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Wednesday, October 8, 2008


NASA's "Great Observatories" have teamed up with other telescopes on Earth and in space to produce glorious pictures showing how stars are born.

Astronomers believe the first generations of stars were crushed into existence as cosmic gas congealed into galaxies, and that's the focus of a clever study that draws upon the Hubble Space Telescope's view of a bizarre "Cosmic Eye." More recently, blasts of radiation and supernova winds are hammering out stars from clouds of gas and dust, as seen in a pair of pictures that incorporate data from the Spitzer Space Telescope.

Here's a quick guide to the latest fireworks displays from NASA's three Great Observatories: Hubble, Spitzer and the Chandra X-Ray Observatory:

Stellar work of art
The picture below shows NGC 346, a star-forming cloud that is 210,000 light-years away in the Small Magellanic Cloud, a satellite dwarf galaxy orbiting our own Milky Way. The carnival colors reflect a spectrum of light that is far wider than the human eye can perceive - and that's the secret to interpreting what's happening.

"NGC 346 is an astronomical zoo," Dimitrios Gouliermis of Germany's Max Planck Institute for Astronomy explained in today's image advisory. "When we combined data from various wavelengths, we were able to tease apart what's going in in different parts of the cloud."

NASA / JPL-Caltech / XMM / NTT / MPIA
This painterly portrait of a star-forming cloud called
NGC 346 combines imagery from several telescopes.
Click on the picture to see a bigger version.

Clouds of cold dust show up best in the infrared wavelengths that are Spitzer's specialty. In this picture, they show up as red blotches. The green areas represent glowing gas, as seen in visible wavelengths by the European Southern Observatory's New Technology Telescope. Even hotter gas has been detected in X-ray wavelengths by the European Space Agency's XMM-Newton space telescope, and that gas is portrayed as a blue haze.

Ordinary stars appear as blue spots with white centers, while young, dust-enshrouded stars appear as pinkish-red spots with white centers.

The bright area at the center of the picture represents a region that is being blasted with radiation from massive stars. The resulting shock waves are squeezing new stars into existence.

Higher up in the cloud and toward the left, you can see a bright spot surrounded by a bluish glow. The glow is actually created by winds given off by a supernova explosion 50,000 years ago. The bright spot isn't the star that blew up - it's actually a triple-team of stars shining through the winds. The supernova winds push against the cloud of gas and dust seen to the right, spawning infant stars (which look pretty in pink).

The results show that two mechanisms for star formation can be at work simultaneously in the same region. The international team's findings are due to be published in an upcoming issue of the Astrophysical Journal. Check the Spitzer Web site and this Caltech news release as well as the ESA Web site and the ESO Web site for further explanation.

Hidden star clusters
Scientists combined infrared observations from Spitzer with X-ray observations from Chandra to figure out how stars were being born inside clouds of dust so thick that you can't see them in visible light.

NASA / JPL-Caltech / CXO / CfA
RCW 108 is a region where stars are forming within
the Milky Way, about 4,000 light-years from Earth. Click on the picture to see a larger version.

RCW 108 is a star-forming region in our own Milky Way galaxy, 4,000 light-years from Earth in the southern constellation Ara. This picture of the region is a composite, with Spitzer's infrared view highlighted in red and orange and Chandra's view shown in blue.

Chandra identified hundreds of hot, massive stars that are giving off violent bursts of radiation, including members a large star cluster known as NGC 6193 that is visible on the left side of the image. Astronomers believe that the radiation given off by these hot stars is carving away at the thick clouds of dust and gas that Spitzer mapped in detail.

The blast of radiation appears to have sparked the birth of a new star cluster inside the knot of clouds near the center of the image. The stars themselves are so thickly shrouded that their X-ray emissions can't be seen.

Click on over to the Spitzer Web site and the Chandra Web site for more about RCW 108.

The Cosmic Eye
The last region in our star-forming trio is a galaxy far, far, far away - about 11 billion light-years away, in fact, close to the edge of the observable universe. In this week's issue of the journal Nature, astronomers from the U.S. and Britain describe how they got a closer view of the galaxy by using the Hubble Space Telescope plus a galactic gravitational lens.

"Gravity has effectively provided us with an additional zoom lens, enabling us to study this distant galaxy on scales approaching only a few hundred light years," Caltech's Dan Stark, the research team's leader, said in a statement from Durham University. "This is ten times finer sampling than previously."

NASA / ESA / STScI via Durham U.
A Hubble Space Telescope image shows the "Cosmic
Eye." The yellow source in the middle is the
foreground lensing galaxy, while the blue ring is the
lensed image of the background star-forming galaxy.

The "zoom lens" is a galaxy that is sitting smack-dab between us and the distant galaxy, 2.2 billion light-years away. Because of the alignment, and because of general relativity, the nearer galaxy's gravitational field bends and focuses light beams from the faraway source. That produces what's known as a partial Einstein ring, nicknamed "the Cosmic Eye."

Stark and his colleagues analyzed the spectral signature from that focused light, and found that there was a subtle redshift effect: One edge of the faraway galaxy is moving away from us, and the other is moving toward us. That led the researchers to conclude that the galaxy is in a whirl.

"For the first time we can see that a typical-sized young galaxy is spinning and slowly evolving into a spiral galaxy much like our own Milky Way," Stark said.

The researchers also factored in data from the Keck Observatory in Hawaii and the Plateau de Bure Interferometer in the French Alps. The interferometer's millimeter-wave instrument is sensitive to the distribution of cold gas that collapses to form stars.

"Remarkably, the cold gas traced by our millimeter observations shares the rotation shown by the young stars in the Keck observations," said study co-author Mark Swinbank of Durham University's Institute for Computational Cosmology. "The distribution of gas seen with our amazing resolution indicates we are witnessing the gradual buildup of a spiral disk with a central nuclear component."

The bottom line is that the far, faraway galaxy is apparently being formed from scratch, rather than through the collision of pre-existing galaxies. As all that cold primordial gas swirls together, it collapses gravitationally into a first generation of stars - a process that has not been seen in such detail before.

"Effectively, we are looking back in time to when the universe was in its very early stages," Swinbank said. "This technique of using gravitational lensing provides us with a glimpse of what we will commonly achieve when the next generation of telescopes, which are still a decade away, come online."

To get a preview of the Atacama Large Millimeter Array and other monster observatories, check out our interactive gallery of next-generation telescopes, as well as the Web sites for ALMA, the E-ELT and the TMT.

The NGC 346 study's authors include Gouliermis as well as Thomas Henning, Wolfgang Brandner, Eva Hennekemper and Felix Hormuth of the Max Planck Institute for Astronomy, and You-Hua Chu and Robert Gruendl of the University of Illinois at Urbana-Champaign. The "Cosmic Eye" study's authors include Stark and Swinbank as well as Richard Ellis and Johan Richard of Caltech, Simon Dye of Cardiff University and Ian Smail of Durham University.

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