CAC - Noticias

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'Gravitational waves will teach us about the dark side of the Universe, things that don't shine' Posted: 13 Feb 2014 01:59 AM PST What is a gravitational wave? In Einstein’s general theory of relativity from 1915, changes in gravity travel as waves. If you think of space and time as making up a flexible membrane then gravitational waves are ripples in the surface. Alternatively, this about how the surface of a pond changes when you throw in a stone; waves move out from the centre. An exploding star leads to gravitational waves moving away from the source in a similar fashion, although they move at the same speed as light. How do they come about? Gravitational waves are generated whenever there are changes on the gravitational field, say when two stars orbit around one another. There are tiny levels of gravitational waves from the Moon circling around the Earth, and even tinier ones from ice skaters doing pirouettes. In order for them to be strong enough that there is any chance of detection you need to turn to the most violent phenomena in the Universe; exploding stars, colliding stars, the birth of black holes and the origin of the Universe itself. Have any been discovered? Only indirectly from systems with two neutrons stars, which radio observers see as pulsars. The orbit of such systems have been observed to change at the rate predicted by Einstein’s theory. Why are they so hard to physically detect? The may come from the most powerful events in the Universe, but they come to us from large distances and they get weaker as they spread out from the source. When they reach our detectors they stretch and squeeze the instruments an amount that requires a resolution better than the size of the atomic nucleus. This is an awesome challenge for engineering and it is truly impressive that we have instruments actually operating at this level. What kind of information can they bring to the scientific community? They will teach us about the dark side of the Universe, things that don’t shine. Black holes, neutron stars and the mess associates with supernova explosions are all of interest to the gravitational-wave astronomer. Why are they key to our understanding of the universe? Together with quantum theory, General Relativity is a fundament for modern physics. Gravitational waves represent the one prediction of Einstein’s theory that have so far not been tested directly. Unlocking this mystery will allow us to probe the kind of physics that is too extreme for our laboratories (even the Large Hadron collider!) What tools are scientists developing to be able to physically measure their existence? Experimenters are using a vastly upscaled version of the classic Michelson-Morley interferometer, bouncing intense laser light off of mirrors at the end of two perpendicular arms. By measuring the difference in travel time in the two arms one can deduce if a gravitational wave has passed through the instrument. It is a very difficult experiment. What is going to develop in this area in the near future? The detectors are currently being improved to include new technology. They will start taking data again in the next two years, and the expectation is that they will then be able to “see” much further out into the Universe than previously. What do scientists expect to happen in the coming years? If our understanding of astrophysical systems is largely correct then the next generation of detectors should observed many binary black hole and neutron star systems in a year of observation. This would be a revolution crowning many decades of technology developments. But it would only be the beginning. Future, even more sensitive instruments, are already on the drawing board for the next decade. This includes flying a gravitational-wave detector in space to observe waves from collision of the massive black holes that live at the centre of galaxies.

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