June 13, 2012

Astronomers Say Neighboring Galaxies Had Close Encounter

Lee Rannals for redOrbit.com

According to recent studies with the National Science Foundation's Green Bank Telescope (GBT), a couple celestial neighbor galaxies may have had a close encounter with each other billions of years ago.

Astronomers confirmed a disputed 2004 discovery of hydrogen gas streaming between the giant Andromeda Galaxy and the Triangulum Galaxy with their new study.

"The properties of this gas indicate that these two galaxies may have passed close together in the distant past," Jay Lockman, of the National Radio Astronomy Observatory (NRAO), said in a press release. "Studying what may be a gaseous link between the two can give us a new key to understanding the evolution of both galaxies," he added.

The two galaxies are members of the Local Group of galaxies that includes our Milky Way galaxy, as well as about 30 others.

The hydrogen "bridge" between Andromeda and Triangulum was discovered in 2004 by astronomers using the Westerbork Synthesis Radio Telescope in the Netherlands. However, scientists questioned the discovery on technical grounds.

Now, detailed studies with the GBT confirmed the existence of the bridge, and shows six dense clumps of gas in the stream.

Observations of these clumps showed that they share about the same relative velocity with respect to Earth as the two galaxies, which lie between 2.6 and 3 million light-years away from our planet.  These observations strengthened the argument that they are part of a bridge between Andromeda and Triangulum.

Back when the galaxies passed close to each other, it created "tidal tails" of gas that pulled into intergalactic space from the galaxies as lengthy streams.

"We think it's very likely that the hydrogen gas we see between M31 and M33 is the remnant of a tidal tail that originated during a close encounter, probably billions of years ago," Spencer Wolfe, of West Virginia University, said in a press release. "The encounter had to be long ago, because neither galaxy shows evidence of disruption today."

Lockman said the gas the team studied is tenuous, and its radio emissions is faint, so much so that it is beyond reach of most radio telescopes.

"We plan to use the advanced capabilities of the GBT to continue this work and learn more about both the gas and, hopefully, the orbital histories of the two galaxies," he said in a press release.

The team worked with D.J. Pisano, of West Virginia University, and Stacy McGaigh and Edward Shaya of the University of Maryland for the study.

They will be presenting their findings at the American Astronomical Society's meeting in Anchorage, Alaska.