"The New York Times" August 7, 2001
Astronomers See Evidence of First Light in Universe
By JAMES GLANZ
A team of astronomers announced yesterday that it had found what it
called the cosmic renaissance, the epoch in which starlight first
began streaming freely through the universe.
The announcement was made a few days after another team reported
that it had discovered the cosmic dark ages, a time before stars
and galaxies began shining.
The new finding appears to strengthen the scientific case that
after decades of searching, telescopes on Earth have finally looked
far enough back in time to glimpse the epoch in which stars and
galaxies first formed. It comes from a team led by Dr. S. George
Djorgovski, an astrophysicist at the California Institute of
Technology.
But while last week's announcement, by members of the Sloan
Digital Sky Survey, a team involved an apparent peek into the dark
ages themselves, the latest observations amount to a snapshot of
part of the universe just over a hundred million years later.
Considering that scientists believe that the universe was born
in
a great explosion some 13 billion years ago and that, according to
the Sloan findings, the dark ages ended when the universe was
roughly 900 million years old, that difference may not sound like
much. But like the historical leap from Byzantine devotional
paintings to the frescoes of the Renaissance, that short span made
all the difference, scientists say.
"It's like the difference between when you have water and when
it's shifted to ice," said Dr. Daniel Stern, an astrophysicist at
the Jet Propulsion Laboratory in Pasadena, Calif., who is a member
of the Caltech team. "The universe has gone through this rapid
change in a short period of time."
Both sets of measurements focused on a kind of fog or haze that
is
thought to have pervaded the universe during the dark ages before
it was dissipated by the light of the first stars, galaxies and
other celestial structures that eventually formed in the universe.
The Sloan observations looked at that fog in the light of the
most
distant known object in the universe, a quasar, or cosmic beacon
with a brightness equivalent to billions of suns. The quasar seems
to have been shining just as the dark ages were ending.
By contrast, Dr. Djorgovski's team, which also included Dr. Sandra
Castro and Dr. Ashish Mahabal, both at Caltech, examined a quasar
that is slightly less distant and therefore emitted its light a
little more than a hundred million years more recently, after the
dark ages apparently ended.
Like two distant streetlights, one inside a fog bank and one
outside, the quasars appear different when observed with powerful
telescopes, apparently confirming that the universe went through a
major change when it was about 900 million years old.
"I think this is fairly inspiring," said Dr. David H. Weinberg,
an
astrophysicist at Ohio State University who is a member of the
Sloan team. "Certainly the two together are more persuasive than
either alone."
Several scientists voiced much less confidence on the Caltech
team's claim that they have observed wisps, or remnants, of dark-
age fog still wafting through the universe during the cosmic
renaissance.
Dr. Abraham Loeb, an astrophysicist at Harvard, said persistence
of the fog, which is thought to be neutral hydrogen gas, would be
important in understanding how structures formed in the early
universe if the claim was correct. But he said the Caltech
observations had not settled that question. "I think it deserves
more analysis," Dr. Loeb said.
Both teams have made papers on the observations available on an
electronic archive where scientists often place their new results:
arXiv.org/abs/astro-ph/0108069 and arXiv.org/abs/astro-ph/0108097.
The papers were scheduled to be available yesterday as of midnight.
About half a million years after the Big Bang, the universe
cooled and entered the dark ages, which lasted for hundreds of
millions of years and ended only when enough stars and galaxies
formed so that their light dissipated the fog =8B or, in technical
terms, ionized the hydrogen gas pervading the universe.
Sir Martin Rees, a cosmologist at Cambridge University, said that
however the question of the possible renaissance fog was eventually
resolved, the real issue was learning about the history of light
sources in the cosmos.
"The important thing is that observations are now pinning down
how
the first sources in the universe built up in strength," Sir Martin
said.
POWRÓT