Anne’s Picture of the Day

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October 12, 2012

The Umbrella Galaxy, a spiral galaxy in Coma Berenices

Image Credit: R Jay Gabany (Blackbird Observatory)

The Umbrella Galaxy (designated NGC 4651 and Arp 189) is a spiral galaxy located on the outskirt of the Virgo Cluster of galaxies of which it is a member, at a distance not well determined that ranges from 35 to 72 million light-years in the constellation of Coma Berenices. It is receding from us at 788 kilometers per second.

About 50 thousand light-years across, this galaxy has a faint umbrella-shaped structure (right) that seems to extend some 50 thousand light-years farther, beyond the bright galactic disk. It is known as the Umbrella Galaxy due to this umbrella-shaped structure.

The Umbrella Galaxy has an active galaxy nucleus (AGN) and a fine spiral structure. Unlike most spiral galaxies of the Virgo Cluster, NGC 4651 is rich in neutral hydrogen, also extending beyond the optical disk, and its star formation is the typical for a galaxy of its type.

The giant cosmic umbrella is composed of stellar streams, being the remnants of a much smaller galaxy that has been torn apart by NGC 4651′s tidal forces, something that explains why the Umbrella Galaxy has been included on Halton Arp’s Atlas of Peculiar Galaxies as Arp 189 –as a galaxy with filaments. (Arp’s Atlas of Peculiar Galaxies is a catalog of 338 peculiar galaxies produced by Halton Arp in 1966.)

Studies using radiotelescopes of the distribution of its neutral hydrogen show distortions on NGC 4651′s outer regions and a gas clump associated with a dwarf galaxy that may have born in the event that produced the mentioned stellar streams.

The galaxy can be seen with amateur telescopes.

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