New Cambridge light on cosmic `dark ages`

Remnants of the first stars have helped astronomers get closer on cosmic `dark ages`.

Updated: Jan 09, 2011, 16:28 PM IST

London: Remnants of the first stars have
helped astronomers from the University of Cambridge and the
California Institute of Technology get closer to unlocking the
"dark ages" of the cosmos.

A team of researchers from the two centres of learning
are using light emitted from massive black holes called
quasars to "light up" gases released by the early stars, which
exploded billions of years ago.

As a result, they have found what they refer to as the
missing link in the evolution of the chemical universe, a
University of Cambridge release said.

The first stars are believed to hold the key to one of
the mysteries of the early cosmos: how it evolved from being
predominantly filled with hydrogen and helium to a universe
rich in heavier elements, such as oxygen, carbon and iron.

However, although telescopes can detect light reaching
Earth from billions of light-years away, enabling astronomers
to look back in time over almost all of the 13.7-billion-year
history of the universe, one observational frontier remains:
the so-called "dark ages".

This period, lasting half a billion years after the
Big Bang, ended when the first stars were born and is
inaccessible to telescopes because the clouds of gas that
filled the universe were not transparent to visible and
infrared light.

"We have effectively been able to peer into the dark
ages using the light emitted from a quasar in a distant galaxy
billions of years ago.

The light provides a backdrop against which any gas
cloud in its path can be measured," said Professor Max Pettini
at Cambridge`s Institute of Astronomy (IoA), who led the
research with PhD student Ryan Cooke.

Taking precision measurements using the world`s
largest telescopes in Hawaii and Chile, the researchers have
used Quasar Absorption Line Spectroscopy to identify gas
clouds called `damped Lyman alpha systems` (DLAs).

Among the thousands of DLAs known, the team have
succeeded in finding a rare cloud released from a star very
early in the history of the universe.

"As judged by its composition, the gas is a remnant of
a star that exploded as much as 13 billion years ago," Pettini

"It provides the first analysis of the interior of
one of the universe`s earliest stars." The results provide experimental observations of a
time that has so far been possible to model only with
computers simulations, and will help astronomers to fill gaps
in understanding how the chemical universe evolved.

"We discovered tiny amounts of elements present in the
cloud in proportions that are very different from their
relative proportions in normal stars today.

Most significantly, the ratio of carbon to iron is 35
times greater than measured in the Sun," Pettini said.

"The composition enables us to infer that the gas
was released by a star 25 times more massive than the Sun and
originally consisting of only hydrogen and helium.

In effect this is a fossil record that provides us
with a missing link back to the early universe."

The study was published in Monthly Notices of the
Royal Astronomical Society by Ryan Cooke, Max Pettini and
Regina Jorgenson at the IoA, together with Charles Steidel and
Gwen Rudie at the California Institute of Technology in