M31

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Image credit: Allen Telescope Array/UC Berkeley

Familiar optical of M31, Andromeda Galaxy.

The first image taken by the 42-antenna Allen Telescope Array depicts the atomic hydrogen in the Andromeda Galaxy (Messier 31 or M31), the nearest large spiral galaxy to the Milky Way. Unlike all other radio telescopes, the ATA can image large objects like M31 - its diameter is about five times the diameter of the full moon - all at once instead of piecemeal. The telescope's wide field of view makes it ideal for mapping the heavens in search of new radio sources."

The colors, from blue to white, represent the intensity of the radio emissions and thus the density of hydrogen. Because atomic hydrogen is the stuff from which stars are made, the large "hole" in the center of Andromeda indicates that the galaxy is near the end of its star formation history. In the background are radio galaxies powered by massive black holes that are billions of light years away from Earth.

M33

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Image credit: Allen Telescope Array/UC Berkeley

Optical image of M33, Pinwheel Galaxy.
Image credit: T.A.Rector (NRAO/AUI/NSF and NOAO/AURA/NSF) and M.Hanna (NOAO/AURA/NSF)

One of the first images taken by the 42-antenna Allen Telescope Array shows the atomic hydrogen in the Pinwheel Galaxy (M33), situated in the constellation Triangulum. Unlike M31, the Pinwheel Galaxy shows no hole at the center and an almost constant distribution of gas nearly to its outer radius. The Pinwheel's nearest neighbor, the Andromeda Galaxy, is large enough to generate tides in the galaxy, which blow out faint puffs of hydrogen seen at the top and bottom of the image.

The ATA's large field of view is 17 times larger than that of the Very Large Array in New Mexico, making the ATA ideal for surveys, both for radio astronomy and SETI.