FEATURE1 BIG BANG
This is said to be the deepest image of the Universe ever taken in near-infrared light by the Hubble Space Telescope. The faintest and reddest objects (left inset) in the image are galaxies that correspond to times of approximately 12.9 billion years to 13.1 billion years ago. No galaxies have been seen before at such early epochs
The Hubble Space Telescope has peered further back in space and time than ever before to see baby galaxies that may have formed as little as 500 million years after the Big Bang.
Observations with a new camera installed on the orbiting telescope last year have revealed an ancient cosmic “undiscovered country” of primitive galaxies, which date back to the infancy of the Universe.
Astronomers estimate that three newly-identified galaxies, which are small and compact and glow a striking blue, are about 13.2 billion light years away. The starlight that Hubble has captured was thus emitted some 13.2 billion years ago, when the Universe was just 4 per cent of its present age.
If these preliminary calculations of distances and dates are confirmed, the galaxies would be the oldest and farthest away yet observed, offering new insights into the earliest years of the cosmos.
“With the rejuvenated Hubble and its new instruments, we are now entering unchartered territory that is ripe for new discoveries,” said Garth Illingworth, of the University of California, Santa Cruz (UCSC), who led the survey team.
He told the American Astronomical Society conference in Washington that the updated Hubble observatory provides an opportunity to “push back the frontiers of the searches for the first galaxies and to explore their nature”.
Further clues to the early Universe have been provided by a another remarkable image, a mosaic which combines pictures from Hubble’s new camera with an older survey taken in 2004, which was also presented at the Washington conference.
It gives a panoramic view of a slice of sky covering about a third of the diameter of the full moon, containing some 7,500 galaxies at many different stages of evolution.
The early galaxies detected by Dr Illingworth’s team were pinpointed from data collected by Hubble in August last year, following the installation of the telescope’s new Wide Field Camera 3 (WFC3) in May.
The instrument was pointed at a section of sky known as the Hubble Ultra Deep Field, which was first surveyed in visible light in 2004 to provide one of the telescopes’ most iconic images — dark sky teeming with more than 10,000 galaxies. The WFC3 instrument has now repeated the exercise for infrared light.
The first analysis of the new 2009 Hubble Ultra Deep Field (HUDF09), released last month, found faint objects that were formed about 600 million years after the Big Bang. Dr Illingworth’s team has now found evidence that three galaxies in the image date back still further, to about 500 million years after the dawn of the Universe.
As the distance travelled by light increases, its wavelength becomes shifted towards the red end of the spectrum because of the expansion of the Universe — a phenomenon known as redshift that scientists can use to calculate the age of galaxies.
Preliminary calculations have suggested that the redshift value for three very faint galaxies in the new Ultra Deep Field is 10, which equates to an age of about 13.2 billion years, or 500 million years after the Big Bang.
The research has not yet been peer-reviewed, though the scientists have posted a paper online and submitted it to the journal Nature. It has also been reported by the magazine Science News.
The primordial galaxies are much smaller than modern ones, and are thought to have coalesced to give birth to the much larger bodies that exist today, scientists said.
Marcella Carollo, of the Swiss Federal Institute of Technology in Zurich, another member of the research team, said: “They are the very building blocks from which the great galaxies of today, like our own Milky Way, ultimately formed.”
The stars that make up the primitive galaxies must have been formed still earlier than the galaxies themselves, but Hubble is not capable of looking back further into space and time to see them directly. The more powerful James Webb Space Telescope should be able to search for them when it is launched in 2014.
Rychard Bouwens, of UCSC, the lead author of the paper, said: “The faintest galaxies are now showing signs of linkage to their origins from the first stars. They are so blue that they must be extremely deficient in heavy elements, thus representing a population that has nearly primordial characteristics.”
“This is about as far as we can go to do detailed science with the new HUDF09 image,” Dr Illingworth said. “This shows just how much the James Webb Space Telescope is needed to unearth the secrets of the first galaxies.”
(mark henderson, Times Online, 5January2010)
