Astronomers have confirmed the existence of a 'bridge' of hydrogen gas connecting two of our neighboring galaxies, indicating that they may once have brushed together.
Recent studies with the National Science Foundation's Green Bank Telescope (GBT) back up tthe disputed discovery in 2004 of hydrogen streaming between the giant Andromeda Galaxy, also known as M31, and the Triangulum Galaxy, or M33.
The two galaxies are about 2.6 and three million light-years from Earth respectively.
"The properties of this gas indicate that these two galaxies may have passed close together in the distant past," says Jay Lockman, of the National Radio Astronomy Observatory (NRAO). "Studying what may be a gaseous link between the two can give us a new key to understanding the evolution of both galaxies."
The 'bridge' between the galaxies was originaly discovered by astronomers using the Westerbork Synthesis Radio Telescope in the Netherlands - but was questioned on technical grounds.
However, detailed studies with the highly-sensitive GBT have confirmed its existence, and show six dense clumps of gas in the stream.
The clumps have roughly the same relative velocity with respect to Earth as the two galaxies, strengthening the argument that they are part of a bridge between the two.
When galaxies pass close to each other, one result is 'tidal tails' of gas 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," sys Spencer Wolfe, of West Virginia University.
"The encounter had to be long ago, because neither galaxy shows evidence of disruption today."