ROYAL ASTRONOMICAL SOCIETY PRESS INFORMATION NOTE
16th April 2009
EMBARGOED UNTIL 0001 BST, 22nd APRIL 2009
Ref.: RAS PN 09/31 (NAM 18)
Dr Robert Massey
Press and Policy Officer
Royal Astronomical Society
Mob: +44 (0)794 124 8035
Royal Astronomical Society
Mob: +44 (0)7756 034 243
RAS website: http://www.ras.org.uk
EWASS meeting press room (20th – 23rd April only)
+44 (0)1707 285530, +44 (0)1707
+44 (0)1707 285781, +44 (0)1707 285587
EWASS home page: http://www.jenam2009.eu
EWASS press page: http://www.star.herts.ac.uk/ewass/press
RAS PN 09/31 (NAM 18, EMBARGOED):
A PEANUT-SHAPED STELLAR EXPLOSION
Using the NASA / ESA Hubble Space Telescope (HST), an international team of astronomers have taken the first optical images of a dramatic stellar outburst and discovered a peanut-shaped bubble expanding rapidly into space. Team member Valerio Ribeiro, a graduate student from Liverpool John Moores University will present their results on Wednesday 22nd April at the European Week of Astronomy and Space Science conference at the University of Hertfordshire.
The scientists looked at a star in the constellation of Ophiuchus (known as RS Oph) which has undergone a series of outbursts over the last century. On 12th February 2006, Japanese amateur astronomers reported it had brightened once again and had even become visible to the unaided eye. This was the first eruption of RS Oph since 1985 and gave scientists the unprecedented opportunity to study it using new more powerful telescopes on the ground and in space, including the HST.
RS Oph consists of a white dwarf, a dead star about the size of Earth in orbit around a much larger star, a so called red giant. Due to its proximity the white dwarf pulls hydrogen rich gas from the outer layers of the red giant and roughly every 20 years the build up of gas on the white dwarf’s surface causes a cataclysmic thermonuclear explosion. The rise to maximum brightness takes place in less than a day and at its height the energy output of RS Oph increases to over 100,000 times that of the Sun. The eruption ejects a quantity of material equivalent to the mass of the Earth at speeds of several thousand kilometres per second.
The red giant is also continuously losing enormous amounts of gas in a wind that envelops the whole system. As a result, the explosion on the white dwarf occurs effectively inside its companion's atmosphere and the ejected gas then slams into it at very high speed.
Using the HST, observations of RS Oph were made 155 and 449 days after the outburst. Combined with spectroscopy from ground-based telescopes, the first images revealed a double-lobed “peanut” structure with material expanding outwards at between 1000 and 3000 km per second.
The team attribute the shaping of the nebula to the pre-existing red giant wind. In a binary system like this, material gathers towards the plane of the stars’ orbits while at the poles it is less dense. When the outburst takes place, the ejected material hits the high density gas in the orbital plane and slows down rapidly, while at the poles it moves more quickly. The result is the peanut shape seen in the HST images and confirmed earlier observations made using radio telescopes on the ground.
Valerio Ribeiro now hopes to watch RS Oph over the years to come. He comments, “There are some astronomers who believe systems like this will ultimately explode as supernovae. Our continuing work will help us find out if that will happen.”
Astrophysics Research Institute
Liverpool John Moores University
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Wirral CH41 1LD
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Mob: +44 (0) 7719810174
Media & PR Officer
University of Hertfordshire
Tel: +44 (0)1707 28 4095
Available from http://www.astro.ljmu.ac.uk/~var/images/images.html
Figure 1. An artist's impression of the binary star system RS Ophiuchi: hydrogen-rich gas transferred from a red giant onto the surface of a white dwarf has just exploded. (Credit: David A. Hardy http://www.astroart.org & Science and Technology Facilities Council)
Figure 2. An HST ACS image of RS Oph 155 days after outburst, clearly showing a double-lobed structure with one lobe apparently bigger than the other. North is up and east to the left. At a distance of around 5000 light years, the structure about 600 times the distance from the Earth to the Sun across and expanding at around 3000 km per second. Credit: NASA/HST and Valerio Ribeiro
NOTES FOR EDITORS
THE EUROPEAN WEEK OF ASTRONOMY AND SPACE SCIENCE
More than 1000 astronomers and space scientists will gather at the University of Hertfordshire for the European Week of Astronomy and Space Science (EWASS), incorporating the 2009 Royal Astronomical Society National Astronomy Meeting (RAS NAM 2009) and the European Astronomical Society Joint Meeting (JENAM 2009). The meeting runs from 20th to 23rd April 2009.
EWASS is held in conjunction with the UK Solar Physics (UKSP) and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST) meetings. The conference includes scientific sessions organised by the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) and the European Space Agency (ESA).
EWASS is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and the University of Hertfordshire, Hatfield.
THE ROYAL ASTRONOMICAL SOCIETY
The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.