It's a star-eat-star world out there. Even peaceful-looking parts of the Milky Way can harbor stars of such ferocious heat and radiation that their smaller, cooler kin dare not pass too closely lest their surrounding disks of gas and dust--and with them the capacity to form planets--get blown away. Astronomers have now made the first map of these stellar danger zones in an effort to narrow the range of possible star systems that contain planets capable of supporting life.
Sitting atop the stellar pecking order are stars tagged with the letter O, the biggest, hottest, and most active of the lot. O-stars shine with blue light and can burn as much as 10 times hotter than G-stars such as our sun; they're also up to 100 times more massive and more than a million times brighter. During an O-star's relatively short lifetime of a few million years--before it explodes as a supernova--its rapid rotations generate intense solar winds and deadly radiation, both wreaking havoc in the vicinity. In the denser parts of the Milky Way, where stars are particularly close together, O-stars can strip away the planet-building potential of many of their neighbors in a process called photoevaporation.
Astronomers using NASA's Spitzer Space Telescope have mapped a stellar group being picked clean of its planetary disks by O-stars. In the 20 May Astrophysical Journal, a team led by Zoltan Balog of the Steward Observatory at the University of Arizona in Tucson reports surveying 1000 stars in the Rosette Nebula, located about 5200 light-years away in the constellation Monoceros. As "one of the nearest and most spectacular high-mass star-forming regions," Balog says, the area is ideal for testing the effects of photoevaporation. The researchers found that among stars located more than 16 trillion kilometers away from O-stars--or about 1.7 light-years--around 45% retained their planetary disks. But as stars ventured closer to the big Os, that percentage dropped precipitously. The 16-trillion-kilometer perimeter seems to be "sharply defined," says Balog.
The findings provide more evidence that star and planet formation is "turning out to be even more complex than we expected," says astrophysicist James Lloyd of Cornell University. Just like the material that supernovae eject into space, Lloyd says, the disks blown away by the actions of O-stars will eventually cool and collapse to form a new generation of stars and planets.