Quasars Shed Light on Swirling Clouds Around Distant Galaxies

Astronomers have uncovered new information about the swirling clouds of gas that form stars and galaxies. By studying brilliant quasars, the scientists have found that the clouds can shift and change much more quickly than previously thought.

Quasars are actually an abbreviation of the phrase "quasi-stellar radio source." Appearing to be star-like in the sky, they're actually the intensely powerful centers of distant, active galaxies, powered by a huge disk of particles surrounding a supermassive black hole.

"Quasars, while very interesting, are merely tools in this study to help us actually find and study what we're really interested in, which is the invisible gas that surrounds galaxies," said Robert Brunner, one of the researchers, in a news release. "That gas gets turned into stars, and stars expel gas back out of the galaxy. One of the things we have a hard time understanding is, how is that gas involved in the formation and evolution of a galaxy? So we use quasars as big searchlights."

In order to learn more about this gas, the researchers looked at data collected from quasar light that traveled through the gas clouds in galaxies between Earth and the quasars. By measuring how much of that light was absorbed by the clouds, the researchers could tell a lot about the makeup of the clouds themselves.

Yet what makes this effort more unusual than previous attempts is that the scientists looked at the quasar light not once, but at two different times. In the span of just five years, the researchers saw measurable shifts in a small but substantial number of the giant gas clouds mapped.

"The new aspect of this work is the gas is very distant from the quasar," said Troy Hacker, one of the researchers, in a news release. "It has no physical interaction with the quasar itself. Something within a galaxy, unassociated with the quasar, is causing the observed change."

An explanation for the change could be that the gas clouds are much smaller than current theories believe. This, in turn, may mean that small structures in other galaxies may be more prevalent than originally thought, which could pave the way for future findings.

"The gas around other galaxies has different types of structures and shapes," said Brunner in a news release. "The data are telling us that the dynamics are more complex than previously thought, and you can use that to get a limit on the size and motions of these clouds. Now we can start thinking about tying all these things together--what is the chemistry in these clouds, and how are they tied to the stars in these galaxies?"

The findings are published in the journal Monthly Notices of the Royal Astronomical Society.