Tiny Galaxy Spotted Halfway Across the Universe

Keck image of SDSSJ0737+3216, showing the bright elliptical lens galaxy and its Einstein ring. The sub-panels show a zoomed-in view, before and after subtraction of the bright foreground galaxy to leave the tiny background object ready for analysis. Credit: UCSB

Astronomers have spotted and weighed a tiny galaxy located 6 billion light-years away, or nearly halfway across the universe.

Dubbed SDSSJ0737+3216, the just discovered galaxy is 100 times lighter than our own Milky Way and is the smallest galaxy ever identified at that distance. It is about half the size and approximately one-tenth the "weight" of typical small galaxies found closer to Earth.

The galactic lightweight was found using NASA's Hubble Space Telescope and the W.M. Keck Observatory in Hawaii. It was made visible by a phenomenon called gravity lensing, whereby light from a distant source is warped by the gravitational field of another massive object located directly in front of it.

In this case, the small galaxy's light was distorted as it passed within the vicinity of a massive foreground galaxy. The warped light formed an arc, and when seen from Earth, forms a bull's-eye pattern called an "Einstein ring" around the foreground galaxy.

The new galaxy, discovered by Phil Marshall of the University of California, Santa Barbara and his colleagues, will be detailed in the Dec. 20 issue of Astrophysical Journal.