Caltech scientists detect farthest galaxy

The researchers were able to date the galaxy by measuring its redshift -- the Doppler effect, but with light instead of sound.
By Brooks Hays  |  Sept. 4, 2015 at 5:37 PM
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PASADENA, Calif., Sept. 4 (UPI) -- Researchers at Caltech have spotted a faint galaxy which they believe to be the farthest ever observed. The discovery challenges the timeline and explanation of the evolution of the early universe.

The cosmos is 13.8 billion years old. EGS8p7 -- the galaxy newly discovered by a team of astronomers, with help from several telescopes -- is more than 13.2 billion years old.

Astronomers have measured a type of radiation emanating from the distant galaxy that, in theory, shouldn't be possible -- radiation including a Lyman-alpha line, the spectral signature of hot hydrogen gas. Radiation of this kind and this age should have been swallowed up and absorbed by clouds of neutral hydrogen in the early universe.

In the wake of the Big Bang, the universe was a swirling mess of primordial soup. Scattered free electrons made it impossible for light to travel through space. Eventually, the cosmos cooled and electrons paired up with protons to form clouds of neutral hydrogen gas. And about 500 million years after the birth of the universe, stars began forming, ionizing the gas and allowing radiation to travel.

The new galaxy doesn't throw this theory entirely on its head, but it does suggest cosmologists need to rethink the timing.

"If you look at the galaxies in the early universe, there is a lot of neutral hydrogen that is not transparent to this emission," Adi Zitrin, a NASA Hubble Postdoctoral Scholar in Astronomy at Caltech, explained in a press release. "We expect that most of the radiation from this galaxy would be absorbed by the hydrogen in the intervening space. Yet still we see Lyman-alpha from this galaxy."

Zitrin and colleague Richard Ellis -- a former Caltech researcher, now a professor of astrophysics at University College, London -- described the galaxy in the latest issue of the Astrophysical Journal Letters.

The researchers were able to date the galaxy by measuring its redshift -- the Doppler effect, but with light instead of sound.

"The surprising aspect about the present discovery is that we have detected this Lyman-alpha line in an apparently faint galaxy at a redshift of 8.68, corresponding to a time when the universe should be full of absorbing hydrogen clouds," Ellis said.

Zitrin and Ellis say their findings suggest ionization didn't happen uniformly. It's possible that EGS8p7 featured such large hot stars that it ionized its own large clouds of hydrogen gas, allowing its radiation to escape into the outer reaches of the universe much earlier than its peers.

"We are currently calculating more thoroughly the exact chances of finding this galaxy and seeing this emission from it, and to understand whether we need to revise the timeline of the reionization, which is one of the major key questions to answer in our understanding of the evolution of the universe," Zitrin said.

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