Einstein proven right again!
That's the world's most popular science headline. And from beyond the grave, the frizzy-haired physics sensation added another trophy to his mantle last week. A bit of astronomical audaciousness reconfirms Einstein's famous theory of gravity, General Relativity.
The gravitational test took place 1,700 light years away from Earth where a pair of super-heavy compressed stars rotate around each other. (See them here.) They're less than 800,000 miles apart, completing an orbit every two hours and 24 minutes. Both are neutron stars, the collapsed corpses of exploded stars whose gravity has scrunched the remains of a supernova down into a 14 mile-diameter composed solely of neutrons, the uncharged atomic particles found in the center of atoms. The collapse that produced the neutron stars literally squeezed the neutrons out of their original atoms. The only things in the universe denser than neutron stars are black holes.
Mere neutron stars are odd enough, you might suppose, but the gravity-testing stars, given the catchy names PSR JO737-3039 A and PSR JO737-3039 B, are even weirder. As described in the current edition of the journal Science, they are both pulsars, neutron stars that spin like tops — one rotates once every 23 milliseconds and the other every 2.8 seconds — and shoot out blasts of radio waves along their magnetic poles. Pulsars are the lighthouses of deep space; when first spotted in the 1967, some astronomers wondered if pulsars were signs of alien civilizations.
Now about 1,700 pulsars are known, but the only closely-rotating pulsar pair is the aforementioned PSR JO737-3039 A and B, first spotted in 2003. The two stars regularly eclipse each other, blocking their regular radio-wave blasts for about 30 seconds each time, their relatively close proximity to each other forcing pulsar B to wobble on its axis.
Decades before the discovery of neutron stars, Einstein predicted just this sort of wobble — and wobble is the word he used — would been seen in such stars as an effect of the strong gravity of two such massive objects pulling upon each other at close quarters. Decades before anyone even spotted a neutron star, Einstein's 1915 theory of General Relativity not only predicted such wobbles but estimated how much a pulsar would wobble, based on its size.
Because of the tight eclipses of these two pulsars, which scientists can observe with radio telescopes, measuring pulsar B's wobble with a high degree of accuracy was possible. In the study led by physicist Rene Breton of Canada's McGill University, Einstein's predictions were put to the test. A few alternative theories of gravity suggest that such stars would stand still or wobble in the opposite direction than the one predicted by General Relativity, Breton and colleagues note.
The researchers monitored the double pulsar from 2003 to 2007 with the National Science Foundation's Green Bank Telescope in West Virginia. For pulsars the size of the study pair, Einstein predicted wobble of pulsar B would be about 5 degrees every year. The team measured it as 4.77 degrees plus or minus 0.6 degrees, per year. Einstein triumphs again.