Messier 79

Messier 79 (also cataloged as M79 or NGC 1904) is a globular cluster located in the southern constellation Lepus. French astronomer Pierre Méchain first spotted it in 1780. The cluster lies roughly 42,000 light-years from Earth and about 60,000 light-years from the Milky Way’s center.

Like Messier 54—the other extragalactic globular on Messier’s list—M79 is thought to have originated outside the Milky Way. It likely belongs to the suspected Canis Major Dwarf Galaxy, which is currently passing very close to our own galaxy. However, this idea remains debated, as astronomers still disagree on whether the Canis Major Dwarf Galaxy itself is a real structure. Some evidence also suggests M79 might be part of the Gaia Sausage. The cluster is slowly being pulled apart by the Milky Way’s tidal forces, leaving behind a long tidal tail.

A color-magnitude diagram of M79, created from near-infrared images in the J and K bands, shows J-band magnitude on the vertical axis and J–K color on the horizontal axis. This diagram was produced quickly using specialized software designed for crowded-field photometry. It reveals that most of the cluster’s bright stars are red giants, forming an elongated red giant branch. Some stars in the diagram—especially those extending from the red giant branch toward the upper left—are actually foreground stars not part of the cluster.

Three regions of the Hertzsprung–Russell diagram appear here: the low-mass end of the main sequence, the complete red giant branch, and the horizontal branch. Compared to optical bands, the infrared bands make the lower main sequence shallower and the horizontal branch steeper (the blue end is fainter, the red end brighter).