One of the most fantastic predictions of Einstein’s general theory of relativity has been the existence of gravitational radiation.
Should gravitational waves be real, it means that the empty space as a medium for propagation of gravitational waves can itself oscillate and move. Since its prediction in 1917, a lot of research has been made to discover gravitational waves. Although there has been indirect evidence for gravitational radiation, yet there has been no direct proof of their existence. In comparison with normal mechanical vibrations, the gravitational wave can be described as vibration and deformations of space. Since the strength of the gravitational wave is by far much weaker than electromagnetic waves by a rough coefficient of 10-38 (the coupling coefficient of the gravitational field is 10 -40) they are much harder to detect.
Experimental evidence for gravitational radiation
The main question about gravitational radiation is how these waves are produced. In contrast to electromagnetic waves that can be easily produced by simple technology and tools like radio transmitters, due to their small strength, no detectable gravitational wave can be produced by a human being. Indeed, in order to produce them, extremely gigantic devices are required that are beyond the present level of human technology.
One strong source of gravitational waves is the center or each galaxy, where there is a high level of the annihilation of matter or inhalation of the nearby matter by the existing huge black holes that reside at the center of the galaxy. The other source is binary neutron stars or black holes. The idea is quite simple. Since, like any other type of radiation, gravitational waves carry energy; therefore, in a binary system, part of the energy is emitted as gravitational radiation due to the rotational motion of the constituent stars with a frequency twice that of the orbital frequency. This in turn leads to the binary’s gradual change of orbit and getting close to each other. This effect can indeed be measured. For ordinary planets and even stars, the effect is very small. For example, the amount of gravitation radiation of the Jupiter-Sun system is of the order of 400W!! However, for binaries composed of neutron stars or black holes the effect is considerable and can be detected.
Until know the most indirect evidence of gravitational radiation had come from the famous experiment of astrophysicist John Taylor (physics Nobel Prize winner in 1993). Through careful observation of a binary of pulsars (small but extremely dense pulsating stars), he managed to show that the estimated value of the speed decrease of the binary stars coincided with the measured quantity with a very high level of precision, proving that the emission of gravitational radiation was the only factor.
But a recent report by a team of Columbia University astronomers may make research on this topic much easier. In a recent report, on Sept. 24, 2015, edition of Science Daily, astronomer Zoltan Haiman explained the discovery of two black holes in Virgo constellation that are heading for a huge collision. According to him, the two orbiting black holes are in quasar PG 1302-102- about 3.5 billion light-years away- about 1-2 light weeks apart. They are expected to collide within one million years. The power of this collision is estimated to be that of 100 million supernovas!
According to researchers at the California Institute of Pasadena, such a collision will have the power sufficient for destroying a whole galaxy. Although the timing of the collision is too long in our normal lifetime scale, thanks to the knowledge that they have gained in this discovery, astrophysicists hope to find similar black hole binaries in the next decade. In that case, they will have the best chance to investigate the mysteries of gravitational radiation and find a direct proof for that.
“The detection of gravitational waves lets us probe the secrets of gravity and test Einstein’s theory in the most extreme environment in our universe — black holes,” said Daniel D’Orazio from the Columbia University.
Almost a century after the introduction of Einstein’s general theory of gravitation, the next decade may be a turning point for our knowledge about gravity.
- Black holes and Gravitational Waves
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