Einstein’s theory of general relativity is with us for more he 90 years and new discovery proved again that one of the greatest scientist was right.
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In the new issue of Science, one of the world's leading scientific journals, the work from the international scientific group confirms Einstein's work by observing a binary-pulsar star system. Researchers from McGill University’s Department of Physics lead the obervation of small and very dense stellar objects know as pulsars. When a massive star die and explode as supernovae, a pulsar is born.
It is very small, it can be compared with the area of a typical town, but it has a mass greater than that of our Sun. Pulsars spin at high speed, generate extremely strong gravity field and thus emit strong beams of radio waves from the northern and southern magnetic poles. Pulsars can be imagined as stellar lighthouse.
There are more than 1,700 pulsars in our galaxy and one of them, crypiticaly named PSR J0737-3039A/B, is the only double-pulsar system. To be more precise, it is the only double-pulsar system that human kind discovered. Double-pulsar means that two pulsars rotates around each other in close orbit. Since the pulsars are small and their orbit is small, the whole system is as large as our Sun.
Binary pulsars are the best place to test general relativity in a strong gravitational field. Einstein's theory predicted that, in such a field, an object's spin axis should slowly change direction as the pulsar orbits around its companion. Imagine a spinning top when its slightly non-vertical: the spin axis slowly changes direction, an elegant motion called 'precession.’"
The scientists discovered that one of the two pulsars is indeed precessing just as Einstein's 1915 theory predicts. If Albert Einstein had been wrong, the pulsar wouldn't be precessing, or would precess in some other way.
Pulsars are too small and too distant objects so we can't observe their orientation directly. However, the scientist realized that they could make measurements using the eclipses visible when one of the twin pulsars passes in front of the other.
When this occurs, the magnetosphere of the first pulsar partly absorbs the radio “light†being emitted from the other, which allows the researchers to determine its spatial orientation. After four years of observations, they determined that its spin axis precesses just as Einstein predicted.
Even though spin precession has been observed in Earth’s solar system, differences between general relativity and alternative theories of gravity might only shake out in extremely powerful gravity fields such as those near pulsars, Breton explains: “However, so far, Einstein’s theory has passed all the tests that have been conducted, including ours. We can say that if anyone wants to propose an alternative theory of gravity in the future, it must agree with the results that we have obtained here.â€
Breton, Kaspi and colleagues in Canada, the United Kingdom, the U.S., France and Italy studied the twin-pulsar using the 100-metre Robert C. Byrd Green Bank Radio Telescope at the National Radio Astronomy Observatory in Green Bank, WV.
“I think that if Einstein were alive today, he would have been absolutely delighted with these results,†said Dr. Michael Kramer, Associate Director of the Jodrell Bank Centre for Astrophysics at Manchester University. “Not only because it confirms his theory, but also because of the novel way the confirmation came about.†■
There are more than 1,700 pulsars in our galaxy and one of them, crypiticaly named PSR J0737-3039A/B, is the only double-pulsar system. To be more precise, it is the only double-pulsar system that human kind discovered. Double-pulsar means that two pulsars rotates around each other in close orbit. Since the pulsars are small and their orbit is small, the whole system is as large as our Sun. 
Pulsars are too small and too distant objects so we can't observe their orientation directly. However, the scientist realized that they could make measurements using the eclipses visible when one of the twin pulsars passes in front of the other.