SEATTLE - Scrappy little newborn stars appear to be forming in one of the most violent regions known in space. Despite radiation levels that cook the fledglings, threatening to blow them to smithereens, researchers are surprised by how they resiliently cling to cocoons of dust that might form planets.
The potential stars are hidden inside the dust left behind in their creation. These enveloping protoplanetary dust disks, or proplyds, as they are called, are in a massive struggle against mighty radiation foes.
The outcome bears on how easy it is for planets to form in the universe, because most stars are cooked up in intense star-formation regions like those involved in the new work. Astronomers believe that our own solar system may have formed in one of these chaotic areas, only to be booted out to its present, more placid location in space.
A pair of findings announced here today at a meeting of the American Astronomical Society leave astronomers wondering what's going on.
Here's what was found:
Dozens of massive stars in the Carina Nebula fry protoplanetary disks around presumed newborn stars with massive doses of ultraviolet radiation. The UV rays cook the dust by a process called photoevaporation.
Based on what astronomers knew about disk destruction in another chaotic part of space, they did not expect to find any of these tadpole-like proplyds in Carina, due to its overwhelming UV power.
The other new observations, of the Orion Nebula, confirm that a massive star there can blow a dust disk away in about 100,000 years.
"We're literally watching these disks evaporate before our eyes as the overwhelming energy of the nearby hot stars bears down on them," said Mark Morris, a UCLA researcher involved in the Orion study.
Orion is dominated by one star that causes most of the destruction. The Carina Nebula, on the other hand, contains 60 "incredible monsters," said study leader Nathan Smith of the University of Colorado. Each is more massive than the biggest star in Orion, and the overall radiation is 100 times stronger in Carina.
Smith and his colleagues took a close-up look at Carina with the National Science Foundation's Blanco telescope in Chile. They found the first large population of protoplanetary disks ever seen outside Orion. They were surprised to find any.
"These things should be getting cooked faster," Smith said of Carina's proplyds. Yet instead Carina's disks are huge. Each one is about 100 times the diameter of our solar system. Orion's dust disks are mostly just a bit larger than our solar system.
"This suggests that planetary disks may be more resilient or more common than previously thought," Smith said.
Resilient or fleeting?
The apparent contradiction in the two findings may have a simple answer. Star formation and protoplanetary disk development may simply happen differently in different regions of space, said UCLA's Ralph Shuping, who led the Orion study, which was based on new images obtained with the Keck Observatory in Hawaii.
Both groups agree that further work is needed to resolve the differences.
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