Discovery of the 1000th Pulsar
13 November 1998
An international team of researchers using a giant radio telescope in Australia, equipped with a new "multibeam" receiver system, has just discovered the 1000th pulsar to be found within our Galaxy since the first few were discovered in Cambridge in 1967.
The team of researchers, comprised of astronomers from the UK, Australia, Italy and the USA, have been surveying the plane of 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 Nuffield Radio Astronomy Laboratories, Jodrell Bank, 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 being made with the 76-metre Lovell Radio Telescope at Jodrell Bank.
Thanks to this new, state-of-the-art system, the survey is discovering new pulsars at a rate more than 10 times greater than any previous search has achieved - about one for every hour of observing time. It has already added more than 200 new pulsars to the nearly 800 known when the survey began about a year ago. By the end of the survey, in around a year or so's time, it is expected that over 600 additional pulsars will have been discovered.
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 be 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 team are hoping that they might soon discover a neutron star in orbit around a black hole. Dr Dick Manchester, leader of the Australian group, explains that "theories predict that around one in a thousand pulsars may be orbiting a black hole. If such a pair were to be found, it would give us the ability to learn far more about black holes, which are such elusive and enigmatic objects."
Supporting Material and Quotations by team members:
The survey is proving so successful partly because, as Professor Lyne explains, "the observations are at an unusually high frequency - around 15 times that used for FM radio transmissions - where pulsar signals pass relatively unhindered through interstellar space." He adds that "the natural hiss of the Milky Way, our Galaxy, which is a nuisance for pulsar hunters, is also reduced at these frequencies, so easing the search."
Nevertheless, even surveys like this can only find a fraction of the 300,000 pulsars thought to exist in our galaxy. "Many have signals that are too weak to pick up, or their beams are not pointing towards us" points out Dr Dick Manchester, the leader of the Australian group within the pulsar team. "Like people, pulsars are all individual and have their own characteristic signals. We want to get beyond this and understand how they actually emit their signals."
The team members at the Massachusetts Institute of Technology have developed methods of eliminating sources of radio interference, such as satellite signals, from the data which can masquerade as "fake" pulsars. As Professor Victoria M. Kaspi, points out, "Interference from human sources is a growing problem in radio astronomy and we are having to strive ever harder to observe through it."
Pulsars are also called "neutron stars" as their interior is composed of neutrons covered by a crust of iron and nickel. Dr Nichi D'Amico, team member from Bologna, Italy, points out that "the centre of a pulsar is denser than an atomic nucleus - a lump the size of a sugar cube would weigh 100 million tons!"
"Signals from distant pulsars can be also used to probe the conditions in the depths of our Galaxy" explains Dr Fernando Camilo of the University of Manchester. "The space between the stars contains giant, invisible clouds of electrons threaded with magnetic fields, which blur the pulsar signals that travel through them. By unravelling this blurring, the conditions in space can be reconstructed. The survey has, so far, doubled the number of really distant pulsars known so enabling us to probe the galaxy out to more than 20,000 light years."
Pulsars could even help increase our understanding of the evolution of the Universe. As Professor Kaspi explains, "observations of rapidly rotating pulsars spread across the galaxy may enable us to detect a background of gravitational waves. The pulsar signals are affected as a gravity wave passes by them in much the same way a buoy in the sea responds to a passing wave. Precise measurements can then shed light on how the Universe has evolved from the Big Bang era to the Universe that we see today."
The research team members are:
Dr Nichi D'Amico, Observatorio Astronomico di Bologna.
Professor Victoria Kaspi and Mr Froney Crawford, Massachusetts Institute of Technology .
For Futher Information Contact:
Background information about Pulsars may be found in: Jodrell Bank Pulsar Research Web site: http://www.jb.man.ac.uk/~pulsar/