What is a gravitational wave?

The official opening day (detection) of gravitational waves is February 11, 2016. Just then, at a press conference in Washington, the leaders of the LIGO collaboration announced that the research team was able to record this phenomenon for the first time in the history of mankind.

Prophecies of the great Einstein

Albert Einstein suggested that gravitational waves exist at the beginning of the last century (1916) within the framework of the General Relativity (GRT) formulated by him. It remains only to be amazed at the genius abilities of the famous physicist, who, with a minimum of real data, was able to draw such far-reaching conclusions. Among the many other predicted physical phenomena that have been confirmed in the next century (slowing down the flow of time, changing the direction of electromagnetic radiation in gravitational fields, etc.), it was not possible to practically detect the presence of this type of wave interaction of bodies until recently.

Gravity is an illusion?

Generally, in the light of the Theory of Relativity, gravity is hard to call a force. This is a consequence of the perturbation or curvature of the space-time continuum. A good example, illustrating this postulate, can serve as a stretched piece of tissue. Under the weight of a massive object placed on such a surface, a depression is formed. Other objects moving near this anomaly will change the trajectory of their movement, as if "attracting". And the more the weight of the object (the greater the diameter and depth of curvature), the higher the "force of attraction". When it moves along the fabric, one can observe the appearance of a divergent "ripple".

Something similar happens in the world space. Any accelerated moving massive matter is a source of fluctuations in the density of space and time. Gravitational wave with a significant amplitude, is formed by bodies with extremely large masses or when moving with huge accelerations.

physical characteristics

The oscillations of the space-time metric manifest themselves as changes in the gravitational field. This phenomenon is also called space-time ripples. The gravitational wave affects the bodies and objects encountered, compressing and stretching them. The values of the deformation are very insignificant - of the order of 10 ^-21 of the original size. The whole difficulty of discovering this phenomenon was that the researchers needed to learn how to measure and record such changes with the help of appropriate equipment. The power of gravitational radiation is also extremely small - for the entire solar system it is several kilowatts.

The speed of propagation of gravitational waves is insignificantly dependent on the properties of the conducting medium. The amplitude of the oscillations with the distance from the source gradually decreases, but never reaches zero. The frequency lies in the range from a few tens to hundreds of hertz. The speed of gravitational waves in the interstellar medium is approaching the speed of light.

Indirect evidence

For the first time the theoretical confirmation of the existence of gravity waves was obtained by the American astronomer Joseph Taylor and his assistant Russell Huls in 1974. Exploring the expanses of the Universe with the radio telescope of the Arecibo Observatory (Puerto Rico), the researchers discovered the pulsar PSR B1913 + 16, which is a double system of neutron stars revolving around a common center of mass with a constant angular velocity (a fairly rare case). Annually, the circulation period, which is initially 3.75 hours, is reduced by 70 ms. This value completely corresponds to the conclusions from the equations of general relativity, which predict an increase in the rotation speed of such systems as a result of the expenditure of energy on the generation of gravitational waves. Later, several double pulsars and white dwarfs with similar behavior were detected. To radio astronomers D. Taylor and R. Hals in 1993 was awarded the Nobel Prize in Physics for the discovery of new opportunities for studying gravitational fields.

The escaping gravitational wave

The first statement on the detection of gravity waves came from the scientist of Maryland University, Joseph Weber (USA) in 1969. For this purpose, he used two gravitational antennas of his own design, spaced two kilometers apart. The resonant detector was a well-vibro-isolated one-meter two-meter cylinder made of aluminum, equipped with sensitive piezoelectric sensors. The amplitude allegedly fixed by Weber oscillations was more than a million times higher than the expected value. Attempts by other scientists using similar equipment to repeat the "success" of the American physicist did not bring positive results. A few years later, Weber's work in this area was recognized as untenable, but gave rise to the development of a "gravitational boom" that attracted many specialists to this field of research. By the way, Joseph Weber himself until the end of his days was sure that he was taking gravitational waves.

Improvement of receiving equipment

In the 70s, scientist Bill Fairbank (USA) developed the design of a gravitational wave antenna cooled with liquid helium using SQUIDs - ultrasensitive magnetometers. The existing technologies at that time did not allow the inventor to see his product realized in the "metal".

By this principle, the Auriga gravitational detector is made at the National Lloyary Laboratory (Padua, Italy). The design is based on an aluminum-magnesium cylinder, 3 meters long and 0.6 m in diameter. The receiving device weighing 2.3 tons is suspended in an isolated vacuum chamber that has been cooled almost to absolute zero. To fix and detect jitters, an auxiliary kilogram resonator and a computer-based measuring system are used. Declared sensitivity of the equipment is 10 ^-20 .

Interferometers

The basis for the operation of interference detectors for gravitational waves is the same as the principles used by the Michelson interferometer. The laser beam emitted by the source is divided into two streams. After multiple reflections and travels along the shoulders of the device, the streams are brought together again, and judging by the resulting interference image, it is judged whether any perturbations (for example, a gravitational wave) affected the path of the rays. Similar equipment has been created in many countries:

• GEO 600 (Hannover, Germany). The length of the vacuum tunnels is 600 meters.
• TAMA (Japan) with shoulders at 300 m.
• VIRGO (Pisa, Italy) is a joint Franco-Italian project launched in 2007 with three kilometer tunnels.
• LIGO (USA, Pacific Coast), leading the hunt for gravity waves since 2002.

The latter should be considered in more detail.

LIGO Advanced

The project was created on the initiative of scientists from Massachusetts and California technological institutes. Includes two observatories, separated by 3 thousand km, in the states of Louisiana and Washington (the cities of Livingston and Hanford) with three identical interferometers. The length of perpendicular vacuum tunnels is 4 thousand meters. These are the largest existing such structures at the moment. Until 2011, numerous attempts to detect gravity waves did not bring any results. The conducted significant modernization (Advanced LIGO) increased the sensitivity of equipment in the 300-500 Hz range by more than five times, and in the low-frequency region (up to 60 Hz) by almost an order of magnitude, reaching such a coveted value of 10 ^-21 . The updated project started in September 2015, and the efforts of more than a thousand collaborators were rewarded with the results.

Gravitational waves are detected

September 14, 2015 improved LIGO detectors with an interval of 7 ms recorded the gravitational waves that came to our planet from the largest phenomenon that occurred on the outskirts of the observed universe - the fusion of two large black holes with masses 29 and 36 times the mass of the Sun. In the course of the process, which took place over 1.3 billion years ago, about three solar masses of matter were consumed for radiation of gravity waves in a fraction of a second. The fixed initial frequency of gravitational waves was 35 Hz, and the maximum peak value reached 250 Hz.

The results obtained were repeatedly subjected to comprehensive verification and processing, and alternative interpretations of the obtained data were carefully cut off. Finally, on 11 February last year, a direct registration of the phenomenon predicted by Einstein was announced to the world community.

The fact that illustrates the titanic work of researchers: the amplitude of the oscillations of the dimensions of the arms of the interferometers was 10 ^-19 m - this value is as much less than the diameter of the atom, when it is less than the orange itself.

Further perspectives

This discovery once again confirms that the General Theory of Relativity is not just a collection of abstract formulas, but a fundamentally new view of the essence of gravitational waves and gravity as a whole.

In further research, scientists pin great hopes on the ELSA project: the creation of a giant orbital interferometer with shoulders of about 5 million km, capable of detecting even minor perturbations of the gravitational fields. Activation of works in this direction is able to tell a lot about the main stages of the development of the universe, about the processes, whose observation in traditional ranges is difficult or impossible. Undoubtedly, black holes, whose gravitational waves will be fixed in the future, will tell a lot about their nature.

To study the relic gravitational radiation that can tell about the first moments of our world after the Big Bang, more sensitive space instruments will be needed. ), но его реализация, по заверениям специалистов, возможна не ранее, чем через 30-40 лет. Such a project exists ( Big Bang Observer ), but its implementation, according to experts, is possible not earlier than in 30-40 years.