"We might be witnessing the final stages of the formation process of our galaxy, " says W. Butler Burton, radio astronomer. A giant cloud of hydrogen gas, clocked at more than 150 miles per second per second, is closing in very fast on the Milky Way, likely setting off a huge burst of star formation. At its current speed, the cloud will collide with interstellar gas in the Milky Way's disk in less than 40 million years, condensing into tens of thousands of bright, massive stars that will explode as supernovas within a couple of million years.
Many clouds of hydrogen surround the Milky Way. But astronomers didn't start spotting them until a half-century ago--after the advent of radio telescopes, which are able to detect cold, neutral hydrogen gas. The early observations were not accurate enough to determine the clouds' distances, masses, or directions of motion.
The hydrogen cloud, named Smith's Cloud after Dutch astronomy student Gail Smith, who discovered it in 1963. Curious about the cloud's elongated shape, a team of astronomers led Lockman o, took tens of thousands of radio brightness measurements. The data reveal that the cloud is just 8000 light-years away from the Milky Way's central plane, making it the closest one known. Its comet-like shape is apparently due to the tidal effects of the Milky Way.
The Daily Galaxy via nrao.edu