Distant galaxies near edge of universe's cosmic dawn
Squinting deep into the universe, the Hubble Space Telescope has
picked out what may be the most distant galaxy yet found, observed as it
appeared about 380 million years after the big bang, astronomers said
last Week.
This potential record-breaker is one of seven newly discovered
galaxies formed more than 13 billion years ago, right near the cosmic
dawn, the era when the first big galaxies formed.
"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 travelled - and thus the older Hubble's snapshot of
it is. Astronomers know that the 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 ionised 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 four
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.
-Los Angeles Times
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