More GR confirmation - A Massive Pulsar in a Compact Relativistic Binary

[imatfaal]

 

There are strong arguments for GR not to be valid beyond a (yet unknown) critical point, like its incompatibility with quantum theory and its prediction of the formation of spacetime singularities under generic conditions. Therefore, it remains an open question if GR is the final description of macroscopic gravity. This strongly motivates testing gravity regimes that have not been tested before, in particular regimes where gravity is strong and highly non-linear...

 

...The consistency of the observed GW damping (Pb ) with the GR predictions for PSR J0348+0432 (Table 1) implies |αPSR − α0 | < 0.005 (95% confidence) and consequently excludes significant strong-field deviations, even for massive NSs of ∼ 2 [solar masses].

 

 

 

 

published article http://www.sciencemag.org/content/340/6131/1233232

 

pre-print http://arxiv.org/abs/1304.6875

 

podcast including discussion

http://www.sciencemag.org/content/340/6131/499.2.full

Pulsar Tests Gravity

 

Because of their extremely high densities, massive neutron stars can be used to test gravity. Based on spectroscopy of its white dwarf companion, Antoniadis et al. (p. 448) identified a millisecond pulsar as a neutron star twice as heavy as the Sun. The observed binary's orbital decay is consistent with that predicted by general relativity, ruling out previously untested strong-field phenomena predicted by alternative theories. The binary system has a peculiar combination of properties and poses a challenge to our understanding of stellar evolution.

Not sure yet how this differs from previous observation of decay of orbit fitting with general relativity's prediction of energy being radiated through gravitational wave - but will update if/when I realise what the new bit is.

 

http://phys.org/news/2013-04-einstein-gravity-theory-toughest-bizarre.html

[Royston]

Not sure yet how this differs from previous observation of decay of orbit fitting with general relativity's prediction of energy being radiated through gravitational wave - but will update if/when I realise what the new bit is.

 

 

It states the distinction in the abstract...

 

'However, the most massive NSs known today reside in long-period binaries or other systems unsuitable for GW (gravitational wave) radiation tests. Identifying a massive NS in a compact, relativistic binary is thus of key importance for understanding gravity-matter coupling under extreme conditions'

From the discussion...

'The orbital period of PSR J0348+0432 is only 15 seconds longer than that of the double pulsar system, but it has 2 times more fractional gravitational binding energy than each of the double pulsar NSs. This places it far outside the presently tested binding energy range [see Fig. 4a & (8)].Because the magnitude of strong-field effects generally depends non-linearly on the binding energy, the measurement of orbital decay transforms the system into a gravitational laboratory for a previously untested regime, qualitatively very different from what was accessible in the past.'

It goes on to explain that if GR becomes invalid at these extreme conditions, there would be a violation of the strong equivalence principle i.e the gravitational field is independent of an objects position and velocity. Such a violation would lead to GW emission deviating from the predictions of GR. I assume this rules out Brans-Dicke theory, not sure on the details though.

EDIT: On further reading it doesn't rule out Brans-Dicke theory.

Edited April 26, 2013 by Royston

[imatfaal]

Thanks Royston - I hadn't appreciated that to me a slight change was actual a step change.