Generations of Stars Pose for Family Portrait (Spitzer)

http://www.jpl.nasa.gov/news/news.cfm?release=2008-164

Generations of Stars Pose for Family Portrait
Jet Propulsion Laboratory
August 22, 2008

A new image from NASA's Spitzer Space Telescope tells a tale of life
and
death amidst a rich family history. The striking infrared picture
shows
a colorful cosmic cloud, called W5, studded with multiple generations
of
blazing stars.

It also provides dramatic new evidence that massive stars -- through
their brute winds and radiation -- can trigger the birth of stellar
newborns.

"Triggered star formation continues to be very hard to prove," said
Xavier Koenig of the Harvard Smithsonian Center for Astrophysics in
Cambridge, Mass. "But our preliminary analysis shows that the
phenomenon
can explain the multiple generations of stars seen in the W5 region."
Koenig is lead author of a paper about the findings in the December 1,
2008, issue of the Astrophysical Journal.

The image, which can be seen at http://www.nasa.gov/mission_pages/
spitzer/multimedia/20080722.html
<http://www.nasa.gov/mission_pages/spitzer/multimedia/20080722.html>,
is
being unveiled today at 12:30 p.m. Pacific Time at the Griffith
Observatory, Los Angeles, as part of Spitzer's five-year anniversary
celebration. Spitzer launched on August 25, 2003, from Cape Canaveral
Air Force Station, Fla.

The most massive stars in the universe form out of thick clouds of gas
and dust. The stars are so massive, ranging from 15 to about 60 times
the mass of our sun, that some of their material slides off in the
form
of winds. The scorching-hot stars also blaze with intense radiation.
Over time, both the wind and radiation blast away surrounding cloud
material, carving out expanding cavities.

Astronomers have long suspected that the carving of these cavities
causes gas to compress into successive generations of new stars. As
the
cavities grow, it is believed that more and more stars arise along the
cavities' expanding rims. The result is a radial "family tree" of
stars,
with the oldest in the middle of the cavity, and younger and younger
stars farther out.

Evidence for this theory can be seen easily in pictures of many
star-forming regions, such as W5, Orion and Carina. For example, in
the
new Spitzer picture of W5, the most massive stars (some of the blue
dots) are at the center of two hollow cavities, and younger stars
(pink
or white) are embedded in the elephant-trunk-like pillars as well as
beyond the cavity rim. However, it is possible that the younger stars
just happen to be near the edge of the cavities and were not triggered
by the massive stars.

Koenig and his colleagues set out to test the triggered star-formation
theory by studying the ages of the stars in the W5 region. They used
Spitzer's infrared vision to peer through the dusty clouds and get a
better look at the stars' various stages of evolution. They found that
stars within the W5 cavities are older than stars at the rims, and
even
older than stars farther out past the rim. This ladder-like separation
of ages provides some of the best evidence yet that massive stars do,
in
fact, give rise to younger generations.

"Our first look at this region suggests we are looking at one or two
generations of stars that were triggered by the massive stars," said
co-author Lori Allen of the Harvard-Smithsonian Center for
Astrophysics.
"We plan to follow up with even more detailed measurements of the
stars'
ages to see if there is a distinct time gap between the stars just
inside and outside the rim."

Millions of years from now, the massive stars in W5 will die in
tremendous explosions. When they do, they will destroy some of the
young
nearby stars -- the same stars they might have triggered into being.

W5 spans an area of sky equivalent to four full moons and is about
6,500
light-years away in the constellation Cassiopeia. The Spitzer picture
was taken over a period of 24 hours. The color red shows heated dust
that pervades the region's cavities. Green highlights the dense
clouds,
and white knotty areas are where the youngest of stars are forming.
The
blue dots are older stars in the star-forming cloud, as well as
unrelated stars behind and in front of the cloud.

Other authors include Robert Gutermuth, now at Smith College in
Northampton, Mass.; Chris Brunt of the University of Exeter, England;
James Muzerolle of the University of Arizona, Tucson; and Joseph Hora
of
Harvard-Smithsonian Center for Astrophysics.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the
Spitzer
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.

More information about Spitzer is at
http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer.

------------------------------------------------------------------------

Media contact: Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.b.clavin@xxxxxxxxxxxx

2008-164
.

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