Bubble, bubble: searching through the rubble of supernova remnants(Forwarded)

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Bubble, bubble: searching through the rubble of supernova remnants

A study of supernova remnants -- material blown out into space
during death throes of giant stars -- has shown that a bubble
of gas enveloping our Solar System is being shoved backwards
by the debris of another, more recent, supernova.

Over the last few million years, several stars have exploded
within the Milky Way and they have left behind bubbles of
expanding, hot gas that radiate low-energy X-rays. The Solar
System sits within one of these shells, known as the "Local
Hot Bubble". A study using data from the XMM-Newton Space
Telescope has shown that the "Loop 1 Superbubble", the remnants
of some more recent supernova explosions, is expanding faster
than the Local Hot Bubble and is compressing an area of cool
dense gas, known as the Wall, that lies between the two shells.
Although astronomers have known for some time that the Local
Hot Bubble has an hourglass shape, pressure and density
measurements from this new study provide evidence that Loop 1's
compression of the Wall is causing the hourglass's "waist".

"The X-ray radiation from the bubbles is very faint. In order
to see them, we've had to remove all the light from stars,
nebulae and cosmic rays the images, leaving only the weak
X-ray signal. It's the astronomical equivalent of looking at
an aquarium, ignoring the fish and looking only at the water,"
said Michelle Supper, who is presenting the results at the
RAS National Astronomy Meeting in Leicester on 5 April.

"We've taken long-exposure images of ten small areas of sky in
the direction of the Loop 1 Superbubble, then removed all the
bright objects and studied what's left. Each structure emits
a unique x-ray signal, like a fingerprint, that reflects its
temperature and chemical composition. This means that, when we
come to analyse the images, we can tell which bits of radiation
originated from Loop 1, the Wall or the Local Hot Bubble,"
Supper explained.

Together with Dr Richard Willingale, also from the University
of Leicester, Supper developed mathematical models to represent
each of the structures and then produced a geometrical model
from which she could work out the distances to the structure
boundaries and the pressure and density of the interstellar
plasma within the structures.

Loop 1 is thought to be expanding because it is being inflated
by winds originating from a group of stars known as the Scorpius-
Centaurus Association. Supper's measurements of physical
properties of the Wall showed that its density increases
fourfold, reaching a peak near the most indented region of the
Local Hot Bubble. The pressures also peak around this point,
indicating that the Wall is pushing into the bubble at in
this region. The chemical analysis showed that the highest
concentrations of gases are found at the centre of the Loop 1
Superbubble and levels decrease dramatically in the expanding
shell of the bubble.

"Not many astronomers are looking at these structures at present
but this study has shown there are many more mysteries to solve!"
adds Supper. "We found that X-ray emissions in an area near the
galactic plane are much higher in energy than expected but we
don't know yet whether we've discovered a new X-ray source or
whether its an extension of the very high energy radiation coming
from the centre of the galaxy. We hope that this study will also
give us an insight into the distribution of the Galactic Halo, a
mysterious X-ray signal that can be detected faintly above and
below the disc of the Milky Way.

IMAGES

Images can be found at:
http://www.ras.org.uk/index.php?opti...sk=view&id=970

FURTHER INFORMATION

The Local Hot Bubble

The Local Hot Bubble is a cool, old supernova remnant that
envelopes the solar system and much more besides. It is not
spherical, more like the shape of a bent hourglass or a peanut
shell. The edge of the bubble is at least 91 light years away in
the Northern fields, rising to 358 light years in the Southern
fields.

Loop 1 superbubble

The Loop 1 Superbubble is a big, young, hot supernova remnant that
is located approximately 684 light years away from the Sun and is
about 895 light years in diameter.

XMM-Newton Space Telescope

XMM-Newton was launched in December 1999 and is operated by the
European Space Agency. It is the biggest scientific satellite ever
built in Europe.

For more information see:
http://sci.esa.int/science-e/www/are...cfm?fareaid=23

CONTACTS

Mrs Michelle Supper
X-ray and Observational Astronomy Group
Department of Physics & Astronomy
University of Leicester
Leicester, LE1 7RH
UNITED KINGDOM
Tel: +44 (0)116 252 3497

From 4 - 7 April, Mrs Supper can also be contacted through the
NAM press office (see details at the top of the release)

Dr R Willingale
X-ray and Observational Astronomy Group
Department of Physics & Astronomy
University of Leicester
Leicester, LE1 7RH
UNITED KINGDOM
Tel: +44 116 252 3556