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RAS PN06/18 (NAM11): Bubble, bubble: searching through the rubble of supernova remnants

Last Updated on Sunday, 01 December 2013 20:40
Published on Wednesday, 05 April 2006 00:00
Rosat_thumb.jpgA 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 5th 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

Rosat_thumb.jpgCaption: ROSAT All Sky Survey ©  Snowden S. L. et al., “First Maps of the Soft X-ray Background from the Rosat XRT/PSPC All-Sky Survey,” 1995, ApJ, 454, 643-653






 


Interstellar_structures_thumb.jpg
Caption: Cartoon showing a vertical slice through the Galactic Plane, showing the various interstellar structures and the lines of sight of the observed fields. © Michelle Supper




LHB_boundary_thumb.jpg
Caption: All-sky absorption map showing distance to the Local Hot Bubble boundary. © Dr Richard Willingale

 





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/area/index.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
Mob: +44 (0)7881824419
This email address is being protected from spambots. You need JavaScript enabled to view it.
From 4th – 7th April, Mrs Supper can also be contacted through the NAM press office. Tel: (0116) 2297474 or (0116) 2297475

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
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.