Messier 65, NGC 3623

Messier 65 (also catalogued as NGC 3623) is a spiral galaxy in the constellation Leo. M 65, M 66, and NGC 3628 comprise the famous Leo Triplet, a small group of galaxies.

M 65 was discovered, along with M 66, by Charles Messier in 1780, who described it as a "very faint nebula without stars." However, Admiral Smyth accidentally attributed their discovery to Pierre Mechain in his popular 19th century astronomical work, A Cycle of Celestial Objects. This error was picked up in many other sources by a variety of authors.

Halton Arp includes M 65 in his Catalogue of Peculiar Galaxies as no. 317, which denotes as the Leo Triplet.

Observing Messier 65

The galaxies Messier 65 and 66 are an easy pair for 10x and higher binoculars. With a visual magnitude of 9.3, and apparent dimensions of 8' x 1.5', M 65 is just slightly the smaller and fainter of the pair. M 65 is a highly inclined spiral galaxy, tilted about 14° from edge-on to our line of sight. A prominent dust lane, visible through moderate-sized telescopes, extends across the side of its disk facing toward us.

M 65 and 66, along with NGC 3628 to the north, are the core of the M 66 subgroup of the Leo I Galaxy Group. Other members of this group include NGC 3489, 3593, 3596, and 3666. Although it is close to and thus under the gravitational influence of its neighbors, M 65 looks like a very "normal" type Sa spiral galaxy. It has a prominent central lens and tightly wound spiral arms, plus a prominent dust lane marking the facing edge. Near the lane, some knots are visible, which may be associated with star forming regions. The dust may hide regions of star formation usually associated with such features in spiral galaxies.

Physical Properties

M 65 is located about 35 million light-years away; its diameter is over 80,000 light years. M 65 has an absolute magnitude of -20.6, corresponding to a luminosity of 15 billion suns. This galaxy's core is low in gas and dust, and shows little star formation, although there has been some relatively recently in the arms. Though there is a radio source, offset from the core by about 2', whose identity is uncertain.

M 65's disk appears slightly warped, and its relatively recent burst of star formation also suggests an external disturbance. The two other galaxies in the Leo Triplet may have interacted with it about 800 million years ago. M 65 may also have a central bar - a feature which is suggestive of tidal disruption - though it is difficult to tell because the galaxy is seen from such an oblique angle.