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Green pea galaxy could illuminate early cosmic evolution

Cosmic reionization was key in creating the universe we know today, and we may have "green pea" galaxies to thank.
By Brooks Hays   |   Jan. 14, 2016 at 12:19 PM

CHARLOTTESVILLE, Va., Jan. 14 (UPI) -- Researchers think a class of nearby dwarf galaxies dubbed "green pea" galaxies -- named for their small, round, green appearance -- hold clues to the evolution of the early universe.

The early universe was twice hot enough to ionize matter. The second time, called cosmic reionization, followed a period of cooling that allowed the universe's material to begin to coalesce into gas and dust clouds, collapsing to form the first stars and galaxies.

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But prior to the reionization, the universe was mostly opaque -- scattered protons and free electrons absorbing most of the universe's light. When the cosmos reheated, a process known as recombination saw electrons and protons come together to form neutral hydrogen atoms. Light was now free to travel through a much more transparent universe.

Cosmic reionization was key in creating the universe we know today, but scientists haven't been able to confirm what exactly set it in motion.

A number of astronomers have suggested early forming dwarf galaxies could be responsible for the reheating and reionization. To test that theory, a team of astronomers decided to take a closer look for galaxies "ejecting" sufficient ionizing radiation.

Green pea galaxies were discovered in 2007, and astronomers thought they might fit the bill, so they scanned the Sloan Digital Sky Survey, a massive database of galaxies, for potential matches. They identified 5,000 and then picked five to study in detail.

One of the galaxies was found to be spitting a significant amount of ionizing photons into intergalactic space. The galaxy was J0925+1403, located 3 billion light-years from Earth and with an impressive 8 percent ejection rate.

"This galaxy appears to be an excellent local analog of the numerous dwarf galaxies thought to be responsible for the reionization of the early universe," lead researcher Trinh Thuan, an astronomer at the University of Virginia, said in a press release. "The finding is significant because it gives us a good place to look for probing the reionization phenomenon, which took place early in the formation of the universe that became the universe we have today."

Thuan and his colleagues shared their early observations of the galaxy in a paper, newly published in the journal Nature.

"As we make additional observations using Hubble, we expect to gain a much better understanding of the way photons are ejected from this type of galaxy, and the specific galaxy types driving cosmic reionization," Trinh said.

Researchers believe their findings will lay the groundwork for even more illuminating observations in the near future -- using the James Webb Space Telescope, which is scheduled to launch in 2018.

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