Re: Yahoo! News Story - Collisions Fuel Black Hole Feeding Frenzies - Yahoo! New
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> Collisions Fuel Black Hole Feeding Frenzies - Yahoo! News
Collisions Fuel Black Hole Feeding Frenzies
SPACE.com Mon Jun 23, 4:15 PM ET
Black hole feeding frenzies are fueled by galactic collisions,
suggests a new study that confirms astronomers' suspicions.
Astronomers have had their eyes on a certain class of galaxies that
appear to contain central black holes that gorge on gas and dust. So
far, scientists have been unsure what triggers these giant meals, but
new radio observations may help explain how they work.
Seyfert galaxies are a type of galaxy known as Active Galactic Nuclei
(AGN), thought to host supermassive black holes in their centers.
Seyferts are slightly tamer versions of the extremely luminous AGN
called quasars and blazars.
Scientists guessed that recent interactions with neighboring galaxies
might have stirred up Seyferts' gas and dust and propelled it toward
their giant black holes. But when optical telescopes observe Seyferts
in light visible to the human eye, the Seyferts show no sign of close
encounters with other galaxies.
Now astronomers have used the Very Large Array (VLA) telescope to
photograph these objects in radio light, and found that the majority
of Seyferts do indeed seem to have recently collided with a neighbor.
For comparison, the researchers observed non-Seyfert galaxies and
found that very few showed signs of an interaction.
"This comparison clearly shows a connection between close galactic
encounters and the black-hole-powered activity in the cores," said
Ya-Wen Tang, who began this work at the Institute of Astronomy &
Astrophysics, Academia Sinica (ASIAA), in Taiwan and now is a graduate
student at the National Taiwan University. "This is the best evidence
yet for the fueling of Seyfert galaxies. Other mechanisms have been
proposed, but they have shown little if any difference between
Seyferts and inactive galaxies."
The VLA telescope was able to study the galaxies' hydrogen gas by
observing the radio waves emitted by hydrogen atoms. The hydrogen gas
in many Seyferts left a clear signal of being disturbed by a collision
with another galaxy.
"Our results show that images of the hydrogen gas are a powerful tool
for revealing otherwise-invisible gravitational interactions among
galaxies," said Jeremy Lim, also of ASIAA. "This is a welcome advance
in our understanding of these objects, made possible by the best and
most extensive survey ever made of hydrogen in Seyferts."
The new study helps scientists better understand these violent
systems, where gas and dust swirl around dense black holes that
eventually gobble up the incoming material.
"The VLA lifted the veil on what's really happening with these
galaxies," said Cheng-Yu Kuo, a graduate student at the University of
Virginia. "Looking at the gas in these galaxies clearly showed that
they are snacking on their neighbors. This is a dramatic contrast with
their appearance in visible starlight."