It may be a “train wreck,” in the words of UC Berkeley astronomer Dan Weisz, but it’s a beautiful train wreck.
A mosaic image of the entire Andromeda galaxy (Messier 31, or M31), 2.5 million light years away but six times larger than the moon in the night sky, was released today (Jan. 16) by the Space Telescope Science Institute in Maryland. The galaxy’s brilliant yellow center is surrounded by an ethereal blue luminescence, the stars like grains of sand on a beach.
What it reveals, Weisz says, is that the galaxy has collided with another galaxy over the past 5 billion years, leaving behind trails of star formation that astronomers can use to trace these collisions into the past. Weisz was a co-principal investigator on the first part of the Andromeda survey, the Panchromatic Hubble Andromeda Treasury (PHAT) program, which produced a hi-resolution image of the galaxy’s northern half in 2015. He is a co-investigator on the second and final phase, the Panchromatic Hubble Andromeda Southern Treasury (PHAST).