An extraordinary binary star system (two stars orbiting around each other) 3,000 light years away has been discovered and studied by scientists, as it provides a unique test of Einstein's theory of gravity. Scientists refer to this as the theory of general relativity, which overthrew Newton's theory of gravity when Einstein published it in 1915. One of the consequences of Einstein's theory is the existence of a phenomenon called 'gravitational radiation'. The theory says that this is produced when massive objects, such as stars, move rapidly relative to each other. But what is gravitational radiation? It is worth noting that it is unlike any other radiation with which we are familiar (such as light, or radio waves). The theory predicts that massive objects warp, or distort, the very fabric of space and time, and in certain circumstances the distortion can propagate like a wave, producing gravitational radiation. This is something that we have yet to observe directly, as the technology required to do this is extremely challenging. However, we can confirm its existence indirectly by observing unusual distant objects, such as the binary system mentioned above.
The particular binary system, entitled rather unimaginatively J0651, consists of two 'white dwarf' stars orbiting at a distance from each other of about 1/3 the Earth-moon distance (approximately 125,000 km). They are both quite massive objects, one star being 25% the mass of the Sun and the other about 55% . But the amazing thing is that they complete an orbit around each other in only 12 minutes and 45 seconds. A simple sum tells us that they are traveling at about 520 km/sec - not bad! However, the evidence supporting the emission of gravitational radiation comes from looking at how the orbit period (time for the stars to go round each other) is changing. The emission of the radiation causes the system to lose energy, resulting in the change in orbit period. In the 13 months since the object was discovered the orbit period has changed by less than 1/1000 th of a second, but over time this change will lead to the two stars coming together in about 900,000 years time. The study of this extreme object provides another test for Einstein's theory, which it passes very neatly, within the tolerances of the current observations. See http://arxiv.org/abs/1107.2389/ for the abstract of the paper.
The reason I found this particularly interesting is that I did my PhD thesis way back in the dark ages (1975) on the 'cosmological implications of gravitational radiation' ... and we are still finding difficulty directly observing this particular prediction of Einstein's theory of gravity. This will have to await the launch of very sophisticated gravitational wave detectors into space.
The particular binary system, entitled rather unimaginatively J0651, consists of two 'white dwarf' stars orbiting at a distance from each other of about 1/3 the Earth-moon distance (approximately 125,000 km). They are both quite massive objects, one star being 25% the mass of the Sun and the other about 55% . But the amazing thing is that they complete an orbit around each other in only 12 minutes and 45 seconds. A simple sum tells us that they are traveling at about 520 km/sec - not bad! However, the evidence supporting the emission of gravitational radiation comes from looking at how the orbit period (time for the stars to go round each other) is changing. The emission of the radiation causes the system to lose energy, resulting in the change in orbit period. In the 13 months since the object was discovered the orbit period has changed by less than 1/1000 th of a second, but over time this change will lead to the two stars coming together in about 900,000 years time. The study of this extreme object provides another test for Einstein's theory, which it passes very neatly, within the tolerances of the current observations. See http://arxiv.org/abs/1107.2389/ for the abstract of the paper.
The reason I found this particularly interesting is that I did my PhD thesis way back in the dark ages (1975) on the 'cosmological implications of gravitational radiation' ... and we are still finding difficulty directly observing this particular prediction of Einstein's theory of gravity. This will have to await the launch of very sophisticated gravitational wave detectors into space.
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