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Gravitational waves of the universe

Gravitational waves of the universe (Picture 1)

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In physics, gravitational waves refer to the ripples in the curvature of space-time, which propagate outward from the radiation source in the form of waves, which transmit energy in the form of gravitational radiation. In 1916, Einstein predicted the existence of gravitational waves based on general relativity. The existence of gravitational waves is the result of Lorentz invariance of general relativity, because it introduces the concept of limited propagation speed of interaction. In contrast, gravitational waves cannot exist in Newton's classical theory of gravity, because Newton's classical theory assumes that the interaction and propagation of matter is infinite speed.

In Einstein's general theory of relativity, gravity is considered to be an effect of the curvature of time and space. This bending is caused by the presence of mass. Generally speaking, in a given volume, the greater the mass contained, the greater the curvature of space-time caused at the boundary of this volume. When a mass object moves in space and time, the change in curvature reflects the change in the position of these objects. Under certain circumstances, accelerating objects can change this curvature and propagate outward in the form of waves at the speed of light. This kind of propagation phenomenon is called gravitational wave, and it can also be understood as: the gravitational force generated by a massive celestial body affects celestial bodies smaller than it in a certain range, causing them to produce negative acceleration, and the curvature formed by their trajectory The phenomenon of getting bigger and releasing energy. Derived from Kepler's law: the speed of an object's motion is inversely proportional to the curvature formed by its trajectory.

So in our universe, what kind of celestial bodies can shake and produce detectable gravitational waves? It is generally considered that there are the following:

(1) In-spiral or merged compact star binary system. For example, the binary star system of neutron stars or black holes.

(2) Fast rotating dense celestial bodies. This type of celestial body will lose angular momentum through periodic gravitational wave radiation, and its signal strength will increase as the degree of asymmetry increases. Possible candidates include asymmetric neutron stars and the like.

(3) Random gravitational wave background. It is very similar to the cosmic background radiation that we are usually familiar with. This type of background gravitational wave, also usually called the primordial gravitational wave, is a relic of the early universe when it was inflated.

(4) Supernovae or gamma-ray bursts erupt. The asymmetry dynamics of a star explodes can also produce gravitational waves. The direct detection of gravitational waves from these celestial bodies will provide the most direct and innermost information on these celestial bodies.

(5) In some galaxies, there will be two black holes. It is very similar to the double star-shaped black hole detected by LIGO. When the two double black holes revolve and finally merge, they will also generate strong gravitational waves.

A variety of gravitational wave detectors are being built or in operation, such as advanced LIGO, which has been in operation since September 2015. Possible sources of gravitational wave detection include compact binary star systems (white dwarfs, neutron stars, and black holes). On February 11, 2016, the LIGO Scientific Cooperation Organization and the Virgo team announced that they had used advanced LIGO detectors to detect gravitational wave signals from the merger of two black holes for the first time. In the early morning of June 16, 2016, the LIGO cooperation team announced: On December 26, 2015, two gravitational wave detectors located in the Hanford District of the United States and Livingston, Louisiana, simultaneously detected a gravitational wave signal; this It is the second gravitational wave signal detected by humans after the first gravitational wave signal detected by LIGO on September 14, 2015. On October 16, 2017, scientists from many countries around the world held a press conference simultaneously, announcing that for the first time, human beings directly detected gravitational waves from the merger of binary neutron stars and "seeing" the electromagnetic signals emitted by this spectacular cosmic event at the same time.

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