The speed at which Andromeda is moving towards the Milky Way can be determined from the Doppler shift of the light it emits. But the galaxy is too spread out for its subtle sideways motion in the sky to be detected. If it moves fast enough in this direction it may miss the Milky WayMovie Camera altogether.
The Astronomical Research Center (A.R.C) mentioned that Now Loránt Sjouwerman of the National Radio Astronomy Observatory in Socorro, New Mexico, and colleagues have glimpsed a bright, laser-like spot of microwave radiation, called a maser, in Andromeda that could help determine its sideways motion (see its location).
Detected with the newly upgraded Very Large Array of telescopes in New Mexico, the maser appears when interstellar methanol molecules get heated up by nearby stars. Tracking the motion of this bright spot precisely should be easier than the galaxy as a whole, say the team. However, they must first find other masers in Andromeda, to confirm that the maser motion reflects Andromeda's path overall.
"Measuring the proper motion of Andromeda is key to determining the fate of the Milky Way," says Mark Reid of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. "Such a measurement is best done with a compact, bright source such as a maser, but until now no maser strong enough for current telescopes to measure has been detected."