….a vast stretch of cosmic clouds bubbling with new star birth. The region — a 1,000-square-degree chunk of our Milky Way galaxy — is home to numerous star-forming clouds, where massive stars have blown out bubbles in the gas and dust. “Massive stars sweep up and destroy their natal clouds, but they continuously spark new stars to form along the way,” said WISE Mission Scientist Dave Leisawitz of NASA Goddard Space Flight Center, Greenbelt, Md. Leisawitz is co-author of a new paper reporting the results in the Astrophysical Journal. “Occasionally a new, massive star forms, perpetuating the sequence of events and giving rise to the dazzling fireworks display seen in this WISE mosaic.”
The WISE space telescope mapped the entire sky two times in infrared light, completing its survey in February of 2011. Astronomers studying how stars form took advantage of WISE’s all-encompassing view by studying several star-forming clouds, or nebulae, including 10 pictured in this new view. The observations provide new evidence for a process called triggered star formation, in which the winds and sizzling radiation from massive stars compress gas and dust, inducing a second generation of stars. The same winds and radiation carve out the cavities, or bubbles, seen throughout the image.
Finding evidence for triggered star formation has proved more difficult than some might think. Astronomers are not able to watch the stars grow and evolve like biologists watching zebras in the wild. Instead, they piece together a history of star formation by looking at distinct stages in the process. It’s the equivalent of observing only baby, middle-aged and elderly zebras with crude indicators of their ages. WISE is helping to fill in these gaps by providing more and more “specimens” for study.
“Each region we looked at gave us a single snapshot of star formation in progress,” said Xavier Koenig, lead author of the new study at Goddard, who presented the results in Austin, Texas, at the 219th meeting of the American Astronomical Society. “But when we look at a whole collection of regions, we can piece together the chain of events.” After looking at several of the star-forming nebulae, Koenig and his colleagues noticed a pattern in the spatial arrangement of newborn stars. Some were found lining the blown-out cavities, a phenomenon that had been seen before, but other new stars were seen sprinkled throughout the cavity interiors.
The results suggest that stars are born in a successive fashion, one after the other, starting from a core cluster of massive stars and moving steadily outward. This lends support to the triggered star formation theory, and offers new clues about the physics of the process. The astronomers also found evidence that the bubbles seen in the star-forming clouds can spawn new bubbles. In this scenario, a massive star blasts away surrounding material, eventually triggering the birth of another star massive enough to carve out its own bubble. A few examples of what may be first- and second-generation bubbles can be seen in the new WISE image. “I can almost hear the stars pop and crackle,” said Leisawitz.
The complete WISE catalogue will be released to the public astronomy community in the spring of 2012.
This enormous section of the Milky Way galaxy is a mosaic of images from NASA’s Wide-field Infrared Survey Explorer, or WISE. The constellations Cassiopeia and Cepheus are featured in this 1,000-square degree expanse. These constellations, named after an ancient Queen and King of Ethiopia in Greek mythology, are visible in the northern sky every night of the year as seen from most of the United States.
To the unaided human eye, Cassiopeia is easily recognizable by the five bright stars that make up its “W” shape. However, WISE observed infrared light, where the sky takes on a very different appearance. The bright stars of the constellations fade into obscurity amongst the backdrop of millions of other stars revealed by WISE. Cool clouds of dust that fill the space between the stars in the Milky Way glow in infrared light and tell us more about the story of how stars are born, and how they die.
Within this image are dozens of dense clouds, called nebulae. Many of the nebulae seen here are places where new stars are forming, creating bubble like structures that can be dozens to hundreds of light-years in size. The process of star formation within these giant clouds has been likened to fireworks, celebrating the birth of new generations of stars. But the death of stars is also seen in the remnants of a supernova explosion that was witnessed by the astronomer Tycho Brahe in 1572 AD. This remnant is located about one-fifth of the way from left of center, and about one-sixth of the way up from the middle of the image.
The colors used in this image represent specific wavelengths of infrared light. Blue and cyan (blue-green) represent light emitted at wavelengths of 3.4 and 4.6 microns, which is predominantly from stars. Green and red represent light from 12 and 22 microns, respectively, which is mostly emitted by dust. This image is a mosaic of thousands of individual frames from WISE, combined first into 442 interlocking tiles before re-projecting and stitching them into the final picture. This was done for each of the four WISE wavelengths, totaling nearly 30 billion pixels in the interlocking tiles. Image credit: NASA/JPL-Caltech/UCLA
