A glitzy new family portrait of a star-forming region supports a theory that the universe's most massive stars carve out these wispy wombs and thereby enable stellar embryos to take shape.
The infrared photograph, which will be detailed in the Dec. 1 issue of The Astrophysical Journal, bolsters a long-held theory of star formation.
Stars are born within clouds of gas and dust that dot most galaxies. Scientists think that turbulence from the wind of other stars within these clouds gives rise to knots of material with enough mass that the gas and dust begins to collapse under their own weight. As the cloud collapses, the material heats up and forms an embryonic star, or "protostar," at its center. The protostar develops into a full-fledged star powered by thermonuclear fusion of hydrogen and other light elements in its core.
One theory describes a process whereby massive stars, weighing from 15 to about 60 times the mass of the sun, can trigger the formation of such clumps of material and, in turn, stellar newborns.
The theory goes these stars are so hefty 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.
As the winds and radiation make more elbow room, gas and dust get pushed against the rim of the cavity. Astronomers have long suspected that this compression ignites successive generations of stars along a cavity's expanding rim.
This result came into sparkling view with new images by NASA's Spitzer Space Telescope of a star-forming region called W5, which appears to span an area of the sky equal to four full moons and is located about 6,500 light-years away in the constellation Cassiopeia. A light-year is the distance light will travel in a year, or about 6 trillion miles (10 trillion kilometers).
The image showed a family of stars that got progressively younger with distance from a cavity center. So the elderly, most massive stars sat in the centers of W5's two hollow cavities and the younger stars lined the cavities' rims and tips of the region's elephant-trunk-like pillars.
This ladder-like separation of ages provides some of the best evidence yet, the researchers say, that massive stars give rise to younger generations.
"Triggered star formation continues to be very hard to prove," said lead researcher 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 team plans to follow up the study with more detailed measurements of the stars' ages to see if there is a distinct age difference between the stars just inside and outside the cavity rim.
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