October 1, 2012
Quasar Gas Clouds: ‘Gone With The Wind’
Lee Rannals for redOrbit.com — Your Universe Online
The distant quasar gas clouds that seemed to disappear off the grid were gone with the wind, according to a study published in The Astrophysical Journal.
Astronomers Nurten Filiz Ak and Niel Brandt of Pennsylvania State University led the team to search for the missing quasar gas clouds that seemed to disappear in just a few years.
"We know that many quasars have structures of fast-moving gas caught up in 'quasar winds,' and now we know that those structures can regularly disappear from view," Filiz Ak, a graduate student at Penn State and lead author of the paper, said in a statement. "But why is this happening?"
Quasars are powered by gas falling into supermassive black holes at the center of galaxies. As the gas falls into the black hole, it heats up and gives off light.
The gravitational force from the black hole is so strong, and pulling so much gas, that the gas glows brighter than the surrounding galaxy. Not all the gas is able to find its way into the black hole; much of it escapes and is carried off by strong winds blowing out from the center for the quasar.
"These winds blow at thousands of miles per second, far faster than any winds we see on Earth," Niel Brandt, a professor at Penn State and Filiz Ak's Ph.D. advisor, said in a statement. "The winds are important because we know that they play an important role in regulating the quasar's central black hole, as well as star formation in the surrounding galaxy."
Many quasars can show evidence of these winds through measurements of the amount of light that the quasar gives off at different wavelengths.
Scientists using the Sloan Digital Sky Survey (SDSS) were able to analyze the quasar's spectra, gathering up 582 "broad absorption line" (BAL) quasar measurements.
Each of these 582 BAL quasars were reexamined between one and nine years apart. The team started searching for changes after the reexaminations and found 19 of the quasars' BALs had disappeared.
The astronomers found that the simplest possible explanation for the missing gas clouds is that they literally were "gone with the wind."
The rotation of the quasar's disk and wind carried off the clouds out of the line-of-sight between the Earth and the quasar.
Filiz Ak said that because the sample of quasars is so large, and have gathered in such a systematic manner, the team can "quantify this phenomena."
He said that about 3% of quasars show disappearing gas clouds over a three-year span, which in turn suggests that a typical quasar cloud spends about a century along our line of sight.
"Since the universe is 14 billion years old, we're used to astronomical phenomena lasting a very long time," Pat Hall of York University in Toronto, another team member, said in a statement. "It's fascinating to discover something that changes within a human lifetime."
The team said they will be continuing to analyze their sample of quasars.
"This is really exciting for me," Filiz Ak said in the statement. "I'm sitting at my desk, discovering the nature of the most powerful winds in the Universe."