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How Do Black Holes Do It?

by WKT

September 18, 2006 ::

By "it," we mean, put so much energy out into the Universe. Observations with Chandra and other telescopes imply that up to a quarter of the total radiation in the Universe emitted since the Big Bang come from material falling toward black holes, especially the supermassive varieties. That's quite an accomplishment for objects that represent the Universe's ultimate sinkhole from which nothing can escape. This past year, observations with Chandra have shed light on the fascinating question of how black holes help to light up the Universe.

Chandra Image of MS 0735.6+7421
Chandra Image of MS 0735.6+7421
Credit: NASA/CXC/Ohio U./B.McNamara
Illustration of a Stellar-Mass Black Hole
Illustration of a Stellar-Mass Black Hole
Illustration: NASA/CXC/M.Weiss; X-ray Spectrum: NASA/CXC/U.Michigan/J.Miller et al.
Short Answer: Gravity + Disk of Gas
The short answer has been known for years - the enormous gravity of a black hole pulls surrounding gas toward it and accelerates it to very high energies. As the gas forms in a disk and spirals toward the black hole, a portion of the energy of the gas is somehow expelled from the vicinity of the black hole before the matter passes beyond the event horizon - the cosmic manhole cover over the cosmic sinkhole.

Longer Answer: Gravity + Disk of Gas + Magnetic Fields
Computer simulations indicated that the "somehow" part of the explanation involves magnetic fields embedded in the gas. The magnetic fields help to generate friction in a disk of swirling gas around a black hole. This friction heats the gas and causes it to spiral inward, emitting X-rays in the process. Magnetic fields also can drive gas away from the black hole in winds and high-speed jets. Chandra observations of a wind from a black hole disk have confirmed this general picture.

Chandra Image of the Perseus Cluster
Chandra Image of the Perseus Cluster
Credit: NASA/CXC/IoA/A.Fabian et al.
Chandra Image of NGC 4696
Chandra Image of NGC 4696
Credit: X-ray: NASA/CXC/KIPAC/S.Allen et al; Radio: NRAO/AUI/NSF/G.Taylor; Infrared: NASA/ESA/McMaster Univ./W.Harris
Not Only Light, But Action
Chandra data from galaxies containing active supermassive black holes indicate that much of the energy released by the infalling gas goes, not just into an outpouring of light but also into jets of high-energy particles. Such jets can be launched from a magnetized gaseous disk around the central black hole, and blast away at near the speed of light. By stirring up the gas in the outer reaches of a galaxy and beyond, jets generated by supermassive black holes can have an important effect on how stars form in the galaxy, determine the ultimate shape of the galaxy, and even reheat intergalactic gas in galaxy clusters.

The Ultimate Hybrid - A Billion Miles Per Gallon
The recent work on black holes shows that the conversion of energy by matter falling toward a black hole is much more efficient than nuclear energy or fossil fuels. For example, it has been estimated that if a car was as fuel-efficient as some black holes, it could travel more than a billion miles per gallon!

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