NGC 3621

NGC 3621 is a spiral galaxy located approximately 22 million light-years away in the constellation Hydra. It's classified as a pure-disk galaxy, notable for its lack of a central bulge, which is unusual for spiral galaxies of its size. This makes NGC 3621 a valuable object for studying the formation and evolution of spiral galaxies, especially the role of dark matter in shaping their structure.

The galaxy spans roughly 93,000 light-years in diameter and is tilted significantly with respect to our line of sight, presenting a near edge-on view. Its prominent spiral arms are filled with star-forming regions, evident in the bright blue patches caused by hot, young stars. These star-forming regions are interspersed with dark dust lanes that obscure the light from stars behind them.

NGC 3621 is relatively isolated, meaning it's not gravitationally interacting strongly with other large galaxies. This isolation contributes to its unique bulge-less morphology. Astronomers have used Cepheid variable stars within NGC 3621 to accurately measure its distance, contributing to the cosmic distance ladder used to determine the expansion rate of the universe.

The galaxy also exhibits evidence of a weak active galactic nucleus (AGN), suggesting the presence of a supermassive black hole at its center, although its activity is significantly lower than that of Seyfert galaxies or quasars. Studies have revealed that NGC 3621 harbors a complex network of gas and dust in its interstellar medium, further fueling star formation processes.