Sounds

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Listen to a variety of sounds that scientists hope to hear with Gravitational Waves (Gravitational Wave: A gravitational disturbance that travels through space like a wave. This type of wave is analogous to an Electromagnetic Wave. Gravitational waves are given off by most movements of anything with mass. Usually, however, they are quite difficult to detect. Physicists are currently working hard to directly detect gravitational waves. Experiments like LIGO and LISA are designed for this purpose. ) (Thanks to Teviet Creighton for these sounds).

Neutron (Neutron: One of the particles in an atomic nucleus. These particles have no electric charge, but they hold together the protons (positive particles in a nucleus), and account for roughly half of the particles in the nucleus. Neutrons are fermions, and are believed to form the majority of the matter in a neutron star.) Stars (Neutron Star: A type of star which is very old, having cooled off and stopped nuclear fusion reactions. When gravity pulls the star down on itself, the electrons and protons are squeezed together, leaving just neutrons. The star is then supported against gravity by "neutron degeneracy pressure" (no two neutrons can be in the same place at the same time). These are produced when a star is too heavy to be a white dwarf (White Dwarf: A type of star which is very old, having cooled off and stopped nuclear fusion reactions. A white dwarf is supported by "electron degeneracy pressure" (no two electrons can be in the same place at the same time). These are produced when a star is not heavy enough to turn into a Neutron Star or a Black Hole. )})|white dwarves}), but not heavy enough to turn into a Black Hole. ) and Pulsars (Pulsar: A neutron star with a very high rate of spin (Spin: An intrinsic property of particles. (That is, a property which does not change. Mass and electric charge are examples of intrinsic properties.) Spin is related to the usual notion of spin, though it is a little more difficult to understand. Spin comes in units of 1/2, so that a particle may have a spin of 0, 1/2, 1, 3/2, and so on. A particle's spin determines whether it is a Fermion or a Boson.), and very intense magnetic fields. The pulsar gives off beams of radiation along its magnetic poles. If these poles are not aligned with the spin poles, the beam will sweep around like the beam of a lighthouse. )

Pulsars re rapidly-spinning stars. As they spin, any bumps on (or in) the stars will give off gravitational waves. Because these stars are so amazingly dense, and spin so amazingly quickly, the gravitational waves may be strong enough to detect on Earth. The sound produced will be a single, simple tone.

Black Holes (Black Hole: A region of spacetime (Spacetime: A concept in physics which merges our usual notion of space with our usual notion of time.) where the warpage of both space and time (gravity) is so intense that nothing — even light — can ever escape. Objects may fall in to the Black Hole, but once they pass the Event Horizon (Event Horizon: A surface — like the one surrounding a Black Hole — enclosing a region of space from which nothing (even light) can ever escape.), they can never escape again. Most Black Holes believed to exist are thought to be formed in the collapse of very large stars, or the collision of stars or other Black Holes. )})|blackholes})

According to General Relativity (General Theory of Relativity: Einstein's version of the laws of physics, when there is gravity. Building on the Special Theory of Relativity (Special Theory of Relativity: Einstein's version of the laws of physics, when there is no gravity. The two fundamental concepts in the foundation of this theory are equality of observers, and the constancy of the speed of light. The first of these means that the laws of physics must be the same, no matter how quickly an observer is moving. The second means that everyone measures the exact same speed of light. This theory is useful whenever the effects of gravity can be ignored, but objects are moving at nearly the speed of light. It has been successfully tested many times in particle accelerators, and orbiting spacecraft. For objects moving much more slowly than light, Special Relativity (Special Theory of Relativity: Einstein's version of the laws of physics, when there is no gravity. The two fundamental concepts in the foundation of this theory are equality of observers, and the constancy of the speed of light. The first of these means that the laws of physics must be the same, no matter how quickly an observer is moving. The second means that everyone measures the exact same speed of light. This theory is useful whenever the effects of gravity can be ignored, but objects are moving at nearly the speed of light. It has been successfully tested many times in particle accelerators, and orbiting spacecraft. For objects moving much more slowly than light, Special Relativity becomes very nearly the same as Newton's theory, which is much easier to use. ) becomes very nearly the same as Newton's theory, which is much easier to use. ), this theory generalizes Einstein's work so that the laws of physics must be the same for all observers (Observer: A person or piece of equipment that measures something in physics. Frequently, we speak of an observer measuring time or a distance in a particular place. ), even in gravity. Einstein showed that gravity is best understood as a warping of the geometry of spacetime, rather than as a pulling of objects on each other. The crucial idea is that objects move along geodesics — which are determined by the warping of spacetime — while spacetime is warped by massive objects according to the formula \(G = 8 π T\). ) theory — as it is currently understood — a black hole (Black Hole: A region of spacetime where the warpage of both space and time (gravity) is so intense that nothing — even light — can ever escape. Objects may fall in to the Black Hole, but once they pass the Event Horizon, they can never escape again. Most Black Holes believed to exist are thought to be formed in the collapse of very large stars, or the collision of stars or other Black Holes. ) must be a very simple object. It cannot have any bumps or ripples on its surface for very long. Of course, as something falls into the black hole, the hole must ripple. As the hole settles back down to its quiet, simple state, it will shake off gravitational waves.

Compact Binaries (Compact Binary: A specific type of Binary system in which both members are compact (meaning they are White Dwarfs, Neutron Stars, or Black Holes) and have roughly equal mass. )

A Compact Binary (Compact Binary: A specific type of Binary system in which both members are compact (meaning they are White Dwarfs, Neutron Stars, or Black Holes) and have roughly equal mass. ) is a pair of compact objects — white dwarfs, neutron stars, or black holes — in orbit around each other. As they orbit, they give off energy in the form of gravitational waves. This lost energy draws them closer, and causes their orbits to speed (Speed: For a wave, the speed of a particular point (such as its crest).) up, which makes the sound of their gravitational waves increase in pitch, until they finally meet and merge. The merger (Merger: The portion of the Inspiral of a binary system in which the individual objects are highly distorted, and their orbit is changing rapidly. This portion is not well-understood, and must be simulated using Numerical Relativity (Numerical Relativity: The branch of Relativity research which deals with simulating the development of Spacetime, using computers. This is believed to be the only possible way to understand things like the merger of two Black Holes.).) represents a mysterious part of General Relativity theory. Physicists expect to find some of the most interesting behavior here.

Extreme Mass-Ratio Inspirals

An Extreme Mass-Ratio Inspiral (Inspiral: The gradually-shrinking orbit of a binary system. As the pair of stars in the binary orbit each other, they give off energy in the form of gravitational waves. This lost energy draws them closer in their orbit — eventually resulting in a Merger.) (Extreme Mass-Ratio Inspiral: A particular type of binary in which there is a very large difference in the masses of the two objects. Generally, this will involve a super-massive Black Hole with a mass millions of times that of our Sun, and a Neutron Star (Neutron Star: A type of star which is very old, having cooled off and stopped nuclear fusion reactions. When gravity pulls the star down on itself, the electrons and protons are squeezed together, leaving just neutrons. The star is then supported against gravity by "neutron degeneracy pressure" (no two neutrons can be in the same place at the same time). These are produced when a star is too heavy to be a white dwarf, but not heavy enough to turn into a Black Hole. ) or Black Hole with a mass roughly the same as our Sun.) is a particular type of Compact Binary. In this pairing, one member is millions of times more massive than the other. This is a particularly "clean" example of an binary, meaning that it is very well understood. The inspiral also takes a very long time. This will allow physicists to make very careful observations of the system.

Collapsing Stars and Supernovae (Supernova: Violently exploding stars which shine very brightly for days or weeks. They occur when the fuel for nuclear reactions is used up, and a star cools. Gravity pulls all the matter down toward the star's center. If this happens quickly, nuclear reactions may suddenly begin again, detonating the star in a nuclear explosion. )})

The violence of a supernova (Supernova: Violently exploding stars which shine very brightly for days or weeks. They occur when the fuel for nuclear reactions is used up, and a star cools. Gravity pulls all the matter down toward the star's center. If this happens quickly, nuclear reactions may suddenly begin again, detonating the star in a nuclear explosion. ) may provide the tremendous warping of spacetime necessary to give off gravitational waves. If so, the sound would be very brief. This type of wave is called a "burst". Because supernovae are so powerful, and happen so quickly, the gravitational waves should also be very powerful.

The First Moments

Exotic Possibilities

Detector Sounds

Gravitational Wave (Gravitational Wave: A gravitational disturbance that travels through space like a wave. This type of wave is analogous to an Electromagnetic Wave. Gravitational waves are given off by most movements of anything with mass. Usually, however, they are quite difficult to detect. Physicists are currently working hard to directly detect gravitational waves. Experiments like LIGO and LISA are designed for this purpose. ) Detectors are designed to be extraordinarily sensitive to the tiniest motions of their components. Nothing on Earth can be truly isolated from the rest of the Earth, however, which means that any detector's components will be moving. This will produce a great deal of noise noise in the detector's output. Things like earthquakes, and trucks rumbling along nearby highways will produce deep-pitched noise. Just as importantly, lack of laser power will produce high-pitched noise.