Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

General relativity survives gruelling pulsar test

18.09.2006
Astronomers have used a pair of pulsars orbiting each other, found with CSIRO’s Parkes telescope in 2003, to show that Einstein’s theory of general relativity is correct to within 0.05% – the most stringent limit to date.
They also hope to be able to use the two pulsars to determine the exact nature of the matter that pulsars and other neutron stars are made of.

Their results are to be published in the journal Science, and made available online in Science Express Science Express [external link] on 14 September 2006.

An international research team led by Professor Michael Kramer of the University of Manchester's Jodrell Bank Observatory, UK, has been observing the double-pulsar system since 2003 with three of the world’s largest radio telescopes: CSIRO’s Parkes radio telescope in NSW, Australia; the Lovell Telescope near Manchester, UK; and the Robert C. Byrd Green Bank Telescope in West Virginia, USA.

The double-pulsar system, whose pulsars are called PSR J0737-3039A and B, is the only known system of radio pulsars orbiting each other. It lies 2000 light-years away in the direction of the constellation Puppis.

The system consists of two massive, highly compact neutron stars, each weighing more than our own Sun but only about 20 km across, orbiting each other every 2.4 hours at speeds of a million kilometres per hour.

Separated by a distance of just a million kilometres, both neutron stars emit lighthouse-like beams of radio waves that are seen as radio ’pulses‘ every time the beams sweep past Earth.

By precisely measuring the variations in pulse arrival times, the researchers found the movement of the stars to exactly follow Einstein's predictions. "This is the most stringent test ever made of GR in the presence of very strong gravitational fields—only black holes show stronger gravitational effects, but they are obviously much more difficult to observe,” Professor Kramer says.

Co-author Ingrid Stairs, an assistant professor at the University of British Columbia in Vancouver, Canada, says it is possible to measure the pulsars’ distances from their common centre of mass. "The heavier pulsar is closer to the centre of mass, or pivot point, than the lighter one and this allows us to calculate the ratio of the two masses,” she says.

This mass ratio is independent of the theory of gravity, and so tightens the constraints on general relativity and any alternative gravitational theories.

Other relativistic effects predicted by Einstein can be observed: the fabric of space-time around pulsar B is curved, and the other pulsar’s “clock” runs slower when it is deeper in the gravitational field of its massive companion. Each of these effects provides an independent test of general relativity.

The distance between the pulsars is shrinking by 7 mm a day. Einstein's theory predicts that the double pulsar system should be emitting gravitational waves – ripples in space-time that spread out across the Universe at the speed of light.

"These waves have yet to be directly detected,” says team member Prof. Dick Manchester of CSIRO’s Australia Telescope National Facility ATNF). "But, as a result, the double pulsar system should lose energy causing the two neutron stars to spiral in towards each other by precisely the amount that we have observed – thus our observations give an indirect proof of the existence of gravitational waves."

The astronomers hope that over the next few years they can make even more precise measurements of the characteristics of the system, allowing them to measure the moment of inertia of a neutron star. (“Moment of inertia” is a measure of how much a body resists a force trying to rotate it.) “This measurement may be very difficult but if we could do it to just a precision of 30 per cent, we could distinguish between the many different ideas about the nature of the matter that makes up neutron stars,” says team member Dr George Hobbs of the ATNF.

Technical note

Six parameters are measured in the tests of general relativity. They relate to:

- the relativistic precession of the orbit
- variations in the Doppler effect and gravitational redshift as the pulsar moves around its elliptical orbit
- the time variation in the orbital period
- the Shapiro delay, which describes a delay to a pulse travelling through the - curved space-time of a massive object, and
- the mass ratio derived from the measured semi-major axes of the orbits.

Helen Sim | EurekAlert!
Further information:
http://www.csiro.au

More articles from Physics and Astronomy:

nachricht Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology

nachricht NASA team finds noxious ice cloud on saturn's moon titan
19.10.2017 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Physics boosts artificial intelligence methods

19.10.2017 | Physics and Astronomy

NASA team finds noxious ice cloud on saturn's moon titan

19.10.2017 | Physics and Astronomy

New procedure enables cultivation of human brain sections in the petri dish

19.10.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>