An X-Ray Santa Claus in Orion (Forwarded)

ESA News
http://www.esa.int

30 November 2007

An X-Ray Santa Claus in Orion

Right in time for the festive season, ESA's XMM-Newton X-ray observatory has
discovered a huge cloud of high-temperature gas resting in a spectacular
nearby star-forming region, shaped somewhat like the silhouette of Santa
Claus.

An early present for astronomers, the cloud suggests that hot gas from many
star-forming regions leaks into the interstellar medium.

The Orion nebula is the nearest dense star-forming region to Earth that
contains stars much more massive than the Sun. XMM-Newton's newly-discovered
gas cloud is composed of winds blowing from these high-mass stars that are
heated to millions of degrees as they slam into the surrounding gas.

"There is one star in particular that dominates the nebula," says Manuel
Gudel, Paul Scherrer Institut, Switzerland, who led the team that discovered
the gas. The star in question is theta1 Orionis C, a giant star around 40
times mass of the Sun, with a surface temperature of 40,000 C. Gudel and his
colleagues think that the violent collision between the wind from this star
and the surrounding dense gas is largely responsible for the
newly-discovered hot gas cloud.

The high-temperature gas fills a region of the nebula that appears to be a
huge cavity in optical and infrared images. The new observations, taken with
XMM-Newton's European Photon Imaging Camera (EPIC) camera, suggest that
astronomers are seeing only a particular portion of the gas. The X-rays from
this portion escape absorption by patches of cold gas covering much of the
front of the Orion nebula.

The surrounding pattern of absorbing clouds gives the detected gas its Santa
Claus shape, with his prominent hat outlined by the northern gas bubble. In
its entirety, the hot gas probably fills the whole nebula.

The team discovered it whilst conducting a survey of the young stars in the
region. In the background of many of those images was a faint glow of
X-rays. "The diffuse signal came up time and time again. Finally, we
realized that it was something real," says Gudel.

The presence of the hot gas in a fairly common nebula like Orion is
surprising. Although theory has predicted such hot gas clouds, previous
observations suggested that a large number of massive stars shedding winds,
or supernova explosions are required. These are found in some regions of
vigorous high-mass star formation, which are scattered only rarely
throughout the galaxy. The new observations show that much smaller
collections of high mass stars can produce hot gas as well.

There are many star-forming regions similar to the Orion nebula throughout
the galaxy, so there should be a network of channels and bubbles being
filled up by the hot gas leaking from these various regions. "This is
another possible way to enrich the interstellar medium. You don't have to
wait for a sudden supernova to explode. You can do it with just one or two
massive stars over millions of years," says Gudel.

The team now plans to obtain new observations to determine how the gas flows
out of the Orion nebula. In particular, they want to see whether it connects
with a giant bubble created by supernova explosions from previous
generations of massive stars.

Notes for editors:

The paper reporting the discovery of the Orion plasma cloud, entitled "A
million-degree plasma pervading the extended Orion nebula" appears in
Science Express, the online version of the journal Science on 29 November
2007.

The paper was written by M. Gudel, K. Briggs T. Montmerle, M. Audard, L.
Rebull and S. Skinner.

For more information:

Manuel Gudel, Paul Scherrer Institut, Switzerland
Email: Guedel @ astro.phys.ethz.ch

Norbert Schartel, ESA XMM-Newton Project Scientist
Email: Norbert.Schartel @ esa.int

[NOTE: Images supporting this release are available at
http://www.esa.int/esaCP/SEMOCI73R8F_index_1.html ]