Tiny galaxy packs a wallop.

Big things sometimes come in small packages. That is especially true of the dwarf galaxy NGC 2366, which has a diameter one-seventh that of the Milky Way yet sports a star-forming region 10 times brighter and 10 times bigger than the largest in our galaxy.

Using the Hubble Space Telescope to take images and spectra of this mammoth stellar nursery, Laurent Drissen and his colleagues at Laval University in St. Foy, Quebec, found both a puzzle and a surprise.

Astronomers already knew that hydrogen gas in this nursery moves at more than 1,000 kilometers per second, but they didn't know what powers the gas.

Drissen's team speculated that the winds blown either by bright, hot stars known as Wolf-Rayet stars or by old stars called red supergiants could have pumped up the gas. The shock wave generated when massive stars explode as supernovas might also have contributed.

However, the Hubble images, which for the first time reveal individual stars in this crowded region, show no red supergiants and only one Wolf-Rayet star.

The data also indicate that the region is only a few million years old, too young for stars to have become supernovas. Drissen now believes that winds from young, massive stars might power the gas.

The images also provide an unexpected bonus. Comparing them to older, ground-based pictures, the researchers found a rare type of star called a luminous blue variable (LBV). This immense body, 30 to 60 times the mass of the sun, is in an explosive phase. Only four other LBV eruptions have ever been recorded, and the new eruption is the first for which astronomers have obtained spectra. The Hubble observations reveal that the star has grown 40 times brighter in just 3 years, reports Drissen's team in a December Astrophysical Journal Letters.