29 November 2007

Million-degree galactic gas ‘bubbles’ found

Cosmos Online
Astronomers have found million-degree gas 'bubbles' in the Orion Nebula, revealing that stars in the stellar nurseries of our galaxy commonly generate waves of hot gas.
Million-degree galactic gas 'bubbles' found

Hot rays: A million-degree plasma cloud in the Orion Nebula. The blue indicates X-ray emissions from a hot plasma cloud in the Orion Nebula, detected by the XMM-Newton space observatory. The background image was recorded by NASA's Spitzer Space Telescope in the infrared, showing emissions from cool dust. Credit: Science

SYDNEY: Astronomers have found million-degree gas ‘bubbles’ in the Orion Nebula, revealing that stars in the stellar nurseries of our galaxy commonly generate waves of hot gas.

Orion is the closest star-forming region to Earth, and astronomers believe that our Sun was born in a similar environment. Stars in such nebula were thought to form in dense, very cold, molecular clouds. Now, however, a study published in U.S. journal Science reports that bubbles of superheated gas are also common, showering the nebula with X-rays.

“Every new piece of information we collect on Orion has implications for the early history of the Solar System, and therefore for our understanding of our own origins,” said lead author Manuel Guedel, an astronomer from the Paul Scherrer Institute in Switzerland.

Star Nurseries

Stars are born in these dense molecular clouds, in a process often triggered by shock waves from supernovae or the collision of two galaxies.

Initially, gravity pulls particles across vast distances in space towards a focal point in the cloud that will become the star’s centre. This process of contraction produces heat and – in combination with forces of gravity – nuclear fusion eventually begins, signifying the birth of a star.

The vast Orion constellation hosts a huge molecular cloud and the majority of this region is dark. The Orion Nebula itself is a bright area on the surface of this cloud facing Earth. In this region, a few hot stars – the so-called Trapezium stars – illuminate, ionise and excite the particles in the interstellar medium causing the emission of a characteristic reddish light.

Wind causes “gas bubbles”

The observations described in the new study were collected using the European Space Agency’s XMM-Newton, an orbiting X-ray observatory. X-ray-detecting telescopes have targeted the Orion Nebula for 30 years but Guedel and his team identified a “bright” patch that had gone unnoticed.

“We think that the winds from the Trapezium stars collide with the surrounding gas, and this creates shock waves that can indeed heat up to millions of degrees,” suggests Guedel.

Super-heated “gas bubbles” in star-forming regions were previously thought to be associated only with congregations of many massive stars. The observation of these hot spots in the Orion Nebula was a surprise given the small number of stars present.

The discovery has led the research team to propose that hot gas “bubbles” are much more common in the galaxy than astronomers previously thought.

The study also revealed that the hot gas does not rest inside the nebula but rather, flows out into the interstellar medium. “We suggest that large parts of the galaxy are enriched by such hot gas flows leaking out of many star-forming regions,” says Guedel.

“[These results] go some way towards giving us a picture of the Galaxy as an eco-system, with cycles of death and renewal,” comments Peter Tuthill, an astrophysicist from the University of Sydney in Australia, who was not involved in the study. “This is a small piece of a very big cosmic jigsaw.”


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