NASA's Hubble
and Spitzer space telescopes, with a boost from a natural
"zoom lens," have
uncovered what may be one of the youngest and brightest
galaxies ever seen in the middle of the
cosmic "dark ages," just 700 million years after the
beginning of our universe.
The detailed images from Hubble's Near Infrared Camera
and Multi-Object Spectrometer,
known as NICMOS, reveal an infant galaxy, dubbed A1689-zD1,
undergoing a firestorm of star birth
during the dark ages, a time shortly after the Big Bang but
before the first stars reheated the cold,
dark universe. Images from NASA's Spitzer Space Telescope's
Infrared Array Camera provided
strong additional evidence that it was a young star-forming
galaxy in the dark ages.
The team conducting the study was led by Larry
Bradley, an associate research scientist in the
Henry A. Rowland
Department of Physics and Astronomy at Johns
Hopkins.
The new images should offer insights into the
formative years of galaxy birth and evolution and
yield information on the types of objects that may have
contributed to ending the dark ages. The
faraway galaxy also is an ideal target for Hubble's
successor, the James Webb Space Telescope, or
JWST, scheduled to launch in 2013.
During its lifetime, the Hubble telescope has peered
ever further back in time, viewing galaxies
at successively younger stages of evolution. These
snapshots have helped astronomers create a
scrapbook of galaxies from infancy to adulthood. The new
Hubble and Spitzer images of A1689-zD1
show a time when galaxies were in their infancy.
Current theory holds that the dark ages began about
400,000 years after the Big Bang as
matter in the expanding universe cooled and formed clouds
of cold hydrogen. These cold clouds
pervaded the universe like a thick fog. At some point
during this era, stars and galaxies started to
form. Their collective light reheated the foggy, cold
hydrogen, ending the dark ages about a billion
years after the Big Bang.
"This galaxy presumably is one of the many galaxies
that helped end the dark ages," Bradley
said. "Astronomers are fairly certain that high-energy
objects such as quasars did not provide enough
energy to end the dark ages of the universe. But many young
star-forming galaxies may have produced
enough energy to end it."
The galaxy is so far away that it did not appear in
images taken with Hubble's Advanced Camera
for Surveys, because its light is stretched to invisible
infrared wavelengths by the universe's
expansion. It took Hubble's NICMOS, Spitzer and a trick of
nature called gravitational lensing to see
it.
The astronomers used a relatively nearby massive
cluster of galaxies known as Abell 1689,
roughly 2.2 billion light-years away, to magnify the light
from the more distant galaxy directly behind
it. This natural telescope is called a gravitational
lens.
Though the diffuse light of the faraway object is
nearly impossible to see, gravitational lensing
has increased its brightness by nearly 10 times, making it
bright enough for Hubble and Spitzer to
detect. A telltale sign of the lensing is the smearing of
the images of galaxies behind Abell 1689 into
arcs by the gravitational warping of space by the
intervening galaxy cluster.
The images reveal bright, dense clumps of hundreds of
millions of massive stars in a compact
region about 2,000 light-years across, a width that is only
a fraction of the Milky Way's. This type of
galaxy is not uncommon in the early universe, when the bulk
of star formation was taking place,
Bradley said.
Spitzer's images show that the galaxy's mass is
typical to those of galaxies in the early universe.
Its mass is equivalent to several billions of stars like
our sun, or just a tiny fraction of the mass of
the Milky Way.
"This observation confirms previous Hubble studies
that star birth happens in very tiny regions
compared with the size of the final galaxy," said team
member Garth Illingworth, of the University of
California, Santa Cruz.
Even with the increased magnification from the
gravitational lens, Hubble's sharp "eye" can see
only knots of the brightest, heftiest stars in the galaxy.
The telescope cannot pinpoint fainter, lower-
mass stars, individual stars or the material surrounding
the star-birthing region. To see those things,
astronomers will need the infrared capabilities of NASA's
JWST. The planned infrared observatory
will have a mirror about seven times the area of Hubble's
primary mirror and will collect more light
from faint galaxies. JWST also will be able to view even
more remote galaxies whose light has been
stretched deep into infrared wavelengths that are out of
the reach of NICMOS.
"This galaxy will certainly be one of the first
objects that will be observed by JWST," said
team member Holland Ford, a professor of physics and
astronomy at Johns Hopkins. "This galaxy is so
bright that JWST will see its detailed structure. This
object is a pathfinder for JWST for
deciphering what is happening in young galaxies."
The astronomers noted that the faraway galaxy also
would be an ideal target for the Atacama
Large Millimeter Array, which, when completed in 2012, will
be the most powerful radio telescope in
the world. "ALMA and JWST working together would be an
ideal combination to really understand this
galaxy," Illingworth said. "JWST's images and ALMA's
measurement of the gas motions will provide
revolutionary insights into the very youngest galaxies."
The astronomers will conduct follow-up observations
with infrared spectroscopy to confirm the
galaxy's distance using the Keck telescope atop Mauna Kea
in Hawaii.
The results will be published in the Astrophysical
Journal.
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