The new galaxy is about 2 light-years farther away than previous record-holder, a gamma-ray burst that faded within a few hours of its peak brightness, and 200 million light-years farther than the next most distant galaxy.

“We are approaching the limits of the observable universe with this observation,” said astronomer Michele Trenti of the University of Colorado, who was not involved in the new work. “It is quite a good improvement.”

The finding, published in the Oct. 21 Nature, could also give insight into how young stars helped make the universe transparent.

The new distance champion, deemed UDFy-38135539, was first spotted in late 2009 in a Hubble Space Telescope image called the Ultra Deep Field. The image captures 10,000 galaxies in the universe’s earliest epochs, several of which were good candidates for the most distant galaxy.

Because light takes time to travel across the universe, telescopes see these galaxies as they appeared billions of years ago. And because the universe is expanding, distant galaxies appear to be rapidly moving away from us. As the galaxies flee, the wavelength of the light they emit stretches out, or redshifts, similar to how an ambulance siren’s howl drops in pitch as it drives away.

Matt Lehnert of the Paris Observatory and colleagues picked the reddest galaxy in the Ultra Deep Field, then took 16 hours of follow-up observations with the SINFONI spectrograph on the Very Large Telescope in Chile.

The team searched for the specific wavelength of light emitted when hydrogen, the most abundant element in the universe, relaxes from an excited energy state. Based on the amount of stretching this light experienced on its journey from the distant galaxy to the telescope, astronomers calculated that the galaxy is 13.1 billion light-years away, making it at least 2 light-years farther than the next-most distant object ever found. The galaxy probably formed within 600 million years of the Big Bang.

Detecting this light at all was a surprising feat, Trenti said. “Most astronomers in the community think spectroscopic confirmation would have been very, very difficult. They were reluctant to try to invest a significant amount of telescope time to get the spectrum,” he said. “Lehnert and colleagues went ahead and really showed that this can be done now, we don’t have to wait for the next generation of more powerful telescopes.”

A 2-light-year gain may not sound like much on the scale of the entire universe, Trenti added, but it’s like breaking the world record in the 100 meter dash. “You run a few hundredths of a second faster, but that is a big deal,” he said.

But the new galaxy is more than just “a trophy on the wall,” Lehnert said. UDFy-38135539 is the first galaxy observed that formed during the “epoch of reionization,” when radiation from infant stars split hydrogen atoms that fogged up the early universe into protons and electrons. Hydrogen absorbs light at most wavelengths, so without early stars, even nearby galaxies would be completely invisible to us.

Reionization began around 600 million years after the Big Bang and wrapped up a few hundred million years later, “which, for the universe, is relatively a blink of an eye,” Lehnert said. “But we don’t know how it happened.” The new most-distant galaxy “basically helps to give us insight into the first galaxies, the galaxies that really were responsible for reionization.”

Astronomers know one thing already: The new galaxy is not alone. The galaxy’s young stars blew a transparent bubble of ions around it, which must be big enough to allow astronomers to see the galaxy from Earth. But observations suggest that the galaxy corrals only about 1 billion stars, making it at least 100 times smaller than the Milky Way — too small to blow such a big ionic bubble by itself.

“It must have had friends around it to help it,” Lehnert said. “We have no idea what these friends are like… but this tells us they must be there, and we’re feeling their presence.”

The most likely candidates for these helpers are fainter galaxies, but they could be exotic objects like miniature black holes or decaying particles, Lehnert says.

Image: NASA/ESA/G. Illingworth/HUDF09 Team

See Also:

• Soggy Universe: Astronomers Find Most Distant Water Yet
• Hubble Finds Farthest, Oldest Galaxies Ever Seen
• Hubble Goes Deep, Finds Farthest Galaxies Yet
• Early Galaxies Formed Stars Fast Because They Had More Gas

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Authors: Lisa Grossman

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