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GROWING GALAXYThis composite, false-color image is of a giant blob of glowing gas, known as a the Lyman-alpha blob, hails from a time when the universe was only 800 million years old, or 6 percent of its current age. The blob, which also contains the stellar equivalent of 40 billion suns, may be the earliest snapshot of a galaxy growing by gobbling up gas. The white bar indicates a distance of 10,000 light-years.M. Ouchi et al., Astrophysical Journal

Quick, Marge, call the Cosmic Enquirer! Astronomers have discovered a monster blob lurking at the edge of the universe. The blob may be the earliest known galaxy to be caught in the act of its first feeding frenzy.

The giant parcel of gas and stars stretches for 55,000 light-years, a little more than half the diameter of the Milky Way’s disk today. Yet this newfound object hails from a time when the universe was only 6 percent its current age.

Masami Ouchi of the Observatories of the Carnegie Institution for Science in Pasadena, Calif., and his colleagues first recorded light from the blob, along with 206 other remote galaxy candidates, with the infrared Subaru Telescope on Hawaii’s Mauna Kea. Spectra taken at the Keck Observatory on Mauna Kea and at the Magellan Telescope near La Serena, Chile, confirmed that the blob resides 12.9 billion light-years from Earth, making it the fourth most distant object known in the cosmos. Because peering deep into space is the same as looking far back in time, the body’s distance reveals that it dates from just 800 million years after the Big Bang.

This kind of body, dubbed a Lyman-alpha blob for the type of hydrogen emission it radiates, has never before been seen so early in the universe. In addition, infrared observations reveal that the new blob contains a stellar mass equivalent of about 40 billion suns, Ouchi and his colleagues report online (lanl.arxiv.org/abs/0807.4174) and in an upcoming Astrophysical Journal.

Because of the object’s remote distance, the researchers say they can’t be sure if the youthful, glowing object is gas heated by a supermassive black hole at the center of a galaxy, a huge filament of gas pulled toward the center of a single fledgling galaxy or a sign of the merger of two large galaxies.

But in several recent articles, theorists suggest Lyman-alpha blobs that formed when the universe was young are filaments of cold gas that fall into — and enlarge — a massive galaxy in the early universe. Simulations have shown that massive galaxies early in the universe grow bigger by snaring streams of cold intergalactic gas. In an article recently posted online, Avi Loeb and Mark Dijkstra of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., show that these cold gas filaments are likely to appear as Lyman-alpha blobs, just like the one found by Ouchi’s team (lanl.arxiv.org/abs/0902.2999).

“In our model, such a detection implies the formation of a massive galaxy” early in the history of the cosmos, Loeb says.

Recent work by Avishai Dekel of the Hebrew University in Jerusalem and his colleagues comes to a similar conclusion online (lanl.arxiv.org/abs/0901.2458) and in the Jan. 22 Nature.

As the gas streams into the center of a galaxy early in the universe, it gains gravitational energy, which heats the gas and causes it to emit Lyman-alpha radiation, Dekel says.

According to the standard model of galaxy formation, in which visible galaxies coalesce within a halo of invisible material called cold dark matter, galaxies start out small and grow bigger over time. But the model does allow a galaxy as large and massive as the object discovered with Subaru, Ouchi and his colleagues note, if the starlit body resides within an extremely massive dark matter halo, weighing the equivalent of about a trillion suns.

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