Hickson Compact Group 59, a group of galaxies in Leo

Hickson Compact Group 59, a group of galaxies in Leo

Hickson Compact Group (HCG) 59 consists of a variety of galaxies, about 180 million light-years away in the constellation Leo. There are three main galaxies, of which two are star-forming while the other one is quiescent.

The main galaxies are two large spirals, one face-on with smooth arms and delicate dust tendrils, and one highly inclined, as well as a strangely disorderly galaxy featuring clumps of blue young stars. In this image we can also see many apparently smaller, probably more distant, galaxies visible in the background.

Hickson Compact Groups are small, relatively isolated clusters of galaxies listed in a catalogue published in 1982 by the British-born Canadian astronomer Paul Hickson (1950–). A typical Hickson Compact Group contains four to five closely spaced members, up to half of which may be interacting or even merging. (The most famous groups on Hickson’s list of 100 objects are Stephan’s Quintet and Seyfert’s Sextet.)

HCGs most likely form as subsystems within looser associations and evolve by gravitational processes. Strong galaxy interactions result and merging is expected to lead to the ultimate demise of the group. Possibly compact galaxy groups and interacting galaxies play a significant role in galaxy evolution.

Hickson Compact Groups display many peculiarities, often emitting in the radio and infrared and featuring active star-forming regions. In addition their galaxies frequently contain Active Galactic Nuclei (AGN) powered by supermassive black holes. HCGs contain large quantities of diffuse gas and are dynamically dominated by dark matter.

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