ROYAL ASTRONOMICAL SOCIETY PRESS INFORMATION NOTE
16th April 2009
EMBARGOED UNTIL 0001 BST, 22ND APRIL 2009
Ref.: RAS PN 09/32 (NAM 19)

Issued by:

Dr Robert Massey
Press and Policy Officer
Royal Astronomical Society
Burlington House
Piccadilly
London W1J 0BQ
Tel: +44 (0)20 7734 3307 / 4582
Mob: +44 (0)794 124 8035
E-mail: rm@ras.org.uk

and

Anita Heward
Press Officer
Royal Astronomical Society
Mob: +44 (0)7756 034 243
E-mail: anitaheward@btopenworld.com

RAS website: http://www.ras.org.uk

EWASS meeting press room (20th – 23rd April only)
Tel:
+44 (0)1707 285530
+44 (0)1707 285640
+44 (0)1707 285781
+44 (0)1707 285587

EWASS home page: http://www.jenam2009.eu (map of campus at http://www.star.herts.ac.uk/ewass)

EWASS press page: http://www.star.herts.ac.uk/ewass/press

RAS PN 09/32 (NAM 19, EMBARGOED): X-RAY ASTRONOMERS FIND ‘GARDEN HOSE’ JET TRAIL NEBULA

Using the NASA Rossi X-ray Timing Explorer (RXTE) satellite, a team of astronomers have discovered an object predicted, but never seen before – a ‘jet trail’ nebula. Team leader Dr Klaas Wiersema of the University of Leicester will present the discovery on Wednesday 22nd April at the European Week of Astronomy and Space Science conference at the University of Hertfordshire.

The RXTE satellite has been scanning the centre of our galaxy every few days for the last years, searching for variable X-ray sources. Through these scans it has found a multitude of varying X-ray sources, most of which are thought to be X-ray binaries. These systems consist of a compact star (a neutron star or black hole) that pulls material away from a "normal" companion star. This material forms hot disks, which emit X-rays. X-ray binaries are also known to spout jets of gas at velocities very close to the speed of light.

While most of them are highly variable in intensity, there is also a subclass found by RXTE which is nearly constant in brightness and rather faint. It is this class of sources that Dr Wiersema and his team set out to study. They obtained accurate positions of the X-ray sources using the NASA Chandra X-ray space telescope and used the European Southern Observatory’s 3.6-m telescope at La Silla in Chile to search for the corresponding optical signals. The sources were then confirmed as X-ray binaries.

But one of these sources surprised the team. In addition to a faint optical source a bright large nebula (cloud of gas and dust) was visible on the optical images. This nebula consists of two stripes, and is like no other nebula seen before – it is a completely new class of object.

Careful measurements of the shape of the nebula helped the team to understand the origin of the nebula: it appears to be made by the powerful jets of the X-ray binary. The jets of the binary slam into the interstellar medium (ISM - the tenuous gas between the stars), where they make the gas radiate. As the binary moves rapidly through the galaxy, the jet-ISM interaction points move with it, creating the so-called "jet trails" we see in the image.

These trails had been predicted by theorists in the past, but despite searches were not seen before in other sources, as they require a rare set of circumstances to form: the X-ray binary has to move very rapidly (in this case about 100 km per second across the line of sight), and the interstellar medium has to be denser than normal.

Dr Wiersema compares the nebula pattern to garden hoses on soil. “Imagine holding two powerful hoses, pointing to the ground. Where the water hits the ground, mud splashes up. If you stand still, a large circular patch of mud would form and slowly spread out. But if you walk quickly across the garden, you make two parallel stripes of mud. The jets from the X-ray binary make the nebula in the same way.”

The accidental discovery of this nebula gives astronomers a powerful new tool to help them understand how X-ray binaries live their life. The power of the jet now and in the past can be derived from the shape and brightness of the nebula and shapes a new view of the way X-ray binaries produce these jets.

CONTACT

Dr Klaas Wiersema
Department of Physics and Astronomy
University of Leicester
University Road
Leicester LE1 7RH
United Kingdom
Tel: +44 (0)116 252 2377
Mob: +44 (0)77867 46313
E-mail: kw113@star.le.ac.uk

IMAGE

Images in different formats can be obtained from
http://www.star.le.ac.uk/~kw113/nam

The fan-like nebulosity is clearly visible in this image from the ESO 3.6-m telescope. The powerful jets emitted by the X-ray binary (which itself is too faint to see in this image) crash into the interstellar medium. Because this X-ray binary is moving quickly through space, it has a fast proper motion and drags these "impact points" along with it. This leaves two long "trails" behind: the two stripes of emission seen running diagonally across the image. Credit: K. Wiersema / ESO / University of Leicester

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.