NGC 3646 - Ring Galaxy
NGC 3646 is found at a distance of 185 million light years in the constellation Leo. It has an apparent magnitude of 10.8mag and a size of
3.9'x2.2' arcminutes and was first discovered by F.W. Herschel on a cold February night in 1784.
Ring galaxies like NGC 3646 are very rare in the universe because they are only formed when two galaxies interact with each other. In the
case of NGC 3646, it was hit near the center by another galaxy, as if hitting a bull's-eye with an arrow - figuratively speaking, a frontal
collision. With a diameter of 210,000 light years, the galaxy is much larger than our Milky Way. The absolute magnitude is an impressive
M= -23.0mag, which corresponds to a luminosity of 130 billion suns.
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The ring cannot be seen entirely even with 20" aperture, just the part on the northwestern side. This reminds more of a spiral arm and is visible
quite clearly. At the southern end of the arm you can see a brighter thickening. At a high magnification you can also detect a very faint star that
flashes out every now and then. The remaining part of the ring is too faint and therefore blends with the halo of the galaxy, even though I had
the impression to see an arc-shaped structure here from time to time.
In the center of the galaxy there is a stellar nucleus, which probably comes from a very dense central region.
