This disturbed spiral galaxy, also known as NGC 4651 and the Umbrella Galaxy, is located 75 million light years away in the constellation of Coma Berenices at a declination of +16 degrees. It is a visual magnitude 11 galaxy whose main disk spans 4 arc-minutes in our apparent view. This corresponds to a diameter of 90,000 light years. The faint stellar streams extend for over 200,000 light years, both left and right of the disk.
The tidal star streams are believed to be trails of stars gravitationally stripped from a smaller satellite galaxy. The smaller galaxy was eventually torn apart in repeated encounters as it swept back and forth on eccentric orbits past the larger galaxy. I have been puzzled why the tidal stream is in a fairly straight line on the left side.
This link includes a mouseover which superimposes a simulation of the satellite galaxy's path as it was absorbed into the main galaxy. The straight line appears to be due to our view of the plane of the smaller galaxy's path.
Although the star streams attract most of the attention here, the galaxy disk is not far behind in its beauty. A small yellow core is surrounded by short arm segments with blue star-forming regions. The arms are discontinuous and hard to trace, likely because of disturbance from the merged galaxy. Numerous blue star clouds are seen in the outer arms along with hints of pink HII regions.
This galaxy is the original and classic Umbrella Galaxy, but there are a few other galaxies out there which have this "umbrella" star stream characteristic (although not quite as nice as this one). I have included them in my
Astrobin Umbrella Galaxy Collection.
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