What Was Old Could Be New Again
NASA's Galaxy Evolution
Explorer has spotted what appear to be massive "baby" galaxies in
our corner of the universe. Previously, astronomers thought the
universe's birth rate had dramatically declined and only small
galaxies were forming.
"We knew there were really massive young galaxies eons ago, but
we thought they had all matured into older ones more like our Milky
Way. If these galaxies are indeed newly formed, then this implies
parts of the universe are still hotbeds of galaxy birth," said Dr.
Chris Martin. He is principal investigator for the Galaxy Evolution
Explorer at the California Institute of Technology, Pasadena, CA,
and co-author of the study.
Martin and colleagues, led by Dr. Tim Heckman of Johns Hopkins
University, Baltimore, MD, unearthed three-dozen bright, compact
galaxies that greatly resemble the youthful galaxies of more than
10 billions years ago. These new galaxies are relatively close to
us, ranging from two to four billion light-years away. They may be
as young as 100 million to one billion years old. The Milky Way is
approximately 10 billion years old.
The recent discovery suggests our aging universe is still alive
with youth. It also offers astronomers their first, close-up
glimpse at what our galaxy probably looked like when it was in its
infancy.
"Now we can study the ancestors to galaxies much like our Milky
Way in much more detail than ever before," Heckman said. "It's like
finding a living fossil in your own backyard. We thought this type
of galaxy had gone extinct, but in fact newborn galaxies are alive
and well in the universe," he added.
The new discoveries are of a type called ultraviolet luminous
galaxies. They were discovered after the Galaxy Evolution Explorer
scanned a large portion of the sky with its highly sensitive
ultraviolet light detectors. Since young stars pack most of their
light into ultraviolet wavelengths, young galaxies appear to the
spacecraft like diamonds in a field of stones. Astronomers mined
for these rare gems before, but missed them because they weren't
able to examine a large enough slice of the sky.
"The Galaxy Evolution Explorer surveyed thousands of galaxies
before finding these few dozen ultraviolet-bright ones," said Dr.
Michael Rich, a co-author of the study from the University of
California, Los Angeles.
The newfound galaxies are about 10 times as bright in
ultraviolet wavelengths as the Milky Way. This indicates they are
teeming with violent star-forming regions and exploding supernova,
which are characteristics of youth.
When our universe was young, massive galaxies were regularly
bursting into existence. Over time, the universe bore fewer and
fewer galactic progeny, and its newborn galaxies grew up into ones
that look like our own. Until now, astronomers thought they had
seen the last of these giant babies.
The results will be published in an upcoming special issue of
Astrophysical Journal Letters, along with several other papers
describing new results from the Galaxy Evolution Explorer.
The Galaxy Evolution Explorer was launched on April 28, 2003.
Its mission is to study the shape, brightness, size and distance of
galaxies across 10 billion years of cosmic history. The Explorer's
50-centimeter-diameter (19.7-inch) telescope sweeps the skies in
search of ultraviolet-light sources.
Caltech leads the Galaxy Evolution Explorer mission and is
responsible for science operations and data analysis. NASA's Jet
Propulsion Laboratory, Pasadena, CA, manages the mission and built
the science instrument. The mission was developed under NASA's
Explorers Program managed by the Goddard Space Flight Center,
Greenbelt, MD. South Korea and France are the international
partners in the mission.