[Spitzer News] Spitzer Sees Shining Stellar Sphere
spitzer-news at lists.ipac.caltech.edu
spitzer-news at lists.ipac.caltech.edu
Thu Apr 10 14:55:31 PDT 2008
In this issue:
1) Spitzer Sees Shining Stellar Sphere
2) Spitzer Spots Ancient Cosmic Urban Sprawl
3) Cosmic Searchlights Reveal "Lost" Galaxies
SPITZER SEES SHINING STELLAR SPHERE
Millions of clustered stars glisten like an iridescent opal in a new
image from NASA's Spitzer Space Telescope.
Called Omega Centauri, this sparkling orb of stars is like a
miniature galaxy. It is the biggest and brightest of the more than
150 similar objects, called globular clusters, that orbit around the
outside of our Milky Way galaxy. Stargazers at southern latitudes can
spot the stellar gem with the naked eye in the constellation Centaurus.
While the visible-light observations highlight the cluster's millions
of jam-packed stars, Spitzer's infrared eyes reveal the dustier, more
evolved stars tossed throughout the region.
"Now we can see which stars form dust and can begin to understand how
the dust forms and where it goes once it is expelled from a star,"
said Martha Boyer of the University of Minnesota, Twin Cities. Boyer
is lead author of a paper about Omega Centauri appearing in the April
issue of the Astronomical Journal. "Surprisingly, Spitzer revealed
fewer of these dusty stars than expected."
Globular clusters are some of the oldest objects in our universe.
Their stars are more than 12 billion years old, and, in most cases,
formed all at once when the universe was just a toddler. Omega
Centauri is unusual in that its stars are of different ages and
possess varying levels of metals, or elements heavier than boron.
Astronomers say this points to a different origin for Omega Centauri
than other globular clusters: they think it might be the core of a
dwarf galaxy that was ripped apart and absorbed by our Milky Way long
In the new picture of Omega Centauri, the red- and yellow-colored
dots represent the stars revealed by Spitzer. These are the more
evolved, larger, dustier stars, called red giants. The stars colored
blue are less evolved, like our own sun, and were captured by both
Spitzer's infrared eyes and in visible light by the National Science
Foundation's Blanco 4-meter telescope at Cerro Tololo Inter-American
Observatory in Chile. Some of the red spots in the picture are
distant galaxies beyond our own.
"As stars age and mature into red giants, they form dust grains,
which play a vital role in the evolution of the universe and the
formation of rocky planets," said Jacco van Loon, the study's
principal investigator at Keele University in England. "Spitzer can
see this dust, and it was able to resolve individual red giants even
in the densest central parts of the cluster."
NASA's Hubble Space Telescope and Gemini Observatory on Cerro Pachon
in Chile recently found evidence that Omega Centauri is home to a
medium-sized black hole -- http://hubblesite.org/newscenter/archive/
Other authors of the paper include Iain McDonald and Nye Evans of
Keele University; Robert Gehrz and Charles Woodward of the University
of Minnesota; and Andrea Dupree of the Harvard-Smithsonian Center for
Astrophysics, Cambridge, Mass.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the
Spitzer Space Telescope mission for NASA's Science Mission
Directorate, Washington. Science operations are conducted at the
Spitzer Science Center at the California Institute of Technology,
also in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared
array camera, which took the Omega Centauri picture, was built by
NASA's Goddard Space Flight Center, Greenbelt, Md. The instrument's
principal investigator is Giovanni Fazio of the Harvard-Smithsonian
Center for Astrophysics.
Cerro Tololo Inter-American Observatory is part of the National
Optical Astronomy Observatory, which is operated by the Association
of Universities for Research in Astronomy under contract with the
National Science Foundation.
SPITZER SPOTS ANCIENT COSMIC URBAN SPRAWL
The universe's first "galactic cities" did not sprout up randomly
across space. On the contrary, a new statistical analysis of
observations from NASA's Spitzer Space Telescope confirms that these
ancient galactic metropolises may have developed much like sprawling
cities joining together into a larger urban whole.
Across the cosmos, galaxies rarely stand alone. Instead, they are
grouped into large, densely populated communities containing
thousands of galactic residents, called galaxy clusters.
"Previously, we only knew of a handful of galaxy clusters that
existed when our universe was in its first few billion years. Now,
thanks to Spitzer's superb sensitivity, we've identified over a
hundred," says Dr. Mark Brodwin, of the National Optical Astronomy
Observatory, in Tucson, Ariz.
Using Spitzer's substantial sample of distant galaxy clusters,
Brodwin and his colleagues were able to conduct a statistical
analysis showing that distant galaxy clusters tend to huddle together
-- like cosmic urban sprawl with neighborhoods growing together into
a larger and larger community.
"The clustering of clusters indicates that these ancient galactic
cities are not randomly distributed across space," says Brodwin.
Astronomers have long suspected that the first galaxy clusters grew
in very special regions of space, where pockets of hot gas began
collecting hundreds of thousands of years after the big bang. The
fact that ancient galaxy clusters clump together could be evidence
that they formed in such dense regions in the early universe.
Brodwin notes that this observed clumping matches current
astronomical theories about galaxy cluster formation. Theory
predicted the density of these cosmic cities in the distant past, and
the recent measurements of his team have confirmed these predictions.
"This analysis is helping us understand how the largest structures in
the universe came to be," says Brodwin.
Brodwin's paper was published in the December 20, 2007 issue of
Astrophysical Journal Letters. Co-authors on this paper are Leonidas
Moustakas, Peter Eisenhardt, and Daniel Stern, of NASA's Jet
Propulsion Laboratory in Pasadena, Calif.; Anthony Gonzalez, of the
University of Florida, Gainsville, Fla.; Adam Stanford, of the
University of California at Santa Cruz; and Michael Brown of Monash
University in Clayton, Australia.
COSMIC SEARCHLIGHTS REVEAL "LOST" GALAXIES
Millions of faint galaxies are hovering near the edge of our
universe, too dim to be detected by most telescopes -- but some huge
cosmic explosions and the supersensitive infrared eyes of NASA's
Spitzer Space Telescope are bringing many of these muted galaxies to
Located approximately 12.5 billion light-years away from Earth, the
distant galaxies exist in an era when our universe was just one
billion years old. With Spitzer's sensitive infrared eyes,
astronomers can finally snap infrared portraits and even "weigh" many
of these otherwise invisible galaxies.
"A few billion years after the big bang, 90 percent of the stars
being born were occurring in these types of faint galaxies. By
identifying this population, we hope to gain insights into the
environments where the universe's first stars formed," says Dr. Ranga
Ram Chary, of the Spitzer Science Center, Pasadena, Calif.
Finding Hidden Galaxies
How did astronomers find these elusive galaxies? Like a searchlight
directing people to a high-profile event, astronomers followed an
afterglow from huge explosions, called "gamma ray bursts" to the
faint distant galaxies. They suspect that gamma ray bursts appear
when a very massive star dies and becomes a black hole.
Gamma ray bursts are fleeting events -- lasting anywhere from a
fraction of a second, to a few minutes. This is not enough time for
astronomers to directly identify their source. However, as the gamma
ray light fades, a lingering afterglow can be seen at other
wavelengths of light. In fact, Chary's team used ground-based
telescopes to follow the infrared afterglow from several of these
events back to their dim host galaxies, months after the initial
The afterglow occurs when energetic electrons spiral around magnetic
fields, and release light. In its explosive death, material shooting
out of the massive star smashes into surrounding gas. This violent
collision heats nearby gas and energizes its electrons.
Once coordinates of the faint galaxies were determined, Chary's team
then used Spitzer's supersensitive infrared array camera to snap a
picture of the faint galaxy. The amount of light from the galaxies
allowed Chary to weigh the galaxies. They found these distant
galaxies were cosmic "lightweights", or not very massive compared to
mature galaxies we see nearby.
"Understanding the mass and chemical makeup of the universe's first
galaxies and then taking snapshots of galaxies at different ages,
gives us a better idea of how gas, dust and metals-- the material
that went into making our Sun, solar system, and Earth --has changed
throughout the Universe's history," says Chary.
Unlike the galaxies of today, Chary says that galaxies living in the
one billion year old universe were much more pristine -- comprised
primarily of hydrogen and helium gas and containing less than 10% of
the heavier elements we see in the local Universe, and even on Earth.
The stars that formed and lived in these galaxies eventually forged
heavier chemical elements in their cores. In death, the stars spit
their chemical creations into space. Some of that material went into
making another generation of stars and eventually planets in the
galaxies while a fraction of the metals were ejected entirely out of
Chary's paper was published in the December 10, 2007 issue of the
Astrophysical Journal. Co-authors on this paper include Dr. Edo
Berger, of Princeton University, Princeton, NJ, and Dr. Len Cowie, of
the University of Hawaii.
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