[Spitzer-news] Planet-Forming Disks Might Put the Brakes on Stars

spitzer-news at lists.ipac.caltech.edu spitzer-news at lists.ipac.caltech.edu
Mon Jul 24 09:58:59 PDT 2006

In this issue:

1) Planet-Forming Disks Might Put the Brakes on Stars 
2) The Infrared Universe Comes to the Los Angeles County Arboretum 
3) Black Hole Spills Kaleidoscope of Color 
4) Spitzer Spots Building Blocks of Life in Supernova Remnant 
5) Astronomer in the Making 
6) How To Bake a Galaxy



Astronomers using NASA's Spitzer Space Telescope have found evidence
that dusty disks of planet-forming material tug on and slow down the
young, whirling stars they surround.

Young stars are full of energy, spinning around like tops in half a day
or less. They would spin even faster, but something puts on the brakes.
While scientists had theorized that planet-forming disks might be at
least part of the answer, demonstrating this had been hard to do until

"We knew that something must be keeping the stars' speed in check," said
Dr. Luisa Rebull of NASA's Spitzer Science Center, Pasadena, Calif.
"Disks were the most logical answer, but we had to wait for Spitzer to
see the disks." 

Rebull, who has been working on the problem for nearly a decade, is lead
author of a new paper in the July 20 issue of the Astrophysical Journal.
The findings are part of a quest to understand the complex relationship
between young stars and their burgeoning planetary systems. 

Stars begin life as collapsing balls of gas that spin faster and faster
as they shrink, like twirling ice skaters pulling in their arms. As the
stars whip around, excess gas and dust flatten into surrounding
pancake-like disks. The dust and gas in the disks are believed to
eventually clump together to form planets.

Developing stars spin so fast that, left unchecked, they would never
fully contract and become stars. Prior to the new study, astronomers had
theorized that disks might be slowing the super speedy stars by yanking
on their magnetic fields. When a star's fields pass through a disk, they
are thought to get bogged down like a spoon in molasses. This locks a
star's rotation to the slower-turning disk, so the shrinking star can't
spin faster.

To prove this principle, Rebull and her team turned to Spitzer for help.
Launched in August of 2003, the infrared observatory is an expert at
finding the swirling disks around stars, because dust in the disks is
heated by starlight and glows at infrared wavelengths. 

The team used Spitzer to observe nearly 500 young stars in the Orion
nebula. They divided the stars into slow spinners and fast spinners, and
determined that the slow spinners are five times more likely to have
disks than the fast ones.

"We can now say that disks play some kind of role in slowing down stars
in at least one region, but there could be a host of other factors
operating in tandem. And stars might behave differently in different
environments," Rebull said. 

Other factors that contribute to a star's winding down over longer
periods of time include stellar winds and possibly full-grown planets.

If planet-forming disks slow down stars, does that mean stars with
planets spin more slowly than stars without planets? Not necessarily,
according to Rebull, who said slowly spinning stars might simply take
more time than other stars to clear their disks and develop planets.
Such late-blooming stars would, in effect, give their disks more time to
put on the brakes and slow them down.

Ultimately, the question of how a star's rotation rate is related to its
ability to support planets will fall to planet hunters. So far, all
known planets in the universe circle stars that turn around lazily. Our
sun is considered a slowpoke, currently plodding along at a rate of one
revolution every 28 days. And, due to limits in technology, planet
hunters have not been able to find any extrasolar planets around zippy

"We'll have to use different tools for detecting planets around rapidly
spinning stars, such as next-generation ground and space telescopes,"
said Dr. Steve Strom, an astronomer at the National Optical Astronomy
Observatory, Tucson, Ariz.

Other members of Rebull's team include Drs. John Stauffer of the Spitzer
Science Center; S. Thomas Megeath at the University of Toledo, Ohio; and
Joseph Hora and Lee Hartmann of the Harvard-Smithsonian Center for
Astrophysics, Cambridge, Mass. Hartmann is also affiliated with the
University of Michigan, Ann Arbor.

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. Caltech manages JPL
for NASA.

For an animation depicting how disks slow stars and more information
about Spitzer, visit www.spitzer.caltech.edu/spitzer .




Want to lift off into space, but don't have a rocket? Just stop by the
Los Angeles County Arboretum & Botanic Garden on July 30, 2006, from 5
pm to 10 pm, and the Spitzer Science Center will bring the infrared
universe to you! 

The Arboretum is hosting a unique celebration of nature, technology and
art, titled "Terra-Byte" (terra as in the planet Earth, and byte
describing a unit of storage in computers). The celebration will include
a dazzling display of cosmic images and artist's concepts from NASA's
Spitzer Space Telescope. Astronomer, space artist, and host of the
popular Hidden Universe vodcast, Dr. Robert Hurt, will be available to
answer questions about space, and demonstrate how infrared technology

Guests can also make their way through an evening of ever-changing
sounds, sights and spaces within the "Ephemeral Forest," an outdoor
tensile, structural composition of bamboo and fabric designed on-site.
In addition, there will be "soundscape" performances and a disc jockey
music set accompanied by visuals. 

The event is free with a cash bar, food and hands-on activities. Walking
garden tours are offered before dark. 

The Arboretum is located at 301 N. Baldwin Avenue in Arcadia,
California, just 2 miles east of Pasadena. 

For more information please visit: www.arboretum.org. 




Shoes may not come in every color, but space objects do. All objects in
space, everything from dust to distant galaxies, give off a rainbow of
light -- including light our eyes can't see. That's where NASA's Great
Observatories come in. Together, they help astronomers see all the
shades of the cosmos. 

A new false-colored image from NASA's Hubble, Chandra, and Spitzer space
telescopes demonstrates this principle beautifully. The multi-hued
portrait shows a giant jet of particles that has been shot out from the
vicinity of a type of supermassive black hole called a quasar. The jet
is enormous, stretching across more than 100,000 light-years of space --
a size comparable to our own Milky Way galaxy! 

Quasars are among the brightest objects in the universe. They consist of
supermassive black holes surrounded by turbulent material, which is
being heated up as it is dragged toward the black hole. This hot
material glows brilliantly, and some of it gets blown off into space in
the form of powerful jets. 

The jet pictured here is streaming out from the first known quasar,
called 3C273, discovered in 1963. A kaleidoscope of colors represents
the jet's assorted light waves. X-rays, the highest-energy light in the
image, are shown at the far left in blue (the black hole itself is well
to the left of the image). The X-rays were captured by Chandra. As you
move from left to right, the light diminishes in energy, and wavelengths
increase in size. Visible light recorded by Hubble is displayed in
green, while infrared light caught by Spitzer is red. Areas where
visible and infrared light overlap appear yellow. 

Astronomers were able to use these data to solve the mystery of how
light is produced is quasar jets. Light is created in a few, very
different ways. For example, our sun generates most of its light via a
process called fusion, in which hydrogen atoms are combined, causing an
explosion of light. In the case of this jet, even the most energetic
light was unexpectedly found to be the result of charged particles
spiraling through a magnetic field, a process known as synchrotron




In 1987 a massive star exploded in a neighboring galaxy, an event called
a supernova. It was the closest supernova to Earth since the invention
of the telescope centuries ago. Now, a team using the Spitzer Space
Telescope and the 8-meter Gemini South infrared telescope in Chile have
probed the supernova remnant and found the building blocks of rocky
planets and all living creatures. 

"Supernova 1987A is changing right before our eyes," said Dr. Eli Dwek,
a cosmic dust expert at NASA Goddard Space Flight Center in Greenbelt,
Md. For several years Dwek has been following this supernova, named
1987A for the year it was discovered in the Large Magellanic Cloud, a
neighboring dwarf galaxy. "What we are seeing now is a milestone in the
evolution of a supernova." 

Using infrared telescopes, Dwek and his colleagues detected silicate
dust created by the star from before it exploded. This dust survived the
intense radiation from the explosion. Nearly 20 years onward, the
supernova shock wave blasting through the debris that was shed by the
star prior to its fiery death is now sweeping up this dust, making the
material "visible" to infrared detectors. 

Dust -- chemical particles and crystals finer than beach sand -- is both
a frustration and a fascination for astronomers. Dust can obscure
observations of distant stars. Yet dust is the stuff from which all
solid bodies are formed. This is why dust research, as bland as it
sounds, is one of the most important topics in astronomy and

Dust is made in stars and hurled into space by stellar winds and
supernovae, and it is found everywhere in the universe. But little is
known about its origin and the processes that affect it. How much dust
is made in a star? How much survives the star explosion and subsequent
journey through interstellar space? And how do wispy dust clouds form
planets and ultimately life? 

These are the questions that scientists such as Eli Dwek and his
colleague Dr. Patrice Bouchet of the Observatoire de Paris want to
answer. With 1987A, they have a perfect laboratory to watch the process

This is new territory for astronomers, said Bouchet, whose research team
made infrared observations of SN 1987A with the Gemini South telescope
in Chile. Bouchet's team is witnessing processes never before seen. This
is the first time scientists have direct evidence of dust from a large
star surviving a supernova; the first time they detect cold dust
intermingled in hot, X-ray-emitting gas of millions of degrees; and the
first time they are witnessing sputtering, the process in which dust is
eroded by collisions with hot gas. 

They frankly don't know what to expect, and they have already stumbled
upon a few surprises. 

Infrared telescopes are crucial for this kind of observation. The dust
is over a hundred degrees below the freezing point of water and too cold
to emit visible light. Infrared is a less-energetic form of radiation
than visible light. So while optical telescopes like Hubble can see gas,
infrared instruments, similar to night-vision goggles, are needed to see
the cold, dark dust. 

Through high-resolution infrared imaging with the 8-meter Gemini South
telescope, the science team determined that the dust is in the region of
the equatorial ring of gas around SN 1987A. This ring of gas and dust,
about a light year across, is expanding only very slowly. This suggests
that the ring was shed by the star about 600,000 years before it
exploded, and that the dust in the ring was formed in the stellar wind
and not in the following supernova explosion. 

The blast wave from the star's explosion has now caught up with the
ring. The collision has shocked the gas and raised the gas temperature
to 10 million degrees, which heats the dust, causing it to glow at
infrared wavelengths. 

"This much was expected," said Bouchet. "The collision between the
ejecta of Supernova 1987A and the equatorial ring was predicted to occur
sometime in the interval of 1995 to 2007, and it is now underway." 

With the location of the dust determined, the scientists used the fine
eye of NASA's Spitzer Space Telescope to determine the composition of
the dust. To their great surprise, the dust was pure silicate particles. 

Another key finding is that the team has detected far less dust than
expected. A star as massive as the one that blew apart in SN 1987A
likely produced more silicate dust in the years before the supernova.
The under-abundance of dust detected by Spitzer and Gemini South could
mean that supernova blast waves destroy more dust than thought possible.
If confirmed, this will have broad implications for determining dust
origins throughout the universe. 

Yet this is a work in progress. "Overall, we are witnessing the
interaction of the supernova blast wave with its surrounding medium,
creating an environment that is rapidly evolving at all wavelengths,"
said Bouchet. 

For that reason scientists are planning a series of new infrared,
optical, and X-ray observations of SN 1987A with Spitzer, Hubble and
Chandra, NASA's three Great Observatories, now that the supernova has
once again become very interesting. Who knows what will be revealed once
the dust settles?




Adela Fedor has yet to receive a PhD, high school diploma, or even
finish the eighth grade, but that did not stop her from using NASA's
Spitzer Space Telescope to study a mysterious stellar species, called
"iron stars." 

In early April, the thirteen year-old student from Traverse City East
Junior High School in Traverse City, Mich., arrived at the Spitzer
Science Center (SSC) with her science teacher Lauren Chapple. As a
participant of the first ever Spitzer Space Telescope Research Program
for Teachers and Students, Chapple teamed up with five other science
teachers and developed a proposal to observe an iron star system with
the telescope's Infrared Spectrograph (IRS). Recently, Chapple invited
one of his brightest students to help him analyze the data. 

"A lot of people put limitations on middle school and junior high
students based on their own perceptions of what these kids are capable
of. As a teacher, I find that if kids don't know what they can't do,
they can do a lot," said Chapple. 

Astronomers have only identified two iron stars in the universe, and do
not know very much about them. Chapple, Fedor, and the other science
teachers are studying an iron star system called AS325, which contains
two stars that orbit each other. One is a dying star, in its "red giant"
phase of life. Meanwhile, its stellar companion is a "B star," one of
the most massive species of stars in the universe. 

The stars were named iron stars after previous observations revealed
that there were traces of iron in the region. Astronomers now know that
the iron is being formed in the strong winds of the B star, and the
student-teacher team is hoping that Spitzer can identify other chemicals
and molecules around the star. 

"I was very impressed by how well the group handled spectroscopy. This
data is really hard to work with because you are basically looking at a
bunch of squiggly lines and trying to identify specific chemicals and
molecules," said Dr. Steve Howell of the National Optical Astronomy
Observatory (NOAO). Howell is one of the iron star project's supporting

In addition to Chapple and Fedor, the group members visiting the SSC in
early April included science teachers Steve Rapp of Linwood Holton
Governor's School in Abington, Va. and Beth Thomas of East Middle School
in Great Falls, Mont. Dr. Carolyn Brinkworth of the SSC also assisted
the team in their data analysis. 

Although Fedor says that she does not know exactly what she wants to do
when she grows up, she notes an interest in science. 

"This experience was really fun, I liked working with data and figuring
out what everything meant," said Fedor. 

The iron star team will present their findings at the January 2007
American Astronomical Society (AAS) meeting in Seattle. The research
program for teachers and students was designed by the SSC and NOAO, and
sponsored by the National Science Foundation. The program recently
started its second year, and now includes 18 participating teachers. The
second group of teachers submitted proposals for Spitzer observation
time in late 2005, attended workshops in January 2006, and will invite
students to analyze data at the SSC later this year. 




Start with lots and lots of dark matter, then stir in gas. Let the
mixture sit for a while, and a galaxy should rise up out of the batter. 

This simple recipe for baking galaxies cannot be performed at home, but
it does reflect what astronomers are learning about galaxy formation.
Like baking bread with yeast, a mysterious substance in the universe
called dark matter is required for a galaxy to grow. 

Now, a new study from NASA's Spitzer Space Telescope is refining what is
known about this essential ingredient of galaxies. It suggests that not
only is dark matter necessary, but a minimum quantity of the material
must be present before a galaxy can form. Any less would mean no galaxy
-- the cosmic equivalent of a failed loaf of bread. 

"Galaxies are born within huge clumps of dark matter," said Dr. Duncan
Farrah of Cornell University, Ithaca, N.Y. "We are finding that these
clumps seem to be remarkably consistent in size from galaxy to galaxy."
Farrah is lead author of a paper describing this and other findings in a
recent issue of Astrophysical Journal Letters. 

As its names suggests, dark matter emits no light, so no conventional
telescope can see it. So-called normal matter, which includes plants and
people and all sorts of space objects, gives off electromagnetic
radiation, or light. There is about five times more dark matter in the
universe than normal matter. 

Yet dark matter does have mass, which means that it can exert
gravitational tugs on normal matter. 

"Dark matter has gravity, so it pulls in more and more dark matter in
addition to 'normal' gas," said co-author Dr. Jason Surace of NASA's
Spitzer Science Center at the California Institute of Technology in
Pasadena. "We know that the gas eventually condenses into the stars that
make up galaxies, but the Spitzer study suggests that this doesn't
happen until the dark matter has reached a critical mass." 

Farrah and his colleagues used data from the Spitzer Wide-area Infrared
Extragalactic (SWIRE) survey to study hundreds of distant objects,
called ultraluminous infrared galaxies, located billions of light-years
away. These young galaxies are incredibly bright and filled with lots of
dusty star-formation activity. 

Initially, the researchers set out to better understand how the young
galaxies and dark matter evolve and aggregate together into the giant
clusters of mature galaxies that dominate our present-day universe. "You
might think that galaxies are just distributed randomly across the sky,
like throwing a handful of sand onto the floor," said Farrah. "But they
are not, and the reason might be that the dark matter clumps around
young galaxies are attracting each other like glue." 

By determining how tightly the ultraluminous infrared galaxies had begun
to bunch together, Farrah and his colleagues were able to indirectly
measure how much dark matter "glue" was present. The tighter the
grouping, the more dark matter there was. They did this calculation for
two batches of galaxies at varying distances from Earth. 

That's when they noticed something weird. For every galaxy they studied,
no matter how far away, there seemed to be surrounding dark matter
clumps of about the same size, the equivalent of 10 trillion solar
masses. Because the astronomers did not find any galaxies coupled with
less than 10 trillion solar masses of dark matter, they believe this
quantity must be the minimum necessary for an ultraluminous infrared
galaxy to form. 

"These dark matter clumps might be like seeds that give birth to these
distant galaxies," said Surace. "Similar galaxies in our nearby universe
form in a completely different way, so what we are learning applies to a
different epoch in our universe, far back in cosmic time." 

Whether other types of galaxies might also arise in similar ways is an
ongoing question in astronomy. Previous studies on highly energetic
galaxies called quasars have hinted that those objects also require a
minimum mass of dark matter to grow. Only in that case, the galaxies'
starting "dough" wasn't quite as dense, about four to five trillion
solar masses. 

It seems astronomers will have to wait a bit longer before the universe
gives up its best-kept family recipes. 



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