Strange Binary Star System Reveals Einstein's Theory of Gravity Holds True

We may have some new answers when it comes to Einstein's gravity theory. A strange stellar pair, which includes a massive neutron star in orbit with a companion white dwarf star, has allowed researchers to put two competing theories of gravity to the test.

The two stars are nearly 7,000 light years from Earth, orbiting each other once every two and a half hours. The pair includes a newly-discovered pulsar, which is a spinning neutron star with twice the mass of the sun, and a white dwarf, which is a very dense, dying star. Discovered with the National Science Foundation's Green Bank Telescope (GBT), the stars were studied by astronomers in both visible light and with radio observations.

In this type of star system, the orbits decay over time and gravitational waves are emitted. These waves carry energy from the system itself. By very precisely measuring the time of arrival of the pulsar's radio pulses over a long period of time, astronomers were able to determine the rate of decay and the amount of gravitational radiation emitted.

In fact, the system lent itself perfectly for testing alternative theories of gravity; astronomers couldn't have hoped for a better example. The main factors that make this particular system such a good one to study are the closeness of the neutron star's orbit with its companion and the fact that the companion white dwarf is compact but not another neutron star.

So what exactly was at stake? Under the extreme conditions of this system, some scientists believed that the equations of General Relativity might not accurately predict the amount of gravitational radiation being emitted. This, in turn would change the rate of orbital decay. There are competing gravitational theories to Einstein's that some believed would prove more accurate in this case.

"We thought this system might be extreme enough to show a breakdown in General Relativity," said Paulo Freire, one of the researchers, in a news release. "But instead, Einstein's predictions held up quite well."

The researchers plan to use instruments in order to detect and study the gravitational waves emitted as dense pairs such as neutron stars and black holes spiral inward toward collisions. They expect that they will probably need to know the characteristics of the waves that they seek, but this new finding could put them on the right path for doing so. The results have confirmed that the filtering techniques planned for these instruments remain valid.

The findings are published in the journal Science.