Binary Pulsars Prove General Relativity

Most of space is relatively flat, so large, well confined masses are required to bend space to any significant degree in order to test Einstein’s theory. Without exceptional preparation, this means either a neutron star or a black hole is required. A pulsar, a type of neutron star that emits radio waves in regular pulses because of its rapid rotation, may be preferred, however. The chief advantage of a pulsar over a non-pulsing neutron star (or black hole) is that any distortion that occurs to the regular radio pulses can be used to measure the gravitational effects causing the distortion. For example, the rare binary pulsar system, PSR J0737-3039A/B, offers a unique window into the effect of General Relativity as it is a system where each star is only 20 km across, with a million kilometer separation between the two, and an orbital period of 2.4 hours.

PhysicsWeb is reporting that Michael Kramer and colleagues at Jodrell Bank Observatory have verified Einstein’s theory of General Relativity by observing PSR J0737-3039A/B. The team measured four effects, three of which are the rates at which "the pulsars are slowing down and spiraling in towards each other as they lose energy by emitting gravitational waves" and "pulses from one star are being slowed by the other star’s gravitational pull and by the curved space-time around them," in addition to the mass ratio of the two stars. They then plugged this information into Einstein’s equations and compared the results to their observations giving an accuracy of 99.5%. Next, "Kramer … wants to improve the precision of his measurements still further," noting that at some point General Relativity must fail "as it does not describe nature on small scales."