Space.com | Science | 18 Aug 2010
Orion nebula making wavesYoung, massive stars have been caught setting off ripples through a giant space cloud in the same way that wind drives waves on the ocean.
The intermittent ripples were seen in a molecular cloud associated with the Orion nebula, a well-known stellar nursery within the constellation Orion.
A new study led by Olivier Berne of Leiden University in the Netherlands found that intense radiation emitted by nearby stars more massive than our sun was at the root of the process. The research is detailed in the Aug. 19 issue of the journal Nature.
Berne and his colleagues think the ripples are a signature of the high-velocity "wind" from the stars that once blew across the cloud surface.
"We think it happened less than 1 million years ago, which is somewhat recent in astronomical scales," Berne told SPACE.com.
Massive stars make their mark
The Orion cloud's young, massive stars emit radiation that interacts with the surrounding molecular gas and dust in their birth-cloud. Astronomers had thought this interaction could compress or fragment the cloud, but until now, there had been no clear evidence of such occurrences.
Berne and his colleagues observed the ripples at the surface of the Orion cloud and determined that the process is similar to a familiar one on Earth.
"In simple terms, it is the same type of ripples that you can see at the surface of the ocean when the wind is blowing over the water," Berne said. "So what we think is happening is that the massive stars that are nearby, they blow winds of ionized gas, and this wind is running over the interstellar clouds and making these ripples in a similar way."
When massive stars form, they produce very energetic ultraviolet light, Berne explained. This light heats the surrounding gas to temperatures of over 1,800 degrees Fahrenheit (1,000 degrees Celsius). Scientists call the cosmic ripple effect the Kelvin–Helmholtz instability.
- Nature 466 (19 Aug 2010) Editor's Summary
The molecular cloud in the Orion nebula, at about 414 parsecs from Earth, gives us our closest view of massive-star formation. It has been predicted from star-formation models that the gases heated and ionized in the process will generate wave-like structures as they are blown over pre-existing molecular gas. These waves have now been observed, in a new series of radio maps of the Orion nebula. The waves are thought to result from Kelvin–Helmholtz instability, a phenomenon seen at the interface between fluids with different densities and velocities, and further observations of such periodic structures should provide insight into the mechanisms of massive-star formation and its effects on the surrounding region of the molecular cloud.
- Nature 466 (19 Aug 2010) DOI: 10.1038/466928a
- Nature 466 (19 Aug 2010) DOI: 10.1038/nature09289