Barnard's Galaxy (NGC 6822) is a dwarf irregular galaxy in the constellation Sagittarius. About 1.6 million light-years away, it is one of the closer galaxies to the Milky Way, and a member of the Local Group. It is similar in structure and composition to the Small Magellanic Cloud.
NGC 6822 was discovered by E.E. Barnard in 1884 with a 6-inch refractor. In 1925, Edwin Hubble identified eleven Cepheid variables in NGC 6822. Utilizing the Cepheid period-luminosity relationship, he determined a distance of more than 700,000 light-years, and recognized NGC 6822 as a member of the Local Group. NGC 6822 was the first galaxy beyond the Magellanic Clouds to have its distance accurately determined.
From our vantage point, this small galaxy appears nearly rectangular, about 16' across. Perhaps one-tenth our galaxy’s size, NGC 6822 is formally classified as a "barred irregular" galaxy.
More peculiar, however, is NGC 6822's unusually high abundance of HII regions - locales of ionized hydrogen that surround young stars. Today, there are over 150 of these regions cataloged in Barnard's Galaxy. The largest currently active star formation region in NGC 6822 is called Hubble-X. This bright, nearly circular cloud at the core of Hubble-X measures about 110 light-years across. It contains a central cluster of many thousands of young stars, less than 4 million years old. A bluish arm of loosely-grouped young stars extends outward.
In the 1920s, Hubble found three star clusters in Barnard's Galaxy that he believed were all very old objects similar to the Milky Way's globular clusters. However, images taken by the Hubble Space Telescope have shown that these clusters are of completely different ages. The stars in the cluster called Hubble VII were formed about 15 billion years ago, and are about the same age as the Universe itself. A second cluster known as Hubble-VIII contains stars about 1.8 billion years old; while a third cluster, Hubble VI, has stars that are as young as 100 million years.
It seems that, unlike the Milky Way (whose big globular clusters mostly formed in the first few billion years after the Big Bang), Barnard’s Galaxy has been generating massive, new star clusters all along.