Observations by the National Science Foundation's Green Bank Telescope in West Virginia confirm a disputed 2004 discovery of a hydrogen gas "bridge" streaming between the giant Andromeda Galaxy, also known as M31, and the Triangulum Galaxy, or M33, the National Radio Astronomy Observatory reported Monday.
"The properties of this gas indicate that these two galaxies may have passed close together in the distant past," observatory researcher Jay Lockman said.
"Studying what may be a gaseous link between the two can give us a new key to understanding the evolution of both galaxies."
The two galaxies are members of the so-called Local Group of galaxies that includes our own Milky Way and about 30 others.
When galaxies pass close to each other, one result is "tidal tails" of gas pulled into intergalactic space from the galaxies as lengthy streams, the researchers said.
"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. "The encounter had to be long ago, because neither galaxy shows evidence of disruption today."