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Gravitational Waves Angelina Dirina Astronomy 101 Spring 2016 Gravitational Waves • Waves that travel at the speed of light and transmit distortions of space through the universe. • These are caused by sudden changes of curvature of spacetime, and move outward through the universe like ripples in a pond. • While highly plausible through Einstein’s theories of relativity, no waves were proven or detected until very recently. Theories of Relativity • Gravitational waves were predicted by Einstein’s theories of relativity. • Special relativity (1905) states that space and time are intertwined, but does not address gravity. • General relativity (1915) presents gravity into interactions between space and time. Based on this theory, gravity can distort and change interactions of space and time. Spacetime & Curvature • In order to understand gravitational waves, we must remember that spacetime deals with four dimensions of possible motion: length, width, depth, and time. • Within these four dimensions, gravity allows for the curvature of spacetime. • According to Einstein, objects with large gravitational force create that curvature, such as the Earth going around the Sun – this proves that spacetime is curved around the Sun. Ways to Manipulate Curvature • Greater curvature of spacetime = stronger gravity • 1 way: increase the mass of an object, and you will have greater gravitational attraction, hence more curvature in spacetime • Another way: increase the density of an object’s mass by making it smaller, like a star that becomes compressed into a black hole. • Black holes have very strong gravitational attraction, so strong that nothing that comes near them can escape. Source: APA Discovery! • In September 2015, the gravitational-wave detector detected a small ripple in spacetime • This ripple was caused by the merging of two black holes colliding a billion light years away • Their gravitational energy combined was so powerful that this ripple traveled through the universe, and eventually made it through Earth Source: LIGO Discovery! • Finally, Einstein’s theories on gravitational energy were proven true, indicating that gravity can produce curvatures in spacetime that expand and travel great distances • These waves traveled at the the speed of light and compressed spacetime as they traveled, which is how LIGO was able to detect them Source: Forbes New Ways to Look at the Universe • The waves detected by LIGO in September are only one kind of gravitational energy people can learn about in the future • With these new understandings, we can develop a better knowledge of how the universe works New Ways to Look at the Universe • With these discoveries, we can now observe and study: – Compact, fast-moving objects: like the wave already detected by LIGO – Slower, or more massive objects: all sorts of objects emit gravity in space, but many of them do not have very strong gravitational energy, so their signals are harder to detect. A larger interferometer, like one that could be in space, would potentially be able to detect these New Ways to Look at the Universe With these discoveries, we can now study and observe: – Ultra-massive black hole orbits and mergers: quasars at the centers of galaxies had to get that big somehow, and often their low frequency gravitational emissions have been impossible to detect – Relic gravitational wave emissions from the Big Bang: such emissions have also been hard to detect, but they exist at all frequencies and can offer us a better understanding of the universe. Frequencies Source: Minglei Tong Connection to Other Waves? • On the same day as LIGO’s discovery, Fermi, a gamma way detector, detected a burst of gamma rays 0.4 seconds after the gravitational wave discovery • Scientists are beginning to think that the events might be connected, though that would be a puzzling reality Connected to Other Waves? • Short gamma wave bursts allow scientists to see hidden cosmic events, typically the mergers of neutron stars, or neutron stars and black holes • The idea of gamma waves being produced from two black holes is controversial – the merger of black holes is not supposed to generate light Gamma Wave Emissions Dying star producing gamma waves. Gamma Waves • Gamma waves produce the most energetic type of light in the electromagnetic spectrum • They are supposed to have very little to do with black hole mergers: black holes are expected to merge “cleanly,” and without producing any light Connected to Other Waves? • If gravitational waves and gamma ray bursts are linked, scientists will have to explain what could cause bursts of light in correspondence with black hole mergers. The discovery of gravitational waves combined with an understanding of gamma wave bursts opens new questions about physics and the universe. • This is a question that has not been considered before, and further demonstrates how more observations of gravitational waves can help us understand the universe better