Pulsar find boosts hope for gravity-wave hunters (Forwarded)

Australia Telescope National Facility
Commonwealth Scientific and Industrial Research Organisation
Epping, Australia

Contacts:

Italy
Ms Marta Burgay
University of Bologna, Department of Astronomy
+39-051-209-5719
Email:

Professor Nicolò D'Amico
Director, Cagliari Astronomical Observatory
Tel: +39-070-711-80-208
Cell: +39-329-660-38-28
Email:

UK
Professor Andrew Lyne
University of Manchester, Jodrell Bank Observatory
+44-(0)-1477-572640
Email:

Australia
Dr Dick Manchester
CSIRO Australia Telescope National Facility
+61-2-9372-4313
Email:

USA
Assistant Professor Vicky Kalogera
Northwestern University
+1-(847)-491-5669
Email:

Embargoed to 0500 December 4 Australian Eastern Summer Time (1800 December 3 GMT
/ 1300 December 3 Eastern US time) in accordance with publication in Nature,
December 4.

Pulsar find boosts hope for gravity-wave hunters

Neutron star pairs may merge and give off a burst of gravity waves about six
times more often than previously thought, scientists report in today's issue of
the journal Nature [4 December]. If so, the current generation of gravity-wave
detectors might be able to register such an event every year or two, rather than
about once a decade -- the most optimistic prediction until now.

Gravity waves were predicted by Einstein's general theory of relativity.
Astronomers have indirect evidence of their existence but have not yet detected
them directly.

The revised estimate of the neutron-star merger rate springs from the discovery
of a double neutron-star system, a pulsar called PSR J0737-3039 and its
neutron-star companion, by a team of scientists from Italy, Australia, the UK
and the USA using the 64-m CSIRO Parkes radio telescope in eastern Australia.

Neutron stars are city-sized balls of a highly dense, unusual form of matter. A
pulsar is a special type -- a spinning neutron star that emits radio waves.

PSR J0737-3039 and its companion are just the sixth known system of two neutron
stars. They lie 1600-2000 light-years (500-600 pc) away in our Galaxy.

Separated by 800,000 km -- about twice the distance between the Earth and Moon
-- the two stars orbit each other in just over two hours.

Systems with such extreme speeds have to be modelled with Einstein's general
theory of relativity.

"That theory predicts that the system is losing energy in the form of gravity
waves," said lead author Marta Burgay, a PhD student at the University of Bologna.

"The two stars are in a 'dance of death', slowly spiralling together."

In 85 million years the doomed stars will fuse, rippling spacetime with a burst
of gravity waves.

"If the burst happened in our time, it could be picked up by one of the current
generation of gravitational wave detectors, such as LIGO-I, VIRGO or GEO," said
team leader Professor Nicolò D'Amico, Director of the Cagliari Astronomical
Observatory in Sardinia.

The previous estimate of the neutron-star merger rate was strongly influenced by
the characteristics of just one system, the pulsar B1913+16 and its companion.
PSR B1913+16 was the first relativistic binary system discovered and studied,
and the first used to show the existence of gravitational radiation.

PSR J0737-3039 and its companion are an even more extreme system, and now form
the best laboratory for testing Einstein's prediction of orbital shrinking.

The new pulsar also boosts the merger rate, for two reasons.

It won't live as long as PSR B1913+16, the astronomers say. And pulsars like it
are probably more common than ones like PSR B1913+16.

"These two effects push the merger rate up by a factor of six or seven," said
team member Dr Dick Manchester of CSIRO.

But the actual numerical value of that rate depends on assumptions about how
pulsars are distributed in our Galaxy.

"Under the most favourable distribution model, we can say at the 95% confidence
level that this first generation of gravitational wave detectors could register
a neutron star merger every one to two years," said Dr Vicky Kalogera, Assistant
Professor of Physics and Astronomy at Northwestern University in Illinois, USA.

Dr Kalogera and colleagues Chunglee Kim and Duncan Lorimer have modelled binary
coalescence rates using a range of assumptions.

The new result is "good news for gravity-wave astronomers," according to team
member Professor Andrew Lyne, Director of the Jodrell Bank Observatory of the
University of Manchester in the UK.

"They may get to study one of these cosmic catastrophes every few years, instead
of having to wait half a career," he said.

Publication

M. Burgay, N. D'Amico, A. Possenti, R.N. Manchester, A.G. Lyne, B.C. Joshi, M.A.
McLaughlin, M. Kramer, J.M. Sarkissian, F. Camilo, V. Kalogera, C.Kim & D.R.
Lorimer. "An increased estimate of the merger rate of double neutron stars from
observations of a highly relativistic system". Nature 426, 531-533 (2003).

Images and Animations

[Animation 1]
Pulsar J0737-3039 and its neutron-star companion. The system is emitting gravity
waves, shown here as ripples in a spacetime grid. Animation: John Rowe Animation

* Web Image (JPG, 110KB)
http://www.atnf.csiro.au/news/press/...anim1_0272.JPG
* Broadcast Images (TIFF, broadcast quality)
http://www.atnf.csiro.au/news/press/...nary/images_1/
* Web (MPEG2 320x256, 3MB)
http://www.atnf.csiro.au/news/press/...nim320x256.mpg
* PAL (MPEG2, 20MB)
http://www.atnf.csiro.au/news/press/...rstAnimPAL.mpg
* NTSC (MPEG2,16MB)
http://www.atnf.csiro.au/news/press/...stAnimNTSC.mpg

[Animation 2]
The pulsar and its companion merging. The merged object may become a black hole.
Animation: John Rowe Animation

* Web Image (JPG, 89KB)
http://www.atnf.csiro.au/news/press/...anim2_0475.JPG
* Broadcast Images (TIFF, broadcast quality)
http://www.atnf.csiro.au/news/press/...nary/images_2/
* Web (MPEG2 320x256, 5MB)

http://www.atnf.csiro.au/news/press/...nim320x256.mpg
* PAL (MPEG2, 29MB)
http://www.atnf.csiro.au/news/press/...ondAnimPAL.mpg
* NTSC (MPEG2, 24MB)
http://www.atnf.csiro.au/news/press/...ndAnimNTSC.mpg

[Image 1:
http://www.atnf.csiro.au/news/press/...kes_medres.jpg (65KB)]
The Parkes Radio Telecope. Photo: CSIRO