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| This new image of the Hubble Ultra Deep Field (HUDF) 2012 campaign reveals a previously unseen population of seven faraway galaxies, which are observed as they appeared in a period 350 million to 600 million years after the big bang. Credit: NASA, ESA, R. Ellis (Caltech), and the UDF 2012 Team |
Using NASA's Hubble Space
Telescope, astronomers have uncovered a previously unseen population of seven
primitive galaxies that formed more than 13 billion years ago, when the
universe was less than 4 percent of its present age. The deepest images to date
from Hubble yield the first statistically robust sample of galaxies that tells
how abundant they were close to the era when galaxies first formed.
The results are from an ambitious Hubble
survey of an intensively studied patch of sky known as the Ultra Deep Field
(UDF). In the 2012 campaign, called UDF12, a team of astronomers led by Richard
Ellis of the California Institute of Technology in Pasadena used Hubble's Wide
Field Camera 3 (WFC 3) to peer deeper into space in near-infrared light than
any previous Hubble observation.
The observations were made during six weeks in
August and September, and the first scientific results now are appearing in a
series of scientific papers. The UDF12 team is releasing these unique data to
the public after preparing them for other research groups to use.
The results show a smooth decline in the
number of galaxies looking back in time to about 450 million years after the
big bang. The observations support the idea galaxies assembled continuously
over time and also may have provided enough radiation to reheat, or re-ionize,
the universe a few hundred million years after the theorized big bang.
Looking deeper into the universe also means
peering further back in time. The universe is estimated to be 13.7 billion
years old. The newly discovered galaxies are seen as they looked 350 to 600
million years after the big bang. Their light is just arriving at Earth now.
Astronomers study the distant universe in
near-infrared light because the expansion of space stretches ultraviolet and
visible light from galaxies into infrared wavelengths, a phenomenon called
"redshift." The more distant a galaxy, the higher its redshift.
The greater depth of the new Hubble images,
together with a carefully designed survey strategy, allows this work to go
further than previous studies, thereby providing what researchers say is the
first reliable census of this epoch. Notably, one of the galaxies may be a
distance record breaker, observed 380 million years after the birth of our universe
in the big bang, corresponding to a redshift of 11.9.
A major goal of the new program was to
determine how rapidly the number of galaxies increases over time in the early
universe. This measure is the key evidence for how quickly galaxies build up
their constituent stars.
"Our study has taken the subject forward
in two ways," Ellis explained. "First, we have used Hubble to make
longer exposures. The added depth is essential to reliably probe the early
period of cosmic history. Second, we have used Hubble's available color filters
very effectively to more precisely measure galaxy distances."
The team estimated the galaxy distances by
studying their colors through a carefully chosen set of four filters at
specific near-infrared wavelengths. "We added one filter, and undertook
much deeper exposures in some filters than in earlier work, in order to
convincingly reject the possibility that some of our galaxies might be
foreground objects," said team member James Dunlop of the Institute for
Astronomy at the University of Edinburgh in Scotland.
Astronomers have long debated whether hot
stars in such early galaxies could have provided enough radiation to warm the
cold hydrogen that formed soon after the big bang. This process, called
"re-ionization," is thought to have occurred 200 million to 1 billion
years after the birth of the universe. This process made the universe
transparent to light, allowing astronomers to look far back into time. The
galaxies in the new study are seen in this early epoch.
"Our data confirm re-ionization was a
gradual process, occurring over several hundred million years, with galaxies
slowly building up their stars and chemical elements," said Brant
Robertson of the University of Arizona in Tucson. "There wasn’t a single dramatic
moment when galaxies formed. It was a gradual process."
Thanks for sharing those pics.
ReplyDeleteProducer Chris Young