"These galaxies are so young that they existed before many of the atoms in our bodies existed," said James Bullock, a University of California at Irvine physics and astronomy professor who was not involved in the study.
A team of scientists led by Caltech astrophysicist Richard Ellis used NASA's famous orbiting telescope to look deep into a slice of sky known as the Hubble Ultra Deep Field. The researchers hoped to pick up signs of distant galaxies as close to the edge of the universe as Hubble could see, because as they look deeper into space, they're also looking farther back in time.
To determine a galaxy's age, scientists measure what's known as redshift of the light they see coming from it: As the universe rapidly expands and the galaxies speed up, the light from those galaxies is stretched into longer, and redder, wavelengths. From the degree of this redshift, astronomers can determine how fast an object is moving away, and thus how far away it must be. The more extreme the redshift, the farther it must have traveled -- and thus the older Hubble's snapshot of it is.
Astronomers know that universe began in a big bang roughly 13.7 billion years ago because they see evidence of the event in the cosmic background radiation that permeates the universe. They have a good sense of what it looked like in its adolescence and adulthood, because telescopes can look far enough into space to capture snapshots millions and billions of years into the past.
But the earlier period lasting a few hundred million years after the big bang remains something of a mystery, Ellis said -- and this study helps fill in the gaps.
Theoretical astrophysicists have wondered whether the once-dark universe began to light up all at once, as ultraviolet light from the growing number of stars and coalescing galaxies ionized surrounding gas. But Hubble revealed a sloping decline in the number of galaxies as the astronomers looked further away-- and thus farther back in time -- suggesting that this was a gradual process, not a sudden one, Ellis said.
The galaxies the team found were formed about 350 million to 600 million years after the big bang, when the universe was less than 4 percent of its present age -- practically a toddler. This is about as far back as astronomers can look for now, Ellis said. Hubble's successor, the James Webb Space Telescope, will look further into the infrared light spectrum and should pick up galaxies hovering closer to the universe's birth.
The work, accepted for publication by the Astrophysical Journal Letters, teaches researchers about the building blocks that helped form the universe we know today, said Harvard astronomy professor Avi Loeb, who was not involved in the study.
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