Astronomers have found the most distant galaxy yet, a discovery that pushes back scientists' view of the universe to about 700 million years after it is thought to have come into existence.
The universe is thought to be about 13.8 billion years old.
Light from the galaxy, designated by scientists as z8_GND_5296, took about 13.1 billion years to reach the orbiting Hubble Space Telescope and the Keck Observatory in Hawaii, both of which detected the galaxy in infrared light.
"We are learning so much about a region so far back in time it's hard to comprehend. This galaxy we're seeing is almost 13.1 billion years ago and so this was something like 8 billion years before our sun was even born and of course much longer after that until life came around," said lead researcher Steven Finkelstein, an assistant professor with the University of Texas at Austin.
Surprisingly, out of a pool of 43 candidate distant galaxies, z8_GND_5296 was the only one that revealed the key chemical evidence needed to confirm its distance.
Although some more-distant candidate galaxies have been detected, they have not yet been confirmed in this way.
Key moment in universe's history
The discovery left Finkelstein and colleagues wondering if they had uncovered a clue to a bigger mystery: How soon did light from the universe's first stars and galaxies pierce an obscuring veil of hydrogen gas that existed early in its history?
Scientists believe that at some point, high-energy ultraviolet radiation from exploded stars split the intergalactic hydrogen atoms into electrons and protons. Once ionized, the hydrogen would be electrically conductive and no longer scatter light.
That may have happened about the time of z8_GND_5296's existence.
The galaxy, which is about a billion times as massive as the sun, has two unusual characteristics, which may be a factor in why it is visible, while potential sister galaxies are not.
First, z8_GND_5296 is forming stars at a very fast pace, pumping out about 100 times more stars than the Milky Way galaxy, so it may be brighter than the other candidate galaxies.
Second, it contains a surprisingly high percentage of elements heavier than hydrogen and helium.
Those elements are forged by nuclear fusion inside stars, so either the galaxy contains the exploded remains of lots of massive stars or it formed in a region of space that had been previously seeded with the remnants of a prior generation of stars, scientists said.
"It could be that this one galaxy lives in an over-dense region of (ionized hydrogen) so we can see it ... but that's a little bit of conjecture. For all we know these other galaxies have just a lot more hydrogen gas within the galaxies themselves and that's why we can't see them," Finkelstein said.
He and colleagues hope to conduct a wider survey for ancient galaxies with Hubble, but more details about z8_GND_5296 will likely have to wait until NASA launches its successor observatory, the James Webb Space Telescope, targeted for launch in 2018.
The research appears this week in the journal Nature.