Clutch of Distant Galaxies Reveals Infant Universe: Hubble Captures Cosmic Structure First Taking Shape
Witze, Alexandra, Science News
Peering into the far reaches of the universe, astronomers have spotted seven galaxies so distant that they appear as they did less than 600 million years after the Big Bang.
Finding so many primordial galaxies allows scientists to pin down crucial questions about the newborn universe, such as when light from early stars and galaxies first penetrated the early cosmic gloom. "It's the scientific study of Genesis," says Avi Loeb, a Harvard astronomer who was not involved in the work.
The discovery comes from the hardworking Hubble Space Telescope, which in August and September spent more than 100 hours staring deeply into a small patch of sky. That region, in the southern constellation Fornax, is the same one that was targeted in 2009 for a long-duration exposure known as the Hubble Ultra Deep Field.
Astronomers led by Caltech's Richard Ellis looked there again, but for longer exposure times and with an additional filter that's sensitive to the faint, red light of faraway galaxies. The new census, to appear in an upcoming Astrophysical Journal Letters, includes seven galaxies at great distances--including one that might be the record-breaker of them all, seen as it was just 380 million years after the Big Bang.
Because the cosmos has been expanding since the Big Bang, 13.7 billion years ago, light from these very distant objects has only now arrived at Earth--and so they appear as they did during the universe's infancy. The distance to such faraway objects is usually stated in terms of redshift; the higher the redshift, the more distant the object.
The seven galaxies described by Ellis and his team all have redshifts higher than 8.5. One of them may even be as high as redshift 11.9, Ellis says. That galaxy, named UDFj-39546284, was spotted earlier by other astronomers who pegged it at a redshift of 10.5 (SN Online: 1/26/11). Hubble data suggest it may be even more distant, Ellis says.
Another recent Hubble survey also found a handful of faraway galaxies with redshifts possibly in the range of 8.5 to 10. That survey is called CLASH, for the Cluster Lensing and Supernova Survey with Hubble. It looks for distant objects whose light has been bent and magnified by the gravitational influence of galaxies lying in the line of sight between the faraway objects and observers on Earth or in orbit around it. This effect boosts the light of dim objects, making them easier to see.
In November, astronomers with CLASH announced finding a galaxy with a redshift of 10.8 in the constellation Camelopardalis. In September, CLASH reported a redshift-9.6 galaxy in the constellation Leo. "Broadly speaking, their results are consistent with ours," says James Dunlop, an astronomer at the University of Edinburgh who works with Ellis.
More important than any record-breaker, says Ellis, is what a census of distant galaxies can say about how and when the early universe lit up (see Back Story).
About 400,000 years after the Big Bang, hydrogen gas formed throughout the newborn universe. But not until some 200 million years later did those clouds of hydrogen grow dense enough to gravitationally collapse and ignite fusion in the hearts of the first stars. …