New Galaxy Discovered Orbiting Milky Way

A diffuse collection of stars southwest of the bowl of the Big Dipper, this galaxy lies about 330,000 light years away, twice as far as the Large Magellanic Cloud, the Milky Way’s brightest satellite galaxy. It is a dwarf spheroidal, a small gas-poor galaxy with a small number of stars that are widely separated from one another. Half of the light of this galaxy comes from a region 1,600 light-years across. This is typical of dwarf spheroidals.

Willman’s team says that the new galaxy resembles another Milky Way satellite: the Sextans dwarf spheroidal. Both of these galaxies are ancient and have few elements heavier than hydrogen and helium.

A big difference between the two dwarf spheroidal galaxies, though, is that the newly discovered galaxy is much less luminous. It has only about one tenth as many stars as the Sextans dwarf. Willman’s team estimate that the new galaxy emits only 1/350,000 of the light given off by the Milky Way. Some stars in the Milky Way, for example, Deneb in Cygnus, emit more light than all the stars in the new galaxy put together. The new Ursa Major dwarf galaxy is the least luminous galaxy ever seen.