrounding stars Prof. Tal Alexander’s research is supported by the European Research Council.

The erratic path of the black hole through the gas (black line) is randomized by the surrounding stars (yellow circles). Meanwhile, dense cold gas (green arrows) flows toward the center of the cluster (red cross). Credit: Weizmann Institute of Science.

The team began with a model of a black hole, created from this stellar blast, embedded within a cluster of thousands of stars. A continuous flow of dense, cold, opaque gas fell into the black hole. But here’s the trick: the gravitational pull of many nearby stars caused it to zigzag randomly, preventing it from forming an accretion disk.

Without an accretion disk, not only is matter able to fall into the black hole from all sides, but it isn’t slowed down in the accretion disk itself.

All in all, the model suggests that a black hole 10 times the mass of the Sun could grow to more than 10 billion times the mass of the Sun by one billion years after the Big Bang.

The paper was published Aug. 7 in Science and is available online.

Tagged as:
Black Holes,
Cosmology,
Early Universe,
quasars

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The National Aeronautics and Space Administration (NASA) is the United States government agency responsible for the civilian space program as well as aeronautics and aerospace research. President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA's predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

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Photos of Nature | Nature Photography What is The Universe

Friday, August 15, 2014