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The Honolulu Advertiser
Posted on: Sunday, August 5, 2007

Galactic cannibalism causes quasars' glow, Hawaii astronomers say

By Jan TenBruggencate
Advertiser Science Writer

The gleam of quasars, the most powerfully radiating objects in the universe, may represent a kind of intergalactic lunch the energy emitted when one galaxy's gas is being gobbled up by the black hole of another galaxy, according to two University of Hawai'i astronomers.

And while they can only prove that's the case with about 30 percent of quasars, they believe it's probably true for all of them.

Every quasar has a black hole at its heart a really big one, said astronomer Hai Fu.

And it's believed that what makes a quasar glow is the radiation emitted when matter heats up as it reaches immense velocities, while being sucked into the vortex of the black hole. That hot material emits radiation in ranges all the way from X-rays to radio waves.

Astronomers believe light can't get out of a black hole, but as matter is being sucked in, radiation including light can still get out.

When astronomers view the powerful sources of pulsating light they call quasars, they may be viewing the merging of galaxies.

Fu, an astronomy graduate student, and astronomy professor Alan Stockton, in an article published in the Aug. 1 issue of the Astrophysical Journal Letters, said they looked at quasars that exhibited radiation signatures with dominant levels of hydrogen and helium.

These precursors of other elements are more common in primitive galaxies. Black holes are often found in more mature galaxies that have larger proportions of heavier elements.

"We found that the gas that is spiraling into the black hole is almost pure hydrogen and helium, whereas the stars and other material in the surrounding giant galaxy are heavily contaminated by other elements such as carbon and oxygen," Fu said.

When the astronomers saw the radiation signature of a largely hydrogen-helium quasar, against the background of a black hole's host galaxy that contains heavier elements, they theorized that they were seeing a gas from a primitive galaxy being consumed by the black hole of a mature galaxy. About 30 percent of quasars seem to display this pattern, Fu said.

And while other quasars might represent a mature galaxy's black hole munching on another mature galaxy, they have found no direct way to prove it, since the signatures of both reflect similar elemental signatures, he said.

"We believe that 100 percent of quasars are due to collisions, but we don't really have direct evidence for that," Fu said.

Fu and Stockton studied data collected from the Hubble Space Telescope, and images from the University of Hawai'i 88-inch Telescope and the Canada-France-Hawai'i Telescope on Mauna Kea.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.