Dwarf green pea galaxy might be responsible for heating up the universe about 13 billion years ago.
Scientists have probably found the answer to a longstanding troubling question.
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Several hundred thousand years after the Big Bang, the universe was very hot. It cooled down gradually as it expanded. Then, gas clouds of hydrogen and helium were formed and were later collapsed to create stars and galaxies.
About one billion years after the Big Bang, another important transformation took place. The universe again heated and hydrogen became ionized similar to what happened right after the Big Bang. Scientists called the phase "cosmic re-ionization.” But how could it happen again? The reason is still unknown.
But now researchers claim that a small, greenish color galaxy is probably responsible for the transformation.
The green pea galaxy, J0925+1403, is located three billion light years away from the Earth. The galaxy was discovered using an ultraviolet spectrometer aboard the Hubble Space Telescope and is ejecting a large number of ionized photons into the space. Scientists believe that those photons might have something to do with universe’s re-ionization.
"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," said Trinh Thuan, an astronomer from University of Virginia. "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."
Green pea galaxies are a rare class of galaxies discovered in 2007. They emit green light and have a round and compact shape like a pea. It is believed that stellar explosions frequently occur in those green galaxies which lead to ejecting ionizing photon.
Scientists have long suspected that galaxies were responsible for cosmic ionization. But, for ionization to occur, galaxies must eject these photons into intergalactic medium or the space between galaxies. Otherwise, they will be easily absorbed by gas and dust floating in the space.
Until now, no galaxy was found having such characteristics. Therefore, a team of international researchers turned to the so-called green pea galaxies. The examined the data from Sloan Digital Sky Survey – a database of millions of galaxies. They choose 5,000 galaxies from the data that emit very intense UV radiation and only five were shortlisted for examiantion through Hubble telescope including green pea galaxy J0925.
Researchers found that the galaxy discharge ionized photons in large numbers and at an intensity that has never seen before. The discovery is a significant step towards solving the mystery of cosmic dark age.
"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," said Trinh.
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"These are crucial observations in the process of stepping back in time to the early universe. They paved the way to future observations with the successor of Hubble, the James Webb Space Telescope, planned for launch in 2018, which is expected to revolutionize the field with updated capabilities for detailing the first galaxies and sources of cosmic re-ionization."