An international team of scientists from the UK, Australia, Italy and the USA have announced in today's issue of the journal Science Express (8th January 2004) the first discovery of a double pulsar system.
They have shown that the compact object orbiting the 23-millisecond pulsar PSR J0737-3039A with a period of just 2.4 hours is not only, as suspected, another neutron star but is also a detectable pulsar, PSR J0737-3039B, that is rotating once every 2.8 seconds.
Professor Andrew Lyne of the University of Manchester points out that "While experiments on one pulsar in such an extreme system as this are exciting enough, the discovery of two pulsars orbiting one another opens up new precision tests of general relativity and the probing of pulsar magnetospheres."
The same team previously reported [Nature 4th December 2003], the discovery of pulsar A in a close binary system which is rapidly losing energy by gravitational radiation. The stars will coalesce in only approximately 85 million years, sending a ripple of gravity waves across the Universe. The discovery of the system shows that such coalescences will occur more frequently than previously thought. "The news has been welcomed by gravitational wave hunters, since it boosts their hopes for detecting the gravitational waves" says Prof. Nichi D'Amico of Cagliari University.
The double neutron star system was first detected using the 64-m Parkes radio telescope in New South Wales, Australia. Subsequent observations were made both at Parkes and with the 76-m Lovell Telescope of the University of Manchester in Cheshire, UK and revealed the occasional presence of pulsations with a period of 2.8 seconds from the companion pulsar.
Already, four different effects beyond those explained with simple Newtonian gravity have been measured and are completely consistent with Albert Einstein's theory. Dr. Richard Manchester of the Australia Telescope National Facility says, "The fact that both objects are pulsars enables completely new high-precision tests of gravitational theories. This system is really extreme." Future observations of the two stars will measure their slow spiral in towards each other as they radiate gravitational radiation -- a dance of death leading to their ultimate fusion into what may become a black hole. General relativity predicts that the two stars will slowly wobble like spinning tops allowing new tests of the theory.
Another unique aspect of the new system is the strong interaction between radiation from the two stars. By chance, the orbit is seen nearly edge on to us, and the signal from one pulsar is eclipsed by the other. Dr. Andrea Possenti of Cagliari Astronomical Observatory says, "This provides us with a wonderful opportunity to probe the physical conditions of a pulsar's outer atmosphere, something we've never been able to do before."
The surveys designed by the team to discover new pulsars at the Parkes Telescope have been extraordinarily successful. They have discovered over 700 pulsars in the last 5 years, nearly as many as were discovered in the preceding 30 years. The discovery of this double pulsar system will be the major jewel in the crown.
A.G. Lyne, M. Burgay, M. Kramer, A. Possenti, R.N. Manchester, F. Camilo, M.A. McLaughlin, D.R. Lorimer, N. D'Amico, B.C. Joshi, J. Reynolds and P.C.C. Freire. "A Double-Pulsar System - A Rare Laboratory for Relativistic Gravity and Plasma Physics". Science 8 January 2004.
A pulsar is the collapsed core of a massive star that has ended its life in a supernova explosion. Weighing more than our Sun, yet only 20 kilometres across, these incredibly dense objects produce beams of radio waves which sweep round the sky like a lighthouse, often hundreds of times a second. Radio telescopes receive a regular train of pulses as the beam repeatedly crosses the Earth so the objects are observed as a pulsating radio signal.
Pulsars make exceptional clocks, which enable a number of unique astronomical experiments. Some very old pulsars, which have been "spun up" to speeds of over 600 rotations per second by material flowing onto them from a companion star, appear to be rotating so smoothly that they may even "keep time" more accurately than the best atomic clocks here on Earth. Very precise timing observations of systems in which a pulsar is in orbit around another neutron star have been able to prove the existence of gravitational radiation as predicted by Albert Einstein and have provided very sensitive tests of his theory of General Relativity -- the theory of gravitation which supplanted that of Isaac Newton. The neutron star binary system reported in this paper is one of these systems, with an orbit which is decaying more rapidly than any previously discovered.
The Parkes survey using a multi-beam system that led to the discovery of the double-pulsar system is an international collaboration of a team of astronomers from the UK, Australia, Italy and the USA. The researchers have been surveying our Galaxy, the Milky Way, for new radio pulsars using the 64-metre Parkes Radio Telescope in New South Wales, Australia. The powerful new "multibeam" receiver was built as a joint venture between engineers at the Australia Telescope National Facility and the University of Manchester's Jodrell Bank Observatory, funded by the Particle Physics and Astronomy Research Council.
The receiver gives the telescope 13 beams capable of scanning the sky simultaneously and, as Professor Andrew Lyne of the University of Manchester explained, "It's like having over a dozen giant radio telescopes operating at once". As a result, the system requires 13 sets of sophisticated data acquisition systems, one for each beam, which were largely developed and built by the UK group. Following initial detection at Parkes, confirmation and follow-up observations for many of the new pulsars are made with the 76-metre Lovell Radio Telescope at Jodrell Bank. The main processing of the survey in which the PSR J0737-3039 system was discovered was conducted on a cluster of computers at Cagliari Astronomical Observatory.
Images and Animations
More images and animations representing this system can be found at http://www.jb.man.ac.uk/research/pulsar/doublepulsar/
[Image and animation 1:
* Web Images (JPG, ~40KB) http://www.atnf.csiro.au/news/press/neutron_binary/images_3/anim2_0475.JPG
* Broadcast Images (TIFF, broadcast quality) ftp://ftp.atnf.csiro.au/pub/people/wri192/double_pulsar/PulsarsEvolutionTIFFS/
* Web (MPEG2 320x256, 5MB)
Formation of the double pulsar system. The first-formed pulsar is 'spun up' to become a rapidly rotating 'millisecond pulsar' by matter accreting from its red giant companion.
Evolution animation: How the double pulsar system formed. The double pulsar probably formed from a pair of massive stars orbiting each other. (This animation does not show the orbital motion.) The more massive star ended its life first, swelling to become a red giant and then exploding as a supernova, its core forming a pulsar. The second star entered the red giant phase later: when it did, matter from this star was transferred onto its pulsar companion, spinning that up to become a fast-rotating "millisecond" pulsar. The red giant then went supernova, forming the second, slower, pulsar.
Animation: John Rowe Animation
[Image and animation 2:
* Web Images (JPG, ~40KB) http://www.atnf.csiro.au/news/press/double_pulsar/images/
* Broadcast Images (TIFF, broadcast quality) ftp://ftp.atnf.csiro.au/pub/people/wri192/double_pulsar/PulsarsCurrentTIFFS/
* Web (MPEG2 320x256, 3MB) http://www.atnf.csiro.au/news/press/double_pulsar/mpegs/PulsarsCurrent320x256.mpg
* PAL (MPEG2, 20MB)
* NTSC (MPEG2, 17MB)
Current state of the double pulsar system.
Animation: John Rowe Animation