# Gravitational waves

Some equations formulated by Einstein in 1915 predicted the existence of a phenomenon called gravitational waves. At the end of 2015 these waves were detected directly.

We all know what the waves are. For example, those that form in a pond with still water when a stone is thrown.

In the Theory of relativity, Einstein demonstrates that space and time are not independent of each other, but constitute a unique entity called space time. If we imagine these two variables together forming a two-dimensional flat elastic membrane, we can guess that, in the presence of a mass, spacetime will "deform", as a normal membrane would do under the weight of a billiard ball.

Any other object with mass notices that deformation, and is forced to follow different paths than it would follow if the membrane were not deformed. The effect or consequence of that curved geometry of spacetime is the gravity, and this is how relativity manages to explain the famous universal gravitation discovered by Newton.

## How do gravitational waves occur?

Accelerated massive bodies produce fluctuations in the space-time fabric that propagates like a wave throughout the Universe. These are the gravitational waves planned by Einstein and now discovered.

Only exceptional events in cosmic objects with huge masses, such as neutron stars, gamma-ray bursts or black holes, can produce waves with enough energy to be detected; events as powerful as, for example, the explosion of a giant supernova or the fusion of two black holes.

Gravitational waves shorten space-time in one direction, lengthen it in the other, and propagate at the speed of light. Nothing stops or reflects them; Therefore, unlike light and other electromagnetic waves, it hardly matters how many objects they find in their path until they reach Earth.

Because they are important? Some events in the Universe are very difficult to detect directly. For example, observe black holes, which do not emit light. However, they can emit gravitational waves at times, such as when two of them collide and merge. This is what happened the first time gravitational waves were detected. They may even explain to us what happened in the first second of the Universe, just after the big Bang. It is hoped that this discovery will help to understand some of the great unknowns that physics and astronomy still have in mind.

## How are they detected?

The Advanced Observatory of Gravitational Wave Laser Interferometry, known as LIGO, consisted of two detectors separated by 3,000 kilometers in 2015, in the states of Washington and Louisiana. Each detector consisted of two beams of laser light four kilometers long, arranged at right angles. When a gravitational wave occurs, one of these beams of light lengthens, while the other shortens. LIGO can detect differences of one ten thousandth of the diameter of an atomic nucleus.

The first signal was captured on September 14 at the two detectors at the same time. It came from a merger at 1.3 billion light-years and consisted of the collision of two black holes whose mass was 29 and 36 times that of the Sun. The two holes merged into one, releasing an energy equivalent to three solar masses , which was dismissed in the form of gravitational waves. When these waves reached us, 1.3 billion years later, they produced a very slight disturbance of space-time, imperceptible to everyone, but enough for the very high sensitivity of LIGO.

Scientists Rainer Weiss, Barry Barish and Kip Thorne won the 2017 Nobel Prize in Physics for their work on LIGO, the gravitational wave detector. The jury has recognized them for a discovery that shook the world. The three American physicists also received the Princess of Asturias Award for their decisive work in capturing this phenomenon with the Gravitational Wave Laser Interferometry Observatory.

The UIB Group of Relativity and Gravitation is a pioneer in Spain in the study of gravitational waves. In your page The Symphony of the Universe They offer information and resources on this subject.

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