Leo Triplett (M 65, M 66, NGC 3628)

The Leo Triplet consists of the three spiral galaxies M66, M65, and NGC 3628. It is also known as the M66 group and is located 36 million light-years away.

The galaxy NGC 3628 is perhaps one of the most interesting bright galaxies. One striking feature associated with this galaxy is a long tidal star tail approximately 300,000 light-years long. NGC 3628 itself is about 160,000 light-years long. The tail is believed to consist of stars that were torn off the galaxy either when a small dwarf galaxy passed by or during a close encounter of NGC 3628 and M66.

The mass of the tail is about 15% of that of the large galaxy, and its surface brightness is about 26.5 mag/arcsec^2. The stars in the tail have an age of several hundred million years, corresponding to a close encounter of NGC 3628 and M66 about 800 million years ago.

In 2014, a tidal dwarf galaxy was discovered at the end of the tail.