Spitzer Takes Family Portrait of Stars Amid Another “Celestal Geode”

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A new image from NASA’s Spitzer Space Telescope reveals generations of stars amid a cavity carved from a colorful cosmic cloud. The striking infrared picture shows a region, called W5, which is similar to N44F, or the “Celestial Geode” that was discussed in a Universe Today article last week. The gas cavity, which looks similar to a geode-like cavity found in some rocks, is carved by the stellar wind and intense ultraviolet radiation from hot stars. W5 is studded with stars of various ages, and provides new evidence that massive stars – through their brute winds and radiation – can trigger the birth of new stars.

The image was unveiled today at the Griffith Observatory in Los Angeles as part of Spitzer’s five-year anniversary celebration. Spitzer launched on August 25, 2003, from Cape Canaveral Air Force Station, Fla. A high-resolution version of the image is available here. It shows a family history full of life and death. But are the deaths of some stars responsible for the birth of new stars?

“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.”

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 the 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.

The astronomer who last week explained the N44F image, Dr. You-Hua Chu from the University of Illinois, said along the walls of the cavity there are dust pillars sticking out and young stars are being formed at the tips of these pillars. Similar features are seen in the new Spitzer image of W5, where younger stars (seen as pink or white in the image) are embedded in the elephant-trunk-like pillars as well, and also beyond the cavity rim. The most massive stars (seen as blue dots) are at the center of two hollow cavities.

With Spitzer’s infrared vision, Koenig and his colleagues peered through the dusty regions of W5 to get a better look at the stars’ various stages of evolution and test the triggered star formation theory. The results from their studies show 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 region, as well as other stars in the background and foreground.

A paper on the findings will appear in the December 1, 2008, issue of the Astrophysical Journal.

Source: Harvard Smithsonian Center for Astrophysics