Caption: The center of the Abell 370 cluster field seen in red optical (I + Z) and infrared (J+K’) light. The arrow shows the position of the z=6.56 galaxy. Numerous arcs show gravitational lensing of faint galaxies behind the cluster by the mass of the many galaxies in the cluster’s core. The horizontal streaks are due to stars just outside the field of the picture. The image combines 8 hours of infrared exposures on the Subaru 8.3-m telescope with 7 hours exposure in red optical light on the Keck I 10-m telescope, both on Mauna Kea. The galaxy can be seen, though very faintly, at these wavelengths.

An international team led by astronomers from the
University of Hawaii reported discovery of a
galaxy which gives the earliest glimpse of the
epoch when galaxies and stars formed in the

“This galaxy is forming stars at a time speculated
to be in the ‘Dark Ages’ of the universe when
galaxies begin to ‘turn on’,” said University of
Hawaii professor Esther Hu, who led the team.

According to the generally accepted picture, the
universe started with the Big Bang some 14-16 billion
years ago. As the universe expanded and cooled over
the next half billion years, the glowing plasma of
which it was composed recombined into atoms of
neutral gas — mostly hydrogen and some helium.
The glow from this era of recombination has been
observed as the cosmic microwave background
radiation, and used to study the large-scale
geometry of the universe. Over the next nearly
half billion years, termed the Dark Ages, the
cold gas began to assemble into the first galaxies.
The Dark Ages ended as the light from the newly
formed galaxies and quasars reionized and changed
the character of the surrounding neutral gas.

Till now the earliest probes of the Universe have
been quasars, which are extremely luminous distant
objects, believed to be powered by black holes.
To capture an early snapshot of galaxies, which
are typically a thousand times fainter, researchers
concentrated on a bright hydrogen emission line
dubbed “Lyman alpha” that is strongly excited during
star formation. Since a large fraction of the light
from early forming galaxies emerges in this line,
distant galaxies can look prominent viewed through
filters which only pass wavelengths near the Lyman
alpha emission but appear faint or undetected when
seen through other filters.

The method of discovering distant galaxies by
searching for objects identified as “Lyman alpha
emitters” by the sharp increase in their
detectability in narrow bandpass filters has been
very successful, and team members had previously
used one of the giant Keck 10-m telescopes to find
the most distant galaxy previously known, an object
whose light took some 15.3 billion years to reach us.

In order to reach fainter and yet more distant
galaxies in the present work, Hu and her colleagues
used a gravitational lens, in the form of a massive
cluster galaxies to further amplify the light.
According to Einstein’s theory of general relativity,
very massive objects can bend and focus light in much
the same way as a magnifying glass. The astronomers
used the cluster Abell 370, which is 6 million light
years away and whose core contains the mass of
several hundred galaxies, to magnify light from a
galaxy behind the cluster that is 15.5 billion light
years distant.

The discovery images made with the 10-m Keck I
telescope were confirmed with spectra obtained later
on the same telescope which showed there was indeed
a strong Lyman alpha emission line.

“It’s significant that you can see the line,” said
Peter Capak, a University of Hawaii graduate student
and team member. “If only a few galaxies had turned
on by this point the emission would have been
smothered by the surrounding hydrogen gas and the
light would never have made it out to us.”

Len Cowie, another Hawaii astronomer and team member
added, “The fact that this is a galaxy, and not a
quasar, is also important. When the first galaxies
form, it’s like turning on lights to clear out a
fog bank. Quasars are really bright though rare,
so they can make large clear cavities around
themselves, but the fact that light from the
fainter but much more numerous galaxies is getting
out means that a significant amount of early star
formation has already taken place and much of the
general fog has already dissipated.”

The newly discovered galaxy has a redshift of
6.56, and samples the universe when it is about
780 million years old. This is about 50 million
years earlier than the view supplied by the most
distant quasar (redshift = 6.28), and 80 million
years earlier than the speculated period of
reionization (redshift ~6.1).

Since most of the light from these galaxies has
been redshifted to infrared wavelengths, the
team followed up their discovery with infrared
images on the Subaru 8.3-m Telescope, also on
Mauna Kea, to estimate the star formation
rate — finding that 40 times the mass of
the Sun is being turned into new stars each year.

“You want to catch galaxies in their infancy and
see how they develop”, commented Hu. “Scaling the
age of the Universe to a person’s lifetime, we’re
showing you baby pictures. The last galaxy
snapshot showed a toddler just past his fourth
birthday. This one is three and a half.”

“This is good news for the Next Generation Space
Telescope planned for launch in the next decade,”
she concluded. “It means that there should be
plenty of these distant galaxies bright enough
to observe, using a large telescope with good
infrared detectors, above the strong airglow of
our atmosphere.”

Images and additional information about distant
galaxy searches are available at:

The paper will appear in the April 1 issue of the
Astrophysical Journal Letters. The paper has been posted
the public archive and should appear this Friday at:

The Institute for Astronomy at the University of
Hawaii conducts research into galaxies, cosmology,
stars, planets, and the Sun. Its faculty and
staff are also involved in astronomy education,
and in the development and management of the
observatories on Haleakala and Mauna Kea. Refer to for more information.