An arc of blue stars that stretches for thousands of light-years sits just above the nearby galaxy Centaurus A. Astronomers analyzing the arc have discovered that it’s the stellar remains of a tiny galaxy that was swallowed by Centaurus A only a few hundred million years ago. In the December Astronomical Journal, the scientists report that this relatively recent example of galactic cannibalism is another indication that material ripped from smaller galaxies is a key contributor to the formation of halos–the tenuous outer perimeters of galaxies.
“This adds a nice example in the local universe to the growing evidence that galactic halos are built up from the accretion of dwarf satellite galaxies,” says study coauthor Eric Peng of the Johns Hopkins University in Baltimore. Halos are intriguing, he adds, because their ancient stellar denizens provide data about galaxies as they were when they were forming billions of years ago.
