Colliding galaxies or a bird and egg in space?

By James Maynard , Jun 20, 2013 10:29 PM EDT

Two colliding galaxies located 326 million light years from Earth are the subjects of the newest image from the Hubble Space Telescope (HST). Together, the pair look strikingly like a bird watching over an egg.

The two galaxies are NGC 2936, which is the bird in the picture, and NGC 2937, which resembles an egg. Together, the pair is known as Arp 142. The bird-looking galaxy in the photo is often called "The Penguin" or "The Porpoise" by amateur astronomers, although other species of birds have been suggested. The pair of galaxies are located in the constellation Hydra, the Serpent.

NGC 2936 is a spiral galaxy which is being torn apart by the gravitational interaction of the nearby egg-shaped collection of stars. The original spiral structure is most visible in the head of the bird. The eye is the large central bulge of the galaxy.

The egg, NGC 2937, is an older elliptical galaxy with little in the way of new star formation. This fact is revealed in the color of the grouping. As the stars within the galaxy die, they cool, and the light they give off becomes redder and more dim.

New stars are born in areas where pressures build and the gas compresses. This ignites new stars, which in turn excite the gas around them, causing the material to shine light blue. Young, hot stars are being created in the blue areas that can be seen in the beak and belly of the bird.

As the two galaxies close, they willl begin "exchanging matter and causing havoc," NASA said. 

The reddish material making up most of the body of the bird is largely composed of dust. This material once resided inside the body of NGC 2936, but is being ripped out of the once-spiral-shaped star formation.

The picture is a combination of three different Hubble images, one taken in all bands of visible light, another in red and the third taken in infrared wavelengths. They were taken with the space telescope's Wide Field Planetary Camera 3 (WFC3).

The Arp series of objects were named after Halton Arp, an American astronomer who compiled the Atlas of Peculiar Galaxies, first published in 1966. Although Arp compiled the list based on the strange shapes of the objects listed, astronomers soon discovered that the catalog was a good resource for labeling colliding and interacting galaxies.

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