SWIRE: Piecing Together the Universe's
History with Wide-Infrared Eyes
Written by Linda Vu
October 27, 2005
Galaxy as seen by Spitzer's SWIRE program.|
NASA/JPL-Caltech/C. Lonsdale (Caltech/IPAC) and
the SWIRE Team
Nowadays much of the universe's matter seems to be organized, as
stars, solar systems, galaxies, and galaxy clusters are familiar
sights of the local universe. However this was not always the case.
According to the Big Bang theory, the universe was created
approximately 13.7 billion years ago when a singular point exploded,
unleashing energy and the fabric of space and time. Galaxies did not
exist in this primordial universe and the extreme temperatures kept
matter from condensing. As the universe expanded and cooled,
protons, neutrons and electrons were created out of this early
intense energy, paving the way for the formation of the elements:
hydrogen and helium and so on. At this point, the long pull of
gravity somehow produced massive clumping of the elements, which
eventually led to the creation of galaxies and other cosmic
By using the Spitzer Space Telescope to conduct a wide-area sky
survey, the Spitzer Wide-area Infrared Extragalactic Survey (SWIRE)
Legacy team hopes to explain how mature nearby galaxies evolved from
the "element clumps" of the early universe.
According to SWIRE Scientist Dr. Jason Surace, Spitzer is
essential for studying the evolution of galaxies because its
unprecedented infrared sensitivity allows astronomers to lift the
dusty veil shrouding infant stars and gain valuable insights into
the process of star formation itself.
"Spitzer is helpful because it brings us actual measurements of
the number of stars forming in a galaxy and can tell us how rapidly
interstellar dust heats up," says Surace.
The rapidly heating dust is important because it offers
astronomers the first window into the star formation process. In the
very beginning stages of star formation, long before a star "turns
on" visibly, heat is emitted as gas and dust contract to form a
star. This heat radiates in the far-infrared and can easily be
detected by Spitzer's Multiband Imaging Photometer (MIPS).
Using the telescope's Infrared Array Camera (IRAC) the team can
observe the history of star formation in galaxies, by studying the
older stars that make up the structure's "skeleton."
"By comparing the rate of star formation with redshift
data from optical telescopes, we learn a lot about galaxies," says
Witnessing the Evolution of
Due to the nature of light travel, distance equals time in space.
In other words, the farther away the object is from Earth the longer
it takes for its light to travel to Earth, thus when scientists
observe objects that are 10 billion light-years away, they are
essentially observing a snapshot of the object from 10 billion years
SWIRE principal investigator Dr. Carol Lonsdale stresses that the
wide-area scans are essential to SWIRE's survey for precisely this
reason. The wider the survey, the more distance and time is covered.
"The wide-area survey allows us to see different types of
galaxies over large distances and large-scale structures like galaxy
clusters," said Lonsdale.
"The ability to observe galaxies over large distances of space
and time will give us a better idea of how galaxies formed and
subsequently evolved, revealing the life cycle of the largest
entities known to science" added SWIRE scientist Dr. Thomas Jarrett.
According to Jarrett, conducting a survey to determine how
galaxies have evolved is like simultaneously witnessing ten
different crime scenes and then trying to solve one of the mysteries
by linking all these crimes together. In the case of SWIRE, each
scientist observes a variety of galaxies at different distances, or
times in the universe's history. After careful analysis, these
astronomers link together their information to solve the mystery of
how galaxies evolved throughout the universe's lifetime.
For example, as a member of the SWIRE Legacy team, Jarrett
studies the local universe, or galaxies that are "only" millions of
light-years away. Meanwhile, Lonsdale and Surace's expertise lay in
researching galaxies billions of light-years away in the distant
universe. After conducting their individual observations, Jarrett,
Lonsdale, Surace, and other members of the team then attempt to
connect their evidence to solve the mystery of how modern galaxies
came to be. Their ultimate goal is to use observations of distant
galaxies to explain behaviors of local galaxies.
"The benefit of working with the local universe is that you can
actually see the structural details of nearby galaxies, for example,
spiral arms, nuclei, and giant star formation regions," says
Because of the current technological limitations, galaxies in the
distant universe can only be detected as fuzzy lights. Despite this,
Spitzer's unprecedented sensitivity allows the telescope to take
pictures of nearby galaxies in unrivaled detail. While the fuzzy
distant galaxies may not provide scientists with detailed images of
galactic behavior in the early universe, these attributes can be
inferred from observations in the local universe. A prime example of
this lays in SWIRE's recent observations of the "Tadpole Galaxy,"
located at a mere 400 million light-years from Earth, an example of
a spectacular gravitational interaction between two galaxies.
Although astronomers recognize that interacting galaxies, or
colliding galaxies, are less frequent occurrences in the local
universe, they believe that this was a fairly common phenomenon in
the early universe. Locally, galaxies are less likely to collide
because over time the expanding universe has increased the distance
between galaxies. Because Spitzer's low image resolution of galaxies
billions of light-years away makes it difficult for scientists to
discern the details of early galaxy interactions, this detailed
image of the Tadpole Galaxy collision gives scientists insight into
what the early galactic collisions may have looked like, and how
this phenomenon helped galaxies evolve into normal galaxies being
observed in the local universe.
According to Surace, a second reason for doing a wide-area survey
is to give astronomers a greater chance of discovering and mapping
Like all the Spitzer Legacy Science projects, although SWIRE has
a specific goal, it was chosen because the information acquired by
its method of research will benefit astronomers across the field. In
addition to studying the evolution of galaxies over the universe's
history, the team will also be mapping the universe in unprecedented
infrared detail for future astronomers. And while all the questions
revolving around the physics of galactic evolution may not be
answered by the end of this particular project, the information that
the team has gathered will lay the foundation for future research.
"Our explicit goal is to see how galaxies evolved over billions
of years," says Surace. "But because of Spitzer's sensitivity and
the large area of our survey, the information that we've collected
will also help scientists studying asteroids, [planet-forming, or]
protoplanetary disks, and star formation."
By the end of this project, SWIRE will produce a catalogue of two
to three million galaxies for Spitzer's public archive.
SWIRE: The Son of WIRE
For many SWIRE astronomers, Spitzer's Legacy Science Program
represents a second chance to study the evolution of galaxies and
the structure of the modern universe. Before they were members of
SWIRE, most of these scientists were part of NASA's Wide-field
Infrared Explorer (WIRE) team. That is why members of the SWIRE
Legacy team often refer to their project as "the Son of WIRE" or,
"S-WIRE" for short.
In March 1999, just a few days into WIRE's four-month mission,
the telescope was declared dead due to a technical malfunction that
caused the spacecraft to eject its protective cover while its
heat-sensitive telescope was still pointing at the hot Earth. This
glitch caused the block of hydrogen ice keeping the craft's
telescope at a cool -436 degrees Fahrenheit to melt and evaporate,
rendering the instrument ineffective.
"When WIRE's mission prematurely ended, we realized that we could
do our technical observations with Spitzer," said Surace. "[Thus]
SWIRE stemmed from WIRE's failed mission and SWIRE inherited its
science team from WIRE, along with many additions, particularly from
According to Jarrett, a group of scientists led by Lonsdale
interested in galaxies proposed the SWIRE Legacy project. Thus, the
project's explicit goal is to survey the sky and study galactic
evolution. However, as members of the astronomical community
realized that detailed information on cosmic objects like asteroids,
comets, and protoplanetary disks would also be captured in the
survey, scientists with varied interests asked to participate and
the team expanded to include them.
"The mission's failure was a tremendous disappointment," said
Surace. "Many of the people associated with WIRE had been working
long hours for more than half a decade only to have all that hard
Using unprecedented technology, WIRE would have surveyed a large
section of the sky at infrared wavelengths of 12 and 25 microns for
extremely bright star clusters called starburst galaxies, which
produce new stars at 10 times the rate of typical galaxies. It would
have also looked at infant galaxies, or protogalaxies, giving
scientists an insight into the process of galaxy, star and solar
system formation. Now with NASA's Spitzer Infrared Telescope and the
SWIRE survey, the major scientific goals of WIRE will finally be