An ancient galaxy has broken the record for the most distant point in the sky known to date, with its light taking roughly 13.1 billion years to reach Earth.
The new record-holder is named UDFy-38135539 and contains roughly a billion stars that would have formed within 600 million years of the Big Bang, which scientists think started the universe 13.7 billion years ago.
The distant galaxy was discovered by the Hubble Space Telescope in 2009. In the new study, researchers used the Very Large Telescope in Chile to observe the galaxy for 16 hours to confirm its distance from Earth by measuring how much its extremely faint glow was distorted by the expansion of the universe. UDFy-38135539 was found to be about 100 million light-years farther than the previous record-holder, a gamma-ray burst.
Clearing out the fog
Scientists are intrigued by UDFy-38135539 because it is the first galaxy known to have lived fully within the so-called epoch of reionization, which they say lasted from about 150 million to 800 million years after the Big Bang.
Back then, intense ultraviolet radiation from the first stars was clearing the opaque fog that filled the cosmos by splitting its hydrogen atoms into electrons and protons, a process known as reionization.
"One of the most dramatic impacts galaxies have had on the whole history of the universe is through reionization," said Matthew Lehnert at the Paris Observatory in France. Lehnert is lead author of the UDFy-38135539 study appearing in the Oct. 21 issue of the journal Nature.
"This is the first time we know for sure that we are looking at one of the galaxies that cleared out the fog which had filled the very early universe," said one of study's co-authors, Nicole Nesvadba at the University of Paris-Sud in France.
Window into the past
UDFy-38135539 may yield key clues into this mysterious time in the universe's history.
For instance, the researchers deduced that a bubble of ionized hydrogen gas at least 6.5 million light-years wide surrounded UDFy-38135539.
Since this bubble seemed larger than what the galaxy could have carved out by its own light, "there must be other galaxies — probably fainter and less-massive nearby companions of UDFy-38135539 — which also helped make the space around the galaxy transparent," said co-author Mark Swinbank at Durham University in England. "Without this additional help, the light from the galaxy, no matter how brilliant, would have been trapped in the surrounding hydrogen fog, and we would not have been able to detect it."
Such tiny galaxies could have been the primary sources of ionization during this epoch, the researchers suggested.
Still, it is possible that it was a flattened bubble that appears large only along our line of sight, they acknowledged. Astronomers would need to examine more galaxies from this time to be sure.
"This is just the type of science that will be routine when ESO's European Extremely Large Telescope — which will be the biggest optical and near infrared telescope in the world — becomes operational," said co-author Jean-Gabriel Cuby of the Laboratory of Astrophysics of Marseille in France.
Previous cosmic distance records
The galaxy UDFy-38135539 joins an elite group of far-flung cosmic objects in the distant regions of the universe.
Until now, the object known to be the most distant in the universe was the gamma-ray burst discovered just last year, whose light took about 13 billion years to reach here. The most remote galaxy was IOK-1, whose light took 12.88 billion years to reach Earth.
Although the difference in age of 100 million years or so between that gamma-ray burst and UDFy-38135539 might not seem like much, "in that time, the universe changes rather dramatically — reionization happened over just a few hundred million years," Lehnert told SPACE.com.
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