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Orion Nebula X-rays Worth a Second Look



Composite image of XMM-Newton data and Spitzer observations showing the Orion Nebula (upper left) and the newly-discovered gas bubble (in blue).

In science, double checking is essential. This is a lesson astrophysicist Thierry Montmerle from LAOG 1 and his colleagues have taken to heart. They found a previously undetected cosmic phenomenon, a huge gas bubble in the Orion Nebula, using the European Space Agency’s XMM-Newton satellite, which observes X-ray energies in the cosmos.
Orion isn’t obvious ground for astronomical breakthroughs–it was first observed in 1610 and has been intensely studied since. Moreover, Montmerle explains that NASA’s Chandra satellite, which has a superior resolution to XMM-Newton, had recently done a deep scan of the same area. The XMM observations were already a few years old when Montmerle and colleagues from Europe and the U.S. pulled the data. “No one had looked at it, because we didn’t expect much, in view of the Chandra results,” explains Montmerle. XMM-Newton boasts a wider field of view than Chandra, and has greater sensitivity to low X-ray energies. Montmerle and his colleagues were surprised, on looking at the old data, to discover an enormous plasma bubble, heated to a temperature of roughly 1 million degrees that earlier observations had missed. 2
Their hypothesis is that the X-ray emitting plasma, which is too cool to come from any of the nearby stars, is the result of tumult within the nebula. The Orion nebula is a nursery of sorts–a turbulent region where a cluster of massive young stars was born about 3 million years ago. Montmerle explains that these young stars shed an enormous amount of mass in their stellar infancy, at a velocity of 1,500 km per second. This violent stellar wind interacts with the nebula, creating powerful shocks. These shocks, in turn, create the pervasive X-rays unveiled by XMM-Newton.
As Montmerle is keen to point out, “it is widely believed that our own Sun, and the proto-planetary disk that eventually coalesced 4.5 billion years ago into today’s solar system, was formed in conditions similar to those in Orion.” If so, the discovery of this X-ray plasma bubble may shed light on the early stages of the Earth’s formation.
“We would like to examine the interaction of this wind and the proto-planetary disk,” says Montmerle. “Many others are interested in this work–a good thing considering the massive task at hand.”

Mark Reynolds

Notes :

1. Laboratoire d'Astrophysique de Grenoble (CNRS / Université Joseph Fournier).
2. Manuel Gűdel et al., “Million degree plasma pervading the extended Orion nebula.” Science, 2008. 319: 309-12.

Contacts :

Thierry Montmerle,
LAOG, Grenoble.


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