Interacting spiral galaxies Arp 273 Spiral galaxies are
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Interacting spiral galaxies Arp 273. Spiral galaxies are rotating disk systems of stars, gas and ...

April 14, 2010
Interacting spiral galaxies Arp 273.

Spiral galaxies are rotating disk systems of stars, gas and dust. Due to their varying orientations in the sky, they may appear as face-on whirlpools, edge-on disks or as something in between. Spirals are classified based on the tightness of their arms and the size and shape of their nucleus. Those with an elongated bar-like center are called "barred spirals."

The distance of this galaxy is approximately 200 million light-years from Earth. The orientation of the image is north up, west to the left. This image was taken at the WIYN observatory using the WIYN 3.5-meter telescope, one of the best imaging telescopes in the world. The WIYN Observatory (pronounced "win") is located on Kitt Peak near Tucson, Arizona, and is owned and operated by the WIYN Consortium, which consists of the University of Wisconsin, Indiana University, Yale University and the National Optical Astronomy Observatories (NOAO).


This pair of spiral galaxies was first described in the "Catalogue of Peculiar Galaxies," compiled by Halton Arp in 1966. It is also pair number 64 in Igor Karachentsev's catalog of binary galaxies. The larger member is strongly, tidally distorted, looking almost as though one side of the galaxy has been placed under a magnifying glass. The edge-on companion, however, retains a relatively undisturbed spiral disk, but has a luminous, heavily obscured but infrared-bright, starburst nucleus. The nucleus of the large spiral, by way of a contrast, contains a low-ionization nuclear emission-line region (LINER), which is indicative of much less activity than the bright nuclear HII region of its companion. This is an interesting example of the very different responses that different galaxies can have to interaction with their companions: the large galaxy has a shredded disk but essentially nothing in its nucleus, while the small galaxy has an undisturbed disk but a very active nucleus.

This two-minute exposure was taken on the night of September 26, 1994.

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