[Spitzer-news] NASA's Spitzer Peels Back Layers of Star's Explosion
PLUS Snake on a Galactic Plane!
spitzer-news at lists.ipac.caltech.edu
spitzer-news at lists.ipac.caltech.edu
Fri Oct 27 18:56:46 PDT 2006
In this issue:
1) NASA's Spitzer Peels Back Layers of Star's Explosion
2) Snake on a Galactic Plane!
3) Belching Black Holes
4) C2D: Before Planets and Life, There Are Stars and Disks
5) 'Art of Astronomy' Event To Feature Space Artists and More
NASA'S SPITZER PEELS BACK LAYERS OF STAR'S EXPLOSION
Astronomers using NASA's infrared Spitzer Space Telescope have
discovered that an exploded star, named Cassiopeia A, blew up in a
somewhat orderly fashion, retaining much of its original onion-like
"Spitzer has essentially found key missing pieces of the Cassiopeia A
puzzle," said Jessica Ennis of the University of Minnesota, Minneapolis,
lead author of a paper to appear in the Nov. 20 issue of the
"We've found new bits of the 'onion' layers that had not been seen
before," said Dr. Lawrence Rudnick, also of the University of Minnesota,
and principal investigator of the research. "This tells us that the
star's explosion was not chaotic enough to stir its remains into one big
pile of mush."
Cassiopeia A, or Cas A for short, is what is known as a supernova
remnant. The original star, about 15 to 20 times more massive than our
sun, died in a cataclysmic "supernova" explosion relatively recently in
our own Milky Way galaxy. Like all mature massive stars, the Cas A star
was once neat and tidy, consisting of concentric shells made up of
various elements. The star's outer skin consisted of lighter elements,
such as hydrogen; its middle layers were lined with heavier elements
like neon; and its core was stacked with the heaviest elements, such as
Until now, scientists were not exactly sure what happened to the Cas A
star when it ripped apart. One possibility is that the star exploded in
a more or less uniform fashion, flinging its layers out in successive
order. If this were the case, then those layers should be preserved in
the expanding debris. Previous observations revealed portions of some of
these layers, but there were mysterious gaps.
Spitzer was able to solve the riddle. It turns out that parts of the Cas
A star had not been shot out as fast as others when the star exploded.
Imagine an onion blasting apart with some layered chunks cracking off
and zooming away, and other chunks from a different part of the onion
shooting off at slightly slower speeds.
"Now we can better reconstruct how the star exploded," said Dr. William
Reach of NASA's Spitzer Science Center, Pasadena, Calif. "It seems that
most of the star's original layers flew outward in successive order, but
at different average speeds depending on where they started."
How did Spitzer find the missing puzzle pieces? As the star's layers
whiz outward, they are ramming, one by one, into a shock wave from the
explosion and heating up. Material that hit the shock wave sooner has
had more time to heat up to temperatures that radiate X-ray and visible
light. Material that is just now hitting the shock wave is cooler and
glowing with infrared light. Consequently, previous X-ray and
visible-light observations identified hot, deep-layer material that had
been flung out quickly, but not the cooler missing chunks that lagged
behind. Spitzer's infrared detectors were able to find the missing
chunks - gas and dust consisting of the middle-layer elements neon,
oxygen and aluminum.
Cassiopeia A is the ideal target for studying the anatomy of a supernova
explosion. Because it is young and relatively close to our solar system,
it is undergoing its final death throes right in front of the watchful
eyes of various telescopes. In a few hundred years or so, Cas A's
scattered remains will have completely mixed together, forever erasing
important clues about how the star lived and died.
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.
For more information about Spitzer, visit
SNAKE ON A GALACTIC PLANE!
Something scary appears to be slithering across the plane of our Milky
Way galaxy in a new Halloween image from NASA's Spitzer Space Telescope.
The snake-like object is actually the core of a thick, sooty cloud large
enough to swallow dozens of solar systems. In fact, astronomers say its
"belly" may be harboring beastly stars in the process of forming.
The image can be viewed at
"The snake is an ideal place to hunt for massive forming stars as they
have not had time to heat up and destroy the cloud they are born in,"
said Dr. Sean Carey, also known as "Dr. Scarey," of NASA's Spitzer
Science Center. Dr. Scarey, who is leading the new research, was also
principal investigator of a previous Halloween image from Spitzer,
showing a "great galactic ghoul" (
Spitzer was able to spot the sinuous cloud using its heat-seeking
infrared vision. The object is hiding in the dusty plane of our Milky
Way galaxy, invisible to optical telescopes. Because its heat, or
infrared light, can sneak through the dust, it first showed up in
infrared images from past missions. The cloud is so thick with dust that
if you were to somehow transport yourself into the middle of it, you
would see nothing but black, not even a star in the sky. Now, that's
Spitzer's new view of the snake provides the best look at what lurks
inside. The yellow and orange spots located on and around it are massive
stars just beginning to take shape. The bright red spot located on its
belly is a monstrous stellar embryo, with about 20 to 50 times the mass
of our sun.
Astronomers say these observations will ultimately help them better
understand how massive stars form. By studying the clustering and range
of masses of the stellar embryos, they hope to determine if the stars
were born in the same way that our low-mass sun was formed - out of a
collapsing cloud of gas and dust - or by another mechanism in which the
environment plays a larger role.
The snake is located about 11,000 light-years away in the constellation
BELCHING BLACK HOLES
Astronomers using NASA's Spitzer Space Telescope have recently
identified two quasars, or supermassive black holes, that may be on the
verge of a colossal cosmic "belch."
Scientists have long suspected that when galaxies collide, the
supermassive black holes that reside within them gorge on a magnificent
"buffet" of dust, gas, and stars. The cosmic feast is provided by
violent episodes of star formation triggered in the great galactic
clash. Most telescopes cannot detect these feasting black holes because
dense clouds of dust and gas kicked up in the galactic collision shroud
the objects from view.
However, at some point astronomers suspect that these celestial gluttons
do get "full." Once this happens, scientists believe that the black
holes let out an enormous belch of energy, strong enough to destroy much
of its obscuring surrounding material. Some supermassive black hole
belches may even destroy enough material to stop star formation in its
According to Dr. Maria del Carmen Polletta of the University of
California at San Diego, in La Jolla, Calif., the recently identified
supermassive black holes are heavily cloaked in dense dust clouds, and
may be on the verge of such a cosmic burp. Polletta is the lead author
of a paper on the topic. Her research was published in the May 2006
issue of Astrophysical Journal.
"Black holes always release a lot of energy as they accrete [or gobble
up] matter," she says.
As matter falls into a black hole, energy is emitted. The more a black
hole eats, the more energy is released. Astronomers suspect that at some
point black holes will emit so much energy that the surrounding dust
will be blown away or destroyed. Scientists measure this emitted energy
in "luminosity." Polletta notes that the most luminous black hole in her
study is about three billion times more massive than our Sun, and can
gobble up about 68 solar masses of material per year, or more than the
mass of one Sun per week.
"The dust surrounding an obscured black hole can complicate calculations
of luminosity because dust actually absorbs some of the emitted energy
and reradiates it in the infrared," says Polletta.
Using Spitzer's infrared eyes, Polletta and her team were able to
measure the amount of energy being absorbed by dust, and thus accurately
predict the black hole's luminosity. With NASA's Chandra X-ray
Observatory, team members were also able to discern the amount of dust
surrounding the object.
"The luminosity of the sources in my research are so high that dust
should not survive," says Polletta. This is why she suspects that the
black holes in her study are about to belch.
Although this type of phenomena has been predicted in astronomical
models, Polletta is careful to note that there is still a lot that
astronomers don't know about character of heavily obscured black holes.
"Black holes that are this heavily obscured and with this luminosity are
very difficult to find and have not been extensively studied," says
Polletta. "The belch of a black hole has never been verified with
observations, so the explosion may not happen."
"The role that supermassive black holes play in the development of a
galaxy is still unclear, there are still a lot of missing pieces. What
we are seeing here is a very specific moment in the life of a black
hole," she adds. "According to astronomical models, black holes at this
luminosity should destroy their surrounding material pretty soon."
The sources were detected in observations obtained by the Spitzer Wide
area Infrared Extragalactic (SWIRE) Legacy project. The SWIRE Legacy
project uses Spitzer's super sensitive infrared eyes to understand how
material from the big bang developed into our modern galactic neighbors.
According to Polletta, who is a member of the SWIRE team, out of the
millions of supermassive black holes detected by SWIRE, the objects in
her study are the most luminous. She adds that her sources are among the
most dust-obscured black holes ever studied.
C2D: BEFORE PLANETS AND LIFE, THERE ARE STARS AND DISKS
What would a universe without stars look like?
Besides cold and dark, it would also look relatively empty and lifeless,
as chemical elements like carbon, nitrogen, oxygen, and most others
which are necessary to create planets and sustain life wouldn't exist.
Almost all chemical elements other than hydrogen and helium are born
inside stars and spread across the universe when stars die.
Despite their importance, much about the birth and early life of stars
remains a mystery. That's why a team of astronomers on a Spitzer Legacy
project called "From Molecular Cores to Planet-Forming Disks,"
abbreviated "c2d," are pointing all three instruments aboard NASA's
Spitzer Space Telescope toward young stars forming in a variety of
nearby cosmic clouds.
"The main goal of our project is to study the nature of star formation
and the beginnings of planet formation," said Dr. Neal Evans, principal
investigator of the c2d project.
Seeking Invisible Stars
Before c2d astronomers can learn about the birth and early life of
stars, they must first identify a sample to study. Since star formation
is an extremely dusty process, some astronomers note that recognizing
infant stars may be easier said than done.
Stars are born from the collapse of dense gas and dust patches deep
inside a cosmic cloud. For much of their early life, stars are visibly
hidden behind the dust that created them. Although astronomers cannot
see infant stars, they can detect their heat with infrared telescopes
According to c2d co-investigator Dr. Lori Allen, identifying baby stars
in a large cosmic cloud is very similar to looking down on the Earth at
night and searching for small mid-western towns.
"When you're looking down on the Earth at night, big cities like Los
Angeles and New York are easy to spot because their city lights are
bright and concentrated, whereas small town lights are not, so they are
harder to find," says Allen.
"When you are looking at a star-forming cloud, it is very much the same.
The areas that contain large concentrations of stars are easier to see
and study," she adds.
Allen notes that past infrared telescopes like, the Infrared
Astronomical Satellite (IRAS), could map the entire sky but were only
sensitive enough to see the "large cities" of stars. With the launch of
Spitzer (the most sensitive infrared telescope ever flown) astronomers
can see the "small towns," or regions were faint baby stars are just
beginning to form.
"Thanks to Spitzer's superb sensitivity, we've greatly increased the
number of young known stars in some of these clouds," says Evans.
Spitzer Studies Stellar and Planetary Beginnings
Once a small town of infant stars is identified, astronomers can gather
details about how stars grow and develop by combining observations from
all three instruments aboard Spitzer.
Currently astronomers do not know how a dense cloud patch collapses to
form a star, how a baby star develops, or what initiates planet
formation around a star. Because stars and planets form over thousands
(sometimes millions) of years, scientists cannot learn about their
formation by watching a single star or planet grow. Instead, they have
to piece together the story of stellar and planetary development by
taking snapshots of a variety of stars and planets at different life
stages. In other words, by comparing an image of an "embryonic" star, an
"infant" star, and a "toddler" star, astronomers can discern details
about the "childhood" of all stars.
C2D team members obtain images of "stellar embryos" using Spitzer's
Multiband Imaging Photometer (MIPS) instrument. In this development
stage, the dense cloud patch is collapsing to form a star, and the
embryonic orb is not massive enough to "light up" visibly by igniting
nuclear fusion in its core. Visible-light telescopes and instruments
cannot see a star in this phase, but Spitzer's MIPS instrument can. As
the dense cloud patch collapses, it heats up slightly. MIPS' sensitive
far-infrared eyes can detect this heat, allowing the instrument to
capture never before seen pictures of stellar embryos.
Pictures of "stellar infants" are captured with Spitzer's Infrared Array
Camera (IRAC). Stars in this stage are obscured from visible-light view
by the cloud of gas and dust that created them. Eventually, some stars
will develop winds strong enough to blow away their surrounding natal
material and reveal themselves to the universe. Meanwhile, other stars
will turn this birth material into planet-forming disks, astronomically
known as "protoplanetary disks." Team members studying the early stages
of planet formation also use IRAC to look at protoplanetary disks.
To gather insights into the environments where stellar embryos are
forming, stellar infants are growing, and planets are developing, c2d
astronomers turn to Spitzer's Infrared Spectrograph (IRS) instrument.
According to Evans, IRS allows scientists to detect how much dust, ice,
and other materials are present in the region. He notes that the
instrument's superb sensitivity even allows astronomers to determine the
kind of ice that is coating the dust grain, whether its carbon,
hydrogen, nitrogen, or oxygen rich ice.
"Knowing that dust grains in a protoplanetary disk are coated with ice
rich in molecules containing hydrogen, oxygen, carbon, and nitrogen,
could be influential in helping us determine whether planets like Earth
are common in the universe," said Evans. "All of these molecules are
also necessary for the origin of life."
According to Allen, c2d's legacy to future astronomers lies in its
unprecedented detailed infrared maps of approximately 100 dense
star-forming regions, and five large nearby cosmic clouds, each located
less than 1,000 light-years away.
In space, clouds absorb visible starlight from all the stars behind and
inside of it. Thus, through a visible-light telescope lens, cosmic
clouds look like big, dark, featureless blobs. With sensitive
dust-piercing infrared telescopes like Spitzer, astronomers can see the
heat emanating from stars inside and behind the cloud.
"While the great sensitivity of Spitzer allows c2d to find all the young
objects in a cloud, it also captures background star-forming galaxies
beyond the Milky Way," said Evans. "Because galaxies are so far away,
they look like dots in our data and can be confused with stars. We
actually spent a lot of time trying to weed galaxies out of our sample."
Similar to the way IRAS all-sky maps helped to point Spitzer in the
direction of "small stellar towns," Allen notes that c2d maps created
with Spitzer will point future, more sensitive infrared missions like
the Herschel Space Observatory and the James Webb Space Telescope in the
right direction, so that they may gain deeper insights into the early
development of stars.
"Our maps may even help direct the Terrestrial Planet Finder mission
toward terrestrial planets in other solar systems," she adds.
"My hope is for future astronomers to use our data in ways that we never
thought possible," said Evans.
'ART OF ASTRONOMY' EVENT TO FEATURE SPACE ARTISTS AND MORE
Mark your calendars for The Art of Astronomy, a three-day public event
celebrating the collaboration of astronomy and art in Pasadena,
California. The event will feature a spectacular slide show of cosmic
images, lectures from world-renowned space artists, and a public
unveiling of a magnificent new image from NASA's Spitzer and Hubble
The Art of Astronomy kicks off on Saturday, November 4, 2006, with a
slide show of cosmic images, which will run continuously every evening
through the weekend. Showings will begin at dusk and end at 11pm in the
One Colorado Courtyard (between Colorado Blvd. and Union St. and between
Fair Oaks and DeLacey) in Old Pasadena.
The event will culminate with space art lectures and a public image
unveiling at 7:30 pm on Monday, November 6, in the One Colorado
The Art of Astronomy is a public event sponsored by the Spitzer Science
Center's Astro Viz 2006 Workshop, a meeting of international space
artists dedicated to expanding the field of astronomy visualization. The
Spitzer Science Center at the California Institute of Technology,
Pasadena, is the science operations headquarters for NASA's Spitzer
Space Telescope mission, which explores the cosmos in infrared light.
NASA's Jet Propulsions Laboratory, also located in Pasadena, manages the
Spitzer Space Telescope mission for NASA's Science Mission Directorate,
One Colorado is an outdoor shopping, dining, and entertainment district
spanning one city block in Old Pasadena. This award-winning destination
unites the urban environment of 17 historic buildings with 40
contemporary fashion and dining attractions. The One Colorado Courtyard,
designed in the tradition of European town squares, is Old Pasadena's
main public space for film festivals, live music, high-quality fine art
markets, children's programs, and site-specific art installations
curated by the Armory Center for the Arts.
More information about the Spitzer-news