Meet NGC 2903: a beautiful and bustling galaxy found approximately 20 million light-years away from Earth in the Leo constellation. It’s about as easy as it comes to classify which group it belongs to: the spiral galaxies.
Like all spiral galaxies, it has a large and bright central core, which is partially obscured by a large, dense wall of interstellar dust. Then, we see the spiral arms themselves, which contain dust as well, with high concentrations of gas present too. Of course, there isn’t enough of either to prevent starlight from seeping through. In fact, these regions continue to churn out a mind-boggling number of new stars—giving NGC 2903 an additional classification: a ‘starburst’ galaxy.
Its fantastic blue coloring comes from these energetic new stars, while shades of red come from a combination of HII regions, and much older populations of stars. To expand, HII regions are regions in which newly-formed stars energize the gas around them, ultimately stripping electrons from atoms; when the pair inevitably recombine, they glow brightly (astronomers call this ionization).
NGC 2903 is additionally known for the ring of hot spots that surround it; astronomers believe the galaxy’s ring is comprised of young globular clusters (the stars within them, which are independent of the galaxy itself, are pretty strange. The Milky Way’s globular clusters are extremely old—the oldest stars anywhere in our galaxy, even).
Despite the distance, NGC 2903 is one of the brightest galaxies visible from the northern hemisphere. Measuring in at around 80,000 light-years across, the galaxy is just a 20 percent smaller than the Milky Way.
See a larger image here.