Where is the gas in interstellar space? (Forwarded)

Royal Astronomical Society
London, U.K.

Issued by RAS Press Officers:

Robert Massey
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AND
Anita Heward
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CONTACT:

Professor Martin Barstow
University of Leicester
Tel: +44 (0)116 252 3492

On 17 and 19 April, Professor Barstow can be contacted via the NAM press
office (see above).

PRESS INFORMATION NOTE: RAS PN 07/17 (NAM 13)

EMBARGOED FOR 00:01 BST, TUESDAY 17 APRIL 2007

WHERE IS THE GAS IN INTERSTELLAR SPACE?

A team of astronomers led by Professor Martin Barstow of the University of
Leicester have searched for the hot gas thought to be present in the
interstellar space around the Sun but found it just isn't there.

Speaking at the Royal Astronomical Society National Astronomy Meeting in
Preston on Tuesday 17 April, Professor Barstow will present a map of the
local interstellar medium, the gas lying between the stars out to
distances of about 300 light years from the Sun, made using the Far
Ultraviolet Spectroscopic Explorer (FUSE) satellite.

Professor Barstow and his team used FUSE to observe a group of white dwarf
stars (compact remnants of stars like our Sun will be at the end of its
life). The scientists intended to probe the structure of interstellar
space in the vicinity of the Sun by searching for the imprint of oxygen in
the ultraviolet light from the stars. However, all the oxygen detected was
found to be in the atmospheres of the stars and no interstellar oxygen was
found. This implies that, rather than being full of tenuous ionized gas,
as expected, this region of interstellar space (the Local Cavity) is
actually empty and was probably swept clear by an ancient supernova
explosion a few million years ago.

Our present picture of the local interstellar medium is that the Sun and
Solar system are embedded in and near the edge of a wispy diffuse cloud,
known as the Local Cloud (or Local Fluff). This cloud, which is only 20-30
light years across, is itself in a larger much less dense region called
the Local Bubble or Local Cavity.

The gas in the Local Cavity was expected to bear the scars of recent
nearby events, such as supernova explosions, and radiation from hot young
stars. These would make the cavity gas hot and ionized, with the electrons
stripped from the constituent atoms, and should be detected by FUSE. The
hot gas should emit also X-rays that are detected as a diffuse background
in X-ray telescopes. However, if there is no hot gas present, then we need
to find another explanation for this X-ray background. One novel
suggestion is that it arises from the exchange of charged particles at the
boundary between the Sun's magnetic field and interstellar space.

NOTES FOR EDITORS

The 2007 RAS National Astronomy Meeting is hosted by the University of
Central Lancashire. It is sponsored by the Royal Astronomical Society and
the UK Science and Technology Facilities Council.

This year the NAM is being held together with the UK Solar Physics (UKSP)
and Magnetosphere, Ionosphere and Solar-Terrestrial (MIST) spring
meetings. 2007 is International Heliophysical Year.

The FUSE satellite was launched on 24 June 1999 and is a collaboration
between NASA and other space agencies.

IMAGES:

Images can be found at
http://www.nam2007.uclan.ac.uk/press...20070417h1.doc (2.3MB)
and
http://www.nam2007.uclan.ac.uk/press...20070417h2.doc (419KB)