‘Big baby’ galaxy detected in early universe

By Deborah Zabarenko

WASHINGTON (Reuters) – Astronomers using two of NASA’s most
powerful telescopes said on Tuesday they have detected a “big
baby” galaxy, vastly heavy for its young age and its location
in the early universe.

The discovery was surprising, since astronomers have long
theorized that galaxies form when stars gradually cluster
together, with small galaxies preceding bigger galaxies.

But the stars in this cosmic infant — less than 1 billion
years old — have eight times the mass of those in the
13-billion-year-old Milky Way, which contains Earth.

The young galaxy was found by researchers using NASA’s
Hubble and Spitzer space telescopes who looked back in time to
a point some 800 million years after the Big Bang explosion
that many scientists believe gave birth to the universe.

The discovery of this massive, well-developed galaxy at
such an early point in time means astronomers may have to
adjust their ideas on when galaxies and other cosmic objects
can form, said Massimo Stiavelli of the Space Telescope Science
Institute, which deals with Hubble’s findings.

“It means that the process of galaxy formation started
really very early on,” Stiavelli said in a telephone interview.
“It pushes back things like first light, which is the thing we
are all hunting for.”

FOUND IN HUBBLE SURVEY

Before the emergence of the first light source, the
universe is thought to have been suffused with a generic glow,
caused by microwave background radiation from the Big Bang.

The galaxy, known as HUDF-JD2, was hiding in a tiny patch
of sky — about one-tenth the size of the full moon — known as
the Hubble Ultra Deep Field, because the Hubble Space Telescope
made a detailed survey of this area.

Rather than a two-dimensional picture, the Hubble survey is
a bit like a core sample of the cosmos, peering narrowly into
the vast distance of space, and therefore back in time about 13
billion years.

Even Hubble’s keen cameras could not see this galaxy in
visible light; it was only detected in infrared images made by
Hubble and an infrared camera at the European Southern
Observatory in Chile. In general, older astronomical objects
appear redder than younger objects.

The Spitzer telescope, which is sensitive to the light from
older, redder stars, found the baby galaxy to be unexpectedly
bright in infrared light, suggesting a very massive object,
especially for its early era.

“This would be quite a big galaxy even today,” said Mark
Dickinson of the National Optical Astronomy Observatory and
lead scientist for the Spitzer results. “At a time when the
universe was only 800 million years old, it’s positively
gigantic,” Dickinson said in a statement.

These findings are to be reported in November and December
in the Astrophysical Journal.

More information and images are available at

http://hubblesite.org/news/2005/28.