Hydrogen in M33.

Gorgeous spiral galaxy M33 seems to have more than its fair share of hydrogen. Its inner 30,000 light-years are shown here in an image processed to fully reveal the reddish glow of ionized hydrogen regions ( HII regions ) sprawling along loose spiral arms that wind toward the galaxy's core. Historically of great interest to astronomers, M33's giant HII regions are some of the largest known stellar nurseries - sites of the formation of short-lived but very massive stars . Intense ultraviolet radiation from the luminous, massive stars ionizes the surrounding hydrogen gas and ultimately produces the characteristic red glow. A prominent member of the local group of galaxies , M33 is also known as the Triangulum Galaxy and lies about 3 million light-years distant.