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 Nanostructures taste the rainbow
29.06.2017 | California Institute of Technology

nachricht X-ray photoelectron spectroscopy under real ambient pressure conditions
28.06.2017 | National Institutes of Natural Sciences

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: Making Waves

Computer scientists use wave packet theory to develop realistic, detailed water wave simulations in real time. Their results will be presented at this year’s SIGGRAPH conference.

Think about the last time you were at a lake, river, or the ocean. Remember the ripples of the water, the waves crashing against the rocks, the wake following...

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Nanostructures taste the rainbow

29.06.2017 | Physics and Astronomy

New technique unveils 'matrix' inside tissues and tumors

29.06.2017 | Life Sciences

Cystic fibrosis alters the structure of mucus in airways

29.06.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>