We now live in a Universe filled with gravitational waves.

Until Thursday morning's historic announcement from the National Science Foundation (NSF) meeting in Washington, there were only rumors that the Laser Interferometer Gravitational-Wave Observatory (LIGO) had discovered a key component of Albert Einstein's General Theory of Relativity, but now we know the reality is deeper. than we thought.

With amazing clarity, LIGO was able to “hear” the moment before a binary system (two black holes orbiting each other) merged into a single whole, creating a gravitational wave signal so clear in accordance with the theoretical model that it did not require discussion. LIGO witnessed the “rebirth” of a powerful black hole that happened about 1.3 billion years ago.

Gravitational waves have always been and will always be passing through our planet (indeed, passing through us), but only now do we know how to find them. We have now opened our eyes to various cosmic signals, vibrations caused by known energetic events, and are witnessing the birth of a completely new area astronomy.

The sound of two black holes merging:

“We can now hear the Universe,” said Gabriela Gonzalez, a physicist and LIGO spokeswoman, during Thursday’s triumphant meeting. “The discovery marks the beginning of new era: The field of gravitational astronomy is now a reality."

Our place in the Universe is changing greatly and this discovery could be as fundamental as the discovery of radio waves and the understanding that the Universe is expanding.

The Theory of Relativity Becomes More Valuable

Trying to explain what gravitational waves are and why they are so important is as complex as the equations that describe them, but their discovery not only strengthens Einstein's theories about the nature of space-time, we now have a tool for probing parts of the universe that were invisible to everyone. us. We can now study cosmic waves created by the most energetic events occurring in the Universe, and perhaps use gravitational waves to make new physical discoveries and explore new astronomical phenomena.

“Now we have to prove that we have the technology to go beyond discovery gravitational waves"It opens up a lot of possibilities," Lewis Lehner of the Institute of Theoretical Physics in Ontario said in an interview after Thursday's announcement.

Lehner's research focuses on dense objects (such as black holes) that create powerful gravitational waves. Although not associated with the LIGO collaboration, Lehner quickly realized the importance of this historic discovery. “There are no better signals,” he said.

The discovery is based on three paths, he reasons. First, we now know that gravitational waves exist, and we know how to detect them. Secondly, the signal detected by LIGO stations on September 14, 2015 is strong evidence of the existence of a binary system of black holes, and each black hole weighs several tens of solar masses. The signal is exactly what we expected to see from the violent merger of two black holes, one weighing 29 times the Sun, the other 36 times. Third, and perhaps most important, “the ability to be sent into a black hole” is by far the strongest evidence for the existence of black holes.

Cosmic intuition

This event was accompanied by luck, like many other scientific discoveries. LIGO is the largest project funded by the National Science Foundation, which originally started in 2002. It turned out that after many years of searching for the elusive signal of gravitational waves, LIGO was not sensitive enough and in 2010 the observatories were frozen while international cooperation was carried out to increase their sensitivity. Five years later, in September 2015, the “improved LIGO” was born.

At the time, LIGO co-founder and theoretical physics heavyweight Kip Thorne was confident of LIGO's success, telling the BBC: "We're here. We got to the field great game. And it is quite clear that we will lift the veil of secrecy.” - And he was right, a few days after the reconstruction, a burst of gravitational waves swept across our planet, and LIGO was sensitive enough to detect them.

These black hole mergers are not considered anything special; It is estimated that such events occur every 15 minutes somewhere in the Universe. But this particular merger occurred in the right place (1.3 billion light-years away) at the right time (1.3 billion years ago) for the LIGO observatories to pick up its signal. It was a pure signal from the Universe, and Einstein predicted it, and its gravitational waves turned out to be real, describing a cosmic event 50 times more powerful than the power of all the stars in the Universe combined. This huge burst of gravitational waves was recorded by LIGO as a high-frequency signal with linear frequency modulation as the black holes spiraled together and merged into one.

To confirm the propagation of gravitational waves, LIGO consists of two observing stations, one in Louisiana, the other in Washington. To eliminate false alarms, the gravitational wave signal must be detected at both stations. On September 14, the result was obtained first in Louisiana, and 7 milliseconds later in Washington. The signals coincided, and with the help of triangulation, physicists were able to find out that they originated in the celestial space of the Southern Hemisphere.

Gravitational waves: how can they be useful?

So we have confirmation of a black hole merger signal, but so what? This historical discovery, which is quite understandable - 100 years ago Einstein could not even dream of discovering these waves, but it still happened.

General relativity was one of the most profound scientific and philosophical insights of the 20th century and forms the basis of some of the most intelligent research in reality. In astronomy, the applications of general relativity are clear: from the gravitational lens to measuring the expansion of the Universe. But it's not at all clear practical use Einstein's theories, but most modern technology uses lessons from relativity in some things that are considered simple. For example, take global navigation satellites, they will not be accurate enough unless a simple adjustment to time dilation (predicted by relativity) is applied.

It is clear that general relativity has applications in the real world, but when Einstein presented his theory in 1916, its application was highly questionable, which seemed obvious. He simply connected the Universe into the way he saw it, and that’s how it was born general theory relativity. And now another component of the theory of relativity has been proven, but how can gravitational waves be used? Astrophysicists and cosmologists are definitely intrigued.

“Once we have collected data from pairs of black holes that will act as beacons scattered throughout the universe,” theoretical physicist Neil Turok, director of the Institute for Theoretical Physics, said Thursday during a video presentation. “We will be able to measure the speed.” expansion of the Universe, or the amount of dark energy with extreme precision, much more accurately than we can today."

“Einstein developed his theory with some clues from nature, but based on logical consistency. After 100 years, you see very accurate confirmation of his predictions."

Moreover, the September 14 event has some physics features that still need to be explored. For example, Lehner noted that from analyzing the gravitational wave signal, it is possible to measure the "spin" or angular momentum of a merging black hole. "If you've been working on the theory for a long time, you'll know that the black hole has a very, very special spin," he said.

The formation of gravitational waves during the merger of two black holes:

For some reason, the final rotation of the black hole is slower than expected, indicating that the black holes collided at low speed, or they were in such a collision that caused a joint angular momentum opposing each other. "It's very interesting, why did nature do this?" Lehner said.

This recent mystery may bring back some basic physics that had been left out, but, more intriguingly, it may reveal “new,” unusual physics that doesn't fit into general relativity. And this highlights other uses for gravitational waves: since they are created by strong gravitational phenomena, we have the ability to probe this environment from afar, with possible surprises along the way. In addition, we could combine observations of astrophysical phenomena with electromagnetic forces to better understand the structure of the Universe.

Application?

Naturally, after huge announcements made from a set of scientific discoveries, many people outside the scientific community are wondering how they might be affected. The depth of the discovery may be lost, which certainly applies to gravitational waves. But consider another case, when Wilhelm Roentgen discovered X-rays in 1895, during experiments with cathode ray tubes, few people know that only a few years later, these electromagnetic waves will become a key component in everyday medicine from diagnosis to treatment. Likewise, with the first experimental creation of radio waves in 1887, Heinrich Hertz confirmed the famous electromagnetic equations of James Clerk Maxwell. Only after a while in the 90s of the 20th century, Guglielmo Marconi, who created a radio transmitter and radio receiver, proved their practical application. Also, Schrödinger's equations, which describe the complex world of quantum dynamics, are now being used in the development of ultra-fast quantum computing.

All scientific discoveries are useful, and many ultimately have everyday applications that we take for granted. Currently, the practical applications of gravitational waves are limited to astrophysics and cosmology - we now have a window into the “dark universe”, invisible to electromagnetic radiation. Without a doubt, scientists and engineers will find other uses for these cosmic pulsations besides probing the Universe. However, to detect these waves, there must be good progress in optical engineering at LIGO, in which new technologies will appear over time.

Gravitational waves - artist's rendering

Gravitational waves are disturbances of the space-time metric that break away from the source and propagate like waves (the so-called “space-time ripples”).

In general relativity and most others modern theories In gravity, gravitational waves are generated by the motion of massive bodies with variable acceleration. Gravitational waves propagate freely in space at the speed of light. Due to the relative weakness gravitational forces(compared to others) these waves have a very small magnitude, which is difficult to register.

Polarized gravitational wave

Gravitational waves are predicted by the general theory of relativity (GR), and many others. They were first directly detected in September 2015 by two twin detectors, which detected gravitational waves, likely resulting from the merger of two and the formation of one more massive rotating black hole. Indirect evidence of their existence has been known since the 1970s - General Relativity predicts the rate of convergence of close systems due to the loss of energy due to the emission of gravitational waves, which coincides with observations. Direct registration of gravitational waves and their use to determine the parameters of astrophysical processes is an important task of modern physics and astronomy.

Within the framework of general relativity, gravitational waves are described by solutions of wave-type Einstein equations, which represent a perturbation of the space-time metric moving at the speed of light (in the linear approximation). The manifestation of this disturbance should be, in particular, a periodic change in the distance between two freely falling (that is, not influenced by any forces) test masses. Amplitude h gravitational wave is a dimensionless quantity - a relative change in distance. The predicted maximum amplitudes of gravitational waves from astrophysical objects (for example, compact binary systems) and phenomena (explosions, mergers, captures by black holes, etc.) when measured are very small ( h=10 −18 -10 −23). A weak (linear) gravitational wave, according to the general theory of relativity, transfers energy and momentum, moves at the speed of light, is transverse, quadrupole and is described by two independent components located at an angle of 45° to each other (has two directions of polarization).

Different theories predict the speed of propagation of gravitational waves differently. In general relativity, it is equal to the speed of light (in the linear approximation). In other theories of gravity, it can take any value, including infinity. According to the first registration of gravitational waves, their dispersion turned out to be compatible with a massless graviton, and the speed was estimated to be equal to the speed of light.

Generation of gravitational waves

A system of two neutron stars creates ripples in space-time

A gravitational wave is emitted by any matter moving with asymmetric acceleration. For a wave of significant amplitude to occur, an extremely large mass of the emitter and/or enormous accelerations are required; the amplitude of the gravitational wave is directly proportional first derivative of acceleration and the mass of the generator, that is ~ . However, if an object is moving at an accelerated rate, this means that some force is acting on it from another object. In turn, this other object experiences the opposite effect (according to Newton’s 3rd law), and it turns out that m 1 a 1 = − m 2 a 2 . It turns out that two objects emit gravitational waves only in pairs, and as a result of interference they are mutually canceled out almost completely. Therefore, gravitational radiation in the general theory of relativity always has the multipole character of at least quadrupole radiation. In addition, for non-relativistic emitters in the expression for the radiation intensity there is a small parameter where is the gravitational radius of the emitter, r- his characteristic size, T- characteristic period of movement, c- speed of light in vacuum.

The strongest sources of gravitational waves are:

• colliding (giant masses, very small accelerations),
• gravitational collapse dual system compact objects (colossal accelerations with a fairly large mass). As a special and most interesting case - the merger of neutron stars. In such a system, the gravitational-wave luminosity is close to the maximum Planck luminosity possible in nature.

Gravitational waves emitted by a two-body system

Two bodies moving in circular orbits around a common center of mass

Two gravitationally bound bodies with masses m 1 and m 2, moving non-relativistically ( v << c) in circular orbits around their common center of mass at a distance r from each other, emit gravitational waves of the following energy, on average over the period:

As a result, the system loses energy, which leads to the convergence of bodies, that is, to a decrease in the distance between them. Speed ​​of approach of bodies:

For the Solar System, for example, the greatest gravitational radiation is produced by the and subsystem. The power of this radiation is approximately 5 kilowatts. Thus, the energy lost by the Solar System to gravitational radiation per year is completely negligible compared to the characteristic kinetic energy of bodies.

Gravitational collapse of a binary system

Any double star, when its components rotate around a common center of mass, loses energy (as assumed - due to the emission of gravitational waves) and, in the end, merges together. But for ordinary, non-compact, double stars, this process takes a very long time, much longer than the present age. If a compact binary system consists of a pair of neutron stars, black holes, or a combination of both, then the merger can occur within several million years. First, the objects come closer together, and their period of revolution decreases. Then, at the final stage, a collision and asymmetric gravitational collapse occurs. This process lasts a fraction of a second, and during this time energy is lost into gravitational radiation, which, according to some estimates, amounts to more than 50% of the mass of the system.

Basic exact solutions of Einstein's equations for gravitational waves

Bondi-Pirani-Robinson body waves

These waves are described by a metric of the form . If we introduce a variable and a function, then from the general relativity equations we obtain the equation

Takeno Metric

has the form , -functions satisfy the same equation.

Rosen metric

Where to satisfy

Perez metric

Wherein

Cylindrical Einstein-Rosen waves

In cylindrical coordinates, such waves have the form and are executed

Registration of gravitational waves

Registration of gravitational waves is quite difficult due to the weakness of the latter (small distortion of the metric). The devices for registering them are gravitational wave detectors. Attempts to detect gravitational waves have been made since the late 1960s. Gravitational waves of detectable amplitude are born during the collapse of a binary. Similar events occur in the surrounding area approximately once a decade.

On the other hand, the general theory of relativity predicts the acceleration of the mutual rotation of binary stars due to the loss of energy in the emission of gravitational waves, and this effect is reliably recorded in several known systems of binary compact objects (in particular, pulsars with compact companions). In 1993, “for the discovery of a new type of pulsar, which provided new opportunities in the study of gravity” to the discoverers of the first double pulsar PSR B1913+16, Russell Hulse and Joseph Taylor Jr. was awarded the Nobel Prize in Physics. The acceleration of rotation observed in this system completely coincides with the predictions of general relativity for the emission of gravitational waves. The same phenomenon was recorded in several other cases: for the pulsars PSR J0737-3039, PSR J0437-4715, SDSS J065133.338+284423.37 (usually abbreviated J0651) and the system of binary RX J0806. For example, the distance between the two components A and B of the first binary star of the two pulsars PSR J0737-3039 decreases by about 2.5 inches (6.35 cm) per day due to energy loss to gravitational waves, and this occurs in agreement with general relativity . All these data are interpreted as indirect confirmation of the existence of gravitational waves.

According to estimates, the strongest and most frequent sources of gravitational waves for gravitational telescopes and antennas are catastrophes associated with the collapse of binary systems in nearby galaxies. It is expected that in the near future several similar events per year will be recorded on improved gravitational detectors, distorting the metric in the vicinity by 10 −21 -10 −23 . The first observations of an optical-metric parametric resonance signal, which makes it possible to detect the effect of gravitational waves from periodic sources such as a close binary on the radiation of cosmic masers, may have been obtained at the radio astronomical observatory of the Russian Academy of Sciences, Pushchino.

Another possibility of detecting the background of gravitational waves filling the Universe is high-precision timing of distant pulsars - analysis of the arrival time of their pulses, which characteristically changes under the influence of gravitational waves passing through the space between the Earth and the pulsar. Estimates for 2013 indicate that timing accuracy needs to be improved by about one order of magnitude to detect background waves from multiple sources in our Universe, a task that could be accomplished before the end of the decade.

According to modern concepts, our Universe is filled with relic gravitational waves that appeared in the first moments after. Their registration will make it possible to obtain information about the processes at the beginning of the birth of the Universe. On March 17, 2014 at 20:00 Moscow time at the Harvard-Smithsonian Center for Astrophysics, an American group of researchers working on the BICEP 2 project announced the detection of non-zero tensor disturbances in the early Universe by the polarization of the cosmic microwave background radiation, which is also the discovery of these relict gravitational waves . However, almost immediately this result was disputed, since, as it turned out, the contribution was not properly taken into account. One of the authors, J. M. Kovats ( Kovac J. M.), admitted that “the participants and science journalists were a bit hasty in interpreting and reporting the data from the BICEP2 experiment.”

Experimental confirmation of the existence

The first recorded gravitational wave signal. On the left is data from the detector in Hanford (H1), on the right - in Livingston (L1). Time is counted from September 14, 2015, 09:50:45 UTC. To visualize the signal, it is filtered with a frequency filter with a passband of 35-350 Hertz to suppress large fluctuations outside the high sensitivity range of the detectors; band-stop filters were also used to suppress the noise of the installations themselves. Top row: voltages h in the detectors. GW150914 first arrived at L1 and 6 9 +0 5 −0 4 ms later to H1; For visual comparison, data from H1 are shown in the L1 graph in reversed and time-shifted form (to account for the relative orientation of the detectors). Second row: voltages h from the gravitational wave signal, passed through the same 35-350 Hz bandpass filter. The solid line is the result of numerical relativity for a system with parameters compatible with those found based on the study of the GW150914 signal, obtained by two independent codes with a resulting match of 99.9. The gray thick lines are the 90% confidence regions of the waveform reconstructed from the detector data by two different methods. The dark gray line models the expected signals from the merger of black holes, the light gray line does not use astrophysical models, but represents the signal as a linear combination of sinusoidal-Gaussian wavelets. The reconstructions overlap by 94%. Third row: Residual errors after extracting the filtered prediction of the numerical relativity signal from the filtered signal of the detectors. Bottom row: A representation of the voltage frequency map, showing the increase in the dominant frequency of the signal over time.

February 11, 2016 by the LIGO and VIRGO collaborations. The merger signal of two black holes with an amplitude at maximum of about 10 −21 was recorded on September 14, 2015 at 9:51 UTC by two LIGO detectors in Hanford and Livingston, 7 milliseconds apart, in the region of maximum signal amplitude (0.2 seconds) combined the signal-to-noise ratio was 24:1. The signal was designated GW150914. The shape of the signal matches the prediction of general relativity for the merger of two black holes with masses of 36 and 29 solar masses; the resulting black hole should have a mass of 62 solar and a rotation parameter a= 0.67. The distance to the source is about 1.3 billion, the energy emitted in tenths of a second in the merger is the equivalent of about 3 solar masses.

Story

The history of the term “gravitational wave” itself, the theoretical and experimental search for these waves, as well as their use for studying phenomena inaccessible to other methods.

• 1900 - Lorentz suggested that gravity “...can spread at a speed no greater than the speed of light”;
• 1905 - Poincaré first introduced the term gravitational wave (onde gravifique). Poincaré, on a qualitative level, removed the established objections of Laplace and showed that the corrections associated with gravitational waves to the generally accepted Newtonian laws of gravity of order cancel, thus the assumption of the existence of gravitational waves does not contradict observations;
• 1916 - Einstein showed that, within the framework of general relativity, a mechanical system will transfer energy to gravitational waves and, roughly speaking, any rotation relative to fixed stars must sooner or later stop, although, of course, under normal conditions, energy losses of the order of magnitude are negligible and practically not measurable (in In this work, he also mistakenly believed that a mechanical system that constantly maintains spherical symmetry can emit gravitational waves);
• 1918 - Einstein derived a quadrupole formula in which the emission of gravitational waves turns out to be an effect of order , thereby correcting the error in his previous work (an error remained in the coefficient, the wave energy is 2 times less);
• 1923 - Eddington - questioned the physical reality of gravitational waves "...propagating...at the speed of thought." In 1934, when preparing the Russian translation of his monograph “The Theory of Relativity,” Eddington added several chapters, including chapters with two options for calculating energy losses by a rotating rod, but noted that the methods used for approximate calculations of general relativity, in his opinion, are not applicable to gravitationally bound systems , so doubts remain;
• 1937 - Einstein, together with Rosen, investigated cylindrical wave solutions to the exact equations of the gravitational field. During the course of these studies, they began to doubt that gravitational waves may be an artifact of approximate solutions of the general relativity equations (correspondence regarding a review of the article “Do gravitational waves exist?” by Einstein and Rosen is known). Later, he found an error in his reasoning; the final version of the article with fundamental changes was published in the Journal of the Franklin Institute;
• 1957 - Herman Bondi and Richard Feynman proposed the “beaded cane” thought experiment in which they substantiated the existence of physical consequences of gravitational waves in general relativity;
• 1962 - Vladislav Pustovoit and Mikhail Herzenstein described the principles of using interferometers to detect long-wave gravitational waves;
• 1964 - Philip Peters and John Matthew theoretically described gravitational waves emitted by binary systems;
• 1969 - Joseph Weber, founder of gravitational wave astronomy, reports the detection of gravitational waves using a resonant detector - a mechanical gravitational antenna. These reports give rise to a rapid growth of work in this direction, in particular, Rainier Weiss, one of the founders of the LIGO project, began experiments at that time. To date (2015), no one has been able to obtain reliable confirmation of these events;
• 1978 - Joseph Taylor reported the detection of gravitational radiation in the binary pulsar system PSR B1913+16. Joseph Taylor and Russell Hulse's research earned them the 1993 Nobel Prize in Physics. As of early 2015, three post-Keplerian parameters, including period reduction due to gravitational wave emission, had been measured for at least 8 such systems;
• 2002 - Sergey Kopeikin and Edward Fomalont used ultra-long-baseline radio wave interferometry to measure the deflection of light in the gravitational field of Jupiter in dynamics, which for a certain class of hypothetical extensions of general relativity makes it possible to estimate the speed of gravity - the difference from the speed of light should not exceed 20% (this interpretation does not generally accepted);
• 2006 - the international team of Martha Bourgay (Parkes Observatory, Australia) reported significantly more accurate confirmation of general relativity and its correspondence to the magnitude of gravitational wave radiation in the system of two pulsars PSR J0737-3039A/B;
• 2014 - Astronomers at the Harvard-Smithsonian Center for Astrophysics (BICEP) reported the detection of primordial gravitational waves while measuring fluctuations in the cosmic microwave background radiation. At the moment (2016), the detected fluctuations are considered not to be of relict origin, but are explained by the emission of dust in the Galaxy;
• 2016 - international LIGO team reported the detection of the gravitational wave transit event GW150914. For the first time, direct observation of interacting massive bodies in ultra-strong gravitational fields with ultra-high relative velocities (< 1,2 × R s , v/c >0.5), which made it possible to verify the correctness of general relativity with an accuracy of several post-Newtonian terms of high orders. The measured dispersion of gravitational waves does not contradict previously made measurements of the dispersion and upper bound on the mass of a hypothetical graviton (< 1,2 × 10 −22 эВ), если он в некотором гипотетическом расширении ОТО будет существовать.



Participants in the LIGO scientific experiment, in which Russian physicists are also participating, announced that American observatories have detected gravitational waves generated by the collision of two black holes.

Gravitational waves were recorded on September 14, 2015, which was reported on February 11, 2016 at a special press conference by LIGO representatives in Washington. It took scientists six months to process and verify the results. This can be considered the official discovery of gravitational waves, since they were directly recorded on Earth for the first time. The results of the work were published in the journal Physical Review Letters.

Physicists from Moscow State University at a press conference. Photo by Maxim Abaev.

Diagram of interferometers and their location on a schematic map of the United States. The test mirror masses in the figure are called Test Mass.

Test masses, also known as interferometer mirrors, are made of fused quartz. Photo: www.ligo.caltech.edu

Numerical simulation of gravitational waves from approaching black holes. Figure: Physical Review Letters http://physics.aps.org/articles/v9/17

LIGO Observatory near Livingston, Louisiana. Photo: www.ligo.caltech.edu

Thus, one of the most important tasks that have confronted physicists over the past 100 years. The existence of gravitational waves is predicted by the general theory of relativity (GTR), developed in 1915-1916 by Albert Einstein, the fundamental physical theory that describes the structure and evolution of our world. General relativity, in essence, is a theory of gravity that establishes its connection with the properties of space-time. Massive bodies produce changes in it that are commonly called curvature of space-time. If these bodies move with variable acceleration, then propagating changes in space-time arise, which are called gravitational waves.

The problem with registering them is that gravitational waves are very weak, and their detection from any terrestrial source is almost impossible. Over the years, they have not been detected from most space objects either. Hopes remained only for gravitational waves from major cosmic disasters such as supernova explosions, collisions of neutron stars or black holes. These hopes came true. In this work, gravitational waves were discovered precisely from the merger of two black holes.

To detect gravitational waves, a grandiose project called LIGO (Laser Interferometer Gravitational-Wave Observatory) was proposed in 1992. The technology for it has been developed for almost twenty years. And it was implemented by two of the largest research centers in the United States - the California and Massachusetts Institutes of Technology. The overall scientific team, the LIGO collaboration, includes about 1,000 scientists from 16 countries. Russia is represented in it by Moscow State University and Institute of Applied Physics RAS (Nizhny Novgorod)

LIGO includes observatories in the states of Washington and Louisiana, located at a distance of 3000 km, which is an L-shaped Michelson interferometer with two arms 4 km long. The laser beam, passing through a system of mirrors, is divided into two beams, each of which propagates in its own arm. They are reflected from mirrors and come back. Then these two light waves, traveling along different paths, are added together in the detector. Initially, the system is configured so that the waves cancel each other out and nothing hits the detector. Gravitational waves change the distances between test masses, which simultaneously serve as mirrors of the interferometer, which leads to the fact that the sum of the waves is no longer equal to zero and the signal intensity at the photodetector will be proportional to these changes. This signal is used to register a gravitational wave.

The first, initial, stage of measurements took place in 2002-2010 and did not allow the detection of gravitational waves. The sensitivity of the devices was not enough (shifts up to 4x10 -18 m were tracked). Then it was decided to stop work in 2010 and modernize the equipment, increasing the sensitivity by more than 10 times. The improved equipment, which began work in the second half of 2015, was able to detect a shift of a record 10 -19 m. And already during the test run, scientists were waiting for a discovery; they recorded a gravitational burst from the event, which after a long study was identified as the merger of two black holes with masses at 29 and 36 solar masses.

Simultaneously with Washington, a press conference was held in Moscow. At it, participants in the experiment, representing the Faculty of Physics of Moscow State University, spoke about their contribution to its implementation. V.B. Braginsky’s group participated in the work from the very beginning of the project. Physicists from Moscow State University ensured the assembly of a complex structure, which consists of interferometer mirrors, which simultaneously serve as test masses.

In addition, their tasks included combating extraneous vibrations (noise) that could interfere with the detection of gravitational waves. It was the Moscow State University specialists who proved that the device should be made of fused quartz, which at operating temperatures will make less noise than the sapphire proposed by other researchers. In particular, to reduce thermal noise, it was necessary to ensure that the oscillations of test masses suspended like pendulums did not die out for a very long time. Physicists from Moscow State University have achieved a decay time of 5 years!

The success of the measurements will give rise to a new gravitational-wave astronomy and will allow us to learn a lot of new things about the Universe. Perhaps physicists will be able to unravel some of the mysteries of dark matter and the early stages of the development of the Universe, as well as look into areas where general relativity is violated.

Based on materials from the LIGO collaboration press conference.

February 11th, 2016

Just a few hours ago, news arrived that had been long awaited in the scientific world. A group of scientists from several countries working as part of international project LIGO Scientific Collaboration, claim that with the help of several detector observatories they were able to detect gravitational waves in laboratory conditions.

They are analyzing data coming from two laser interferometer gravitational-wave observatories (Laser Interferometer Gravitational-Wave Observatory - LIGO), located in the states of Louisiana and Washington in the United States.

As stated at the LIGO project press conference, gravitational waves were detected on September 14, 2015, first at one observatory, and then 7 milliseconds later at another.

Based on the analysis of the data obtained, which was carried out by scientists from many countries, including Russia, it was found that the gravitational wave was caused by the collision of two black holes with a mass of 29 and 36 times the mass of the Sun. After that, they merged into one large black hole.

This happened 1.3 billion years ago. The signal came to Earth from the direction of the Magellanic Cloud constellation.

Sergei Popov (astrophysicist at the Sternberg State Astronomical Institute of Moscow State University) explained what gravitational waves are and why it is so important to measure them.

Modern theories of gravity are geometric theories of gravity, more or less everything from the theory of relativity. The geometric properties of space affect the movement of bodies or objects such as a light beam. And vice versa - the distribution of energy (this is the same as mass in space) affects the geometric properties of space. This is very cool, because it’s easy to visualize - this whole elastic plane lined in a box has some physical meaning, although, of course, it’s not all so literal.

Physicists use the word "metric". A metric is something that describes the geometric properties of space. And here we have bodies moving with acceleration. The simplest thing is to rotate the cucumber. It is important that it is not, for example, a ball or a flattened disk. It is easy to imagine that when such a cucumber spins on an elastic plane, ripples will run from it. Imagine that you are standing somewhere, and a cucumber turns one end towards you, then the other. It affects space and time in different ways, a gravitational wave runs.

So, a gravitational wave is a ripple running along the space-time metric.

Beads in space

This is a fundamental property of our basic understanding of how gravity works, and people have been wanting to test it for a hundred years. They want to make sure that there is an effect and that it is visible in the laboratory. This was seen in nature about three decades ago. How should gravitational waves manifest themselves in everyday life?

The easiest way to illustrate this is this: if you throw beads in space so that they lie in a circle, and when a gravitational wave passes perpendicular to their plane, they will begin to turn into an ellipse, compressed first in one direction, then in the other. The point is that the space around them will be disturbed, and they will feel it.

"G" on Earth

People do something like this, only not in space, but on Earth.

Mirrors in the shape of the letter “g” [referring to the American LIGO observatories] hang at a distance of four kilometers from each other.

Running laser beams- this is an interferometer, a well-understood thing. Modern technologies allow you to measure a fantastically small effect. It’s still not that I don’t believe it, I believe it, but I just can’t wrap my head around it - the displacement of mirrors hanging at a distance of four kilometers from each other is less than the size of an atomic nucleus. This is small even compared to the wavelength of this laser. This was the catch: gravity is the weakest interaction, and therefore the displacements are very small.

It took a very long time, people have been trying to do this since the 1970s, they have spent their lives searching for gravitational waves. And now only technical capabilities make it possible to register a gravitational wave in laboratory conditions, that is, it came here and the mirrors shifted.

Direction

Within a year, if all goes well, there will already be three detectors operating in the world. Three detectors are very important, because these things are very bad at determining the direction of the signal. In much the same way as we are bad at determining the direction of a source by ear. “A sound from somewhere on the right” - these detectors sense something like this. But if three people stand at a distance from each other, and one hears a sound from the right, another from the left, and the third from behind, then we can very accurately determine the direction of the sound. The more detectors there are, the more they are scattered around the globe, the more accurately we will be able to determine the direction of the source, and then astronomy will begin.

After all, the ultimate goal is not only to confirm the general theory of relativity, but also to obtain new astronomical knowledge. Just imagine that there is a black hole weighing ten solar masses. And it collides with another black hole weighing ten solar masses. The collision occurs at the speed of light. Energy breakthrough. This is true. There is a fantastic amount of it. And there’s no way... It’s just ripples of space and time. I would say that detecting the merger of two black holes is for a long time will be the strongest evidence yet that black holes are just about the black holes we think they are.

Let's go through the issues and phenomena that it could reveal.

Do black holes really exist?

The signal expected from the LIGO announcement may have been produced by two merging black holes. Such events are the most energetic ones known; the strength of the gravitational waves emitted by them can briefly outshine all the stars in the observable universe combined. Merging black holes are also quite easy to interpret from their very pure gravitational waves.

A black hole merger occurs when two black holes spiral around each other, emitting energy in the form of gravitational waves. These waves have a characteristic sound (chirp) that can be used to measure the mass of these two objects. After this, black holes usually merge.

“Imagine two soap bubbles that come so close that they form one bubble. The larger bubble is deformed," says Tybalt Damour, a gravitational theorist at the Institute for Advanced scientific research near Paris. The final black hole will be perfectly spherical, but must first emit predictable types of gravitational waves.

One of the most important scientific consequences of detecting a black hole merger will be the confirmation of the existence of black holes - at least perfectly round objects consisting of pure, empty, curved space-time, as predicted by general relativity. Another consequence is that the merger is proceeding as scientists predicted. Astronomers have a lot of indirect evidence of this phenomenon, but so far these have been observations of stars and superheated gas in the orbit of black holes, and not the black holes themselves.

“The scientific community, including myself, doesn’t like black holes. We take them for granted, says France Pretorius, a general relativity simulation specialist at Princeton University in New Jersey. “But when we think about how amazing this prediction is, we need some truly amazing proof.”

Do gravitational waves travel at the speed of light?

When scientists start comparing LIGO observations with those from other telescopes, the first thing they check is whether the signal arrived at the same time. Physicists believe that gravity is transmitted by graviton particles, the gravitational analogue of photons. If, like photons, these particles have no mass, then gravitational waves will travel at the speed of light, matching the prediction of the speed of gravitational waves in classical relativity. (Their speed may be affected by the accelerating expansion of the Universe, but this should be evident at distances significantly greater than those covered by LIGO).

It is quite possible, however, that gravitons have a small mass, which means that gravitational waves will move at a speed less than light. So, for example, if LIGO and Virgo detect gravitational waves and find that the waves arrived on Earth after cosmic event-related gamma rays, this could have life-changing consequences for fundamental physics.

Is space-time made of cosmic strings?

An even stranger discovery could occur if bursts of gravitational waves are found emanating from “cosmic strings.” These hypothetical defects in the curvature of spacetime, which may or may not be related to string theories, should be infinitely thin, but stretched to cosmic distances. Scientists predict that cosmic strings, if they exist, may accidentally bend; if the string were to bend, it would cause a gravitational surge that detectors like LIGO or Virgo could measure.

Can neutron stars be lumpy?

Neutron stars are the remains of large stars that collapsed under their own weight and became so dense that electrons and protons began to fuse into neutrons. Scientists have little understanding of the physics of neutron holes, but gravitational waves could tell us a lot about them. For example, the intense gravity on their surface causes neutron stars to become almost perfectly spherical. But some scientists have suggested that there may also be "mountains" - a few millimeters high - that make these dense objects, no more than 10 kilometers in diameter, slightly asymmetrical. Neutron stars typically spin very quickly, so the asymmetric distribution of mass will warp spacetime and produce a persistent gravitational wave signal in the shape of a sine wave, slowing the star's rotation and emitting energy.

Pairs of neutron stars that orbit each other also produce a constant signal. Like black holes, these stars move in a spiral and eventually merge with a characteristic sound. But its specificity differs from the specificity of the sound of black holes.

Why do stars explode?

Black holes and neutron stars form when massive stars stop shining and collapse in on themselves. Astrophysicists think this process underlies all common types of Type II supernova explosions. Simulations of such supernovae have not yet shown what causes them to ignite, but listening to the gravitational wave bursts emitted by a real supernova is thought to provide an answer. Depending on what the burst waves look like, how loud they are, how often they occur, and how they correlate with supernovae that electromagnetic telescopes are tracking, this data could help rule out a bunch of existing models.

How fast is the Universe expanding?

The expansion of the Universe means that distant objects that move away from our galaxy appear redder than they really are because the light they emit is stretched as they move. Cosmologists estimate the rate of expansion of the Universe by comparing the redshift of galaxies with how far away they are from us. But this distance is usually estimated from the brightness of Type Ia supernovae, and this technique leaves a lot of uncertainties.

If several gravitational wave detectors around the world detect signals from the merger of the same neutron stars, together they can absolutely accurately estimate the volume of the signal, and therefore the distance at which the merger occurred. They will also be able to estimate the direction, and with it, identify the galaxy in which the event occurred. By comparing the redshift of this galaxy with the distance to the merging stars, it is possible to obtain an independent rate of cosmic expansion, perhaps more accurate than current methods allow.

sources

http://www.bbc.com/russian/science/2016/02/160211_gravitational_waves

http://cont.ws/post/199519

Here we somehow found out, but what is and. Look what it looks like The original article is on the website InfoGlaz.rf Link to the article from which this copy was made -

Let us recall that the other day LIGO scientists announced a major breakthrough in the field of physics, astrophysics and our study of the Universe: the discovery of gravitational waves, predicted by Albert Einstein 100 years ago. Gizmodo caught up with Dr. Amber Staver of the Livingston Observatory in Louisiana, a LIGO collaboration, to ask more about what this means for physics. We understand that in just a few articles it will be difficult to achieve a global understanding of a new way of understanding our world, but we will try.

A huge amount of work has been done to detect a single gravitational wave so far, and it was a major breakthrough. It looks like it's opening up a ton of new possibilities for astronomy - but is this first detection just "simple" proof that the detection is possible in itself, or can you already learn further from it? scientific achievements? What do you hope to get out of it in the future? Will there be simpler methods for detecting these waves in the future?

This is really a first discovery, a breakthrough, but the goal has always been to use gravitational waves to do new astronomy. Instead of searching the Universe for visible light, we can now sense subtle changes in gravity that are caused by the biggest, strongest, and (in my opinion) most interesting things in the Universe - including some that we could never know about with with the help of light.

We were able to apply this new type of astronomy to the first detection waves. Using what we already know about GTR (general relativity), we were able to predict what gravitational waves from objects like black holes or neutron stars are like. The signal we found matches that predicted for a pair of black holes, one 36 and the other 29 times as massive as the Sun, swirling as they approach each other. Finally, they merge into one black hole. So this is not only the first detection of gravitational waves, but also the first direct observation of black holes, because they cannot be observed using light (only by the matter that orbits around them).

Why are you sure that extraneous effects (like vibration) do not affect the results?

In LIGO, we record much more data related to our environment and equipment than data that might contain a gravitational wave signal. The reason for this is that we want to be as confident as possible that we are not being fooled by extraneous effects or misled into detecting a gravitational wave. If we sense abnormal soil when a gravitational wave signal is detected, we will most likely reject this candidate.

Video: Gravitational waves in a nutshell

Another measure we take to make sure we don't see something random is to have both LIGO detectors see the same signal within the amount of time it takes for the gravitational wave to travel between the two objects. The maximum time for such a trip is approximately 10 milliseconds. To be sure of possible detection, we must see signals of the same shape, at almost the same time, and the data we collect about our environment must be free of anomalies.

There are many other tests that a candidate takes, but these are the main ones.

Does it exist practical way generate gravitational waves that can be detected using such devices? Will we be able to build a gravitational radio or laser?

You are proposing what Heinrich Hertz did in the late 1880s to detect electromagnetic waves in the form of radio waves. But gravity is the weakest of the fundamental forces that hold the Universe together. For this reason, the movement of mass in a laboratory or other facility to create gravitational waves will be too weak to be detected even by a detector such as LIGO. To create strong enough waves, we would have to spin the dumbbell so fast that it would rip through any known material. But there are many large volumes of mass in the Universe that move extremely quickly, so we are building detectors that will search for them.

Will this confirmation change our future? Will we be able to use the power of these waves to explore outer space? Will it be possible to communicate using these waves?

Because of the amount of mass that must move at extreme speeds to produce gravitational waves that detectors like LIGO can detect, the only known mechanism These are pairs of neutron stars or black holes rotating before merging (there may be other sources). The chances that it is some advanced civilization manipulating matter are extremely low. Personally, I don't think it would be great to discover a civilization capable of using gravitational waves as a means of communication, since they could easily kill us off.

Are gravitational waves coherent? Is it possible to make them coherent? Is it possible to focus them? What will happen to massive object, which is affected by a focused gravitational beam? Can this effect be used to improve particle accelerators?

Some types of gravitational waves can be coherent. Let's imagine a neutron star that is almost perfectly spherical. If it rotates quickly, small deformations of less than an inch will produce gravitational waves of a certain frequency, which will make them coherent. But focusing gravitational waves is very difficult because the Universe is transparent to them; gravitational waves travel through matter and come out unchanged. You need to change the path of at least some of the gravitational waves to focus them. Perhaps an exotic form of gravitational lensing could at least partially focus gravitational waves, but it would be difficult, if not impossible, to harness them. If they can be focused, they will still be so weak that I can't imagine any practical use for them. But they've also talked about lasers, which are essentially just focused coherent light, so who knows.

What is the speed of a gravitational wave? Does it have mass? If not, can it travel faster than the speed of light?

Gravitational waves are believed to travel at the speed of light. This is the speed limited by general relativity. But experiments like LIGO should test this. Perhaps they move a little slower than the speed of light. If so, then the theoretical particle associated with gravity, the graviton, will have mass. Since gravity itself acts between masses, this will add complexity to the theory. But not impossibility. We use Occam's razor: the simplest explanation is usually the most correct.

How far do you need to be from a black hole merger to be able to talk about them?

In the case of our binary black holes, which we detected from gravitational waves, they produced a maximum change in the length of our 4-kilometer arms of 1 x 10 -18 meters (that's 1/1000 the diameter of a proton). We also believe that these black holes are 1.3 billion light years from Earth.

Now suppose that we are two meters tall and we are floating at the distance of the Earth to the Sun from the black hole. I think you would experience alternating flattening and stretching by about 165 nanometers (your height changes by higher value during the day). This can be survived.

In a new way to hear the cosmos, what are scientists most interested in?

The potential is not fully known, in the sense that there may be more places than we thought. The more we learn about the Universe, the better we will be able to answer its questions using gravitational waves. For example, these:

• What causes gamma-ray bursts?
• How does a substance behave in extreme conditions collapsing star?
• What were the first moments after the Big Bang?
• How does matter behave in neutron stars?

But I'm more interested in what unexpected things can be discovered using gravitational waves. Every time people observed the Universe in a new way, we discovered many unexpected things that turned our understanding of the Universe upside down. I want to find these gravitational waves and discover something that we had no idea about before.

Will this help us make a real warp drive?

Since gravitational waves interact weakly with matter, they can hardly be used to move that matter. But even if you could, a gravitational wave only travels at the speed of light. They are not suitable for warp drive. It would be cool though.

What about anti-gravity devices?

To create an anti-gravity device, we need to turn the force of attraction into a force of repulsion. And although a gravitational wave propagates changes in gravity, the change will never be repulsive (or negative).

Gravity always attracts because negative mass doesn't seem to exist. After all, there is positive and negative charge, a north and south magnetic pole, but only positive mass. Why? If negative mass existed, the ball of matter would fall up instead of down. It would be repelled by the positive mass of the Earth.

What does this mean for the ability to time travel and teleportation? Can we find a practical application for this phenomenon, other than studying our Universe?

Now The best way time travel (and only to the future) means traveling at near-light speed (remember the twin paradox in General Relativity) or going to an area with increased gravity (this kind of time travel was demonstrated in Interstellar). Because a gravitational wave propagates changes in gravity, it will produce very small fluctuations in the speed of time, but since gravitational waves are inherently weak, so are the time fluctuations. And while I don't think this can be applied to time travel (or teleportation), never say never (I bet it took your breath away).

Will there come a day when we stop validating Einstein and start looking for strange things again?

Certainly! Since gravity is the weakest of the forces, it is also difficult to experiment with. Until now, every time scientists tested general relativity, they received exactly predicted results. Even the detection of gravitational waves in Once again confirmed Einstein's theory. But I believe that when we start testing the smallest details of the theory (maybe with gravitational waves, maybe with something else), we will find “funny” things, like the experimental result not exactly matching the prediction. This will not mean that GTR is erroneous, only the need to clarify its details.

Video: How did gravitational waves blow up the Internet?

Every time we answer one question about nature, new ones arise. Eventually we will have questions that are cooler than the answers that general relativity can provide.

Can you explain how this discovery might relate to or affect unified field theory? Are we closer to confirming it or debunking it?

Now the results of our discovery are mainly devoted to testing and confirming general relativity. Unified field theory seeks to create a theory that explains the physics of the very small (quantum mechanics) and the very large (general relativity). Now these two theories can be generalized to explain the scale of the world in which we live, but no more. Because our discovery focuses on the physics of the very large, on its own it will do little to advance us toward a unified theory. But that's not the question. The field of gravitational wave physics has just been born. As we learn more, we will certainly expand our results into the realm of unified theory. But before you run, you need to walk.

Now that we're listening to gravitational waves, what do scientists have to hear to literally blow a brick? 1) Unnatural patterns/structures? 2) Sources of gravitational waves from regions that we thought were empty? 3) Rick Astley - Never gonna give you up?

When I read your question, I immediately remembered the scene from Contact in which the radio telescope picks up patterns prime numbers. This is unlikely to be found in nature (as far as we know). So your option with an unnatural pattern or structure would be most likely.

I don't think we will ever be sure that there is a void in a certain region of space. In the end, the black hole system we discovered was isolated and no light was coming from the region, but we still detected gravitational waves there.

Regarding music... I specialize in separating gravitational wave signals from the static noise we constantly measure in the background environment. If I found music in a gravitational wave, especially music that I had heard before, it would be a hoax. But music that has never been heard on Earth... It would be like simple cases from Contact.

Since the experiment detects waves by changing the distance between two objects, is the amplitude of one direction greater than the other? Otherwise, wouldn't the data being read mean that the Universe is changing in size? And if so, does this confirm the expansion or something unexpected?

We need to see many gravitational waves coming from many different directions in the Universe before we can answer this question. In astronomy, this creates a population model. How many different types of things are there? This main question. Once we have a lot of observations and start to see unexpected patterns, for example that gravitational waves of a certain type come from a certain part of the Universe and nowhere else, this will be an extremely interesting result. Some patterns could confirm expansion (of which we are very confident) or other phenomena that we are not yet aware of. But first we need to see a lot more gravitational waves.

It is completely incomprehensible to me how scientists determined that the waves they measured belong to two supermassive black holes. How can one determine the source of the waves with such accuracy?

Data analysis methods use a catalog of predicted gravitational wave signals to compare with our data. If there is a strong correlation with one of these predictions, or patterns, then we not only know that it is a gravitational wave, but we also know what system produced it.

Every single way a gravitational wave is created, whether it's through black holes merging, stars spinning, or stars dying, all waves have different shapes. When we detect a gravitational wave, we use these shapes, as predicted by general relativity, to determine their cause.

How do we know that these waves came from the collision of two black holes and not some other event? Is it possible to predict where or when such an event occurred with any degree of accuracy?

Once we know which system produced the gravitational wave, we can predict how strong the gravitational wave was close to where it originated. By measuring its strength as it reaches Earth and comparing our measurements to the predicted strength of the source, we can calculate how far away the source is. Since gravitational waves travel at the speed of light, we can also calculate how long it took the gravitational waves to travel towards Earth.

In the case of the black hole system we discovered, we measured the maximum change in the length of the LIGO arms per 1/1000th of the proton diameter. This system is located 1.3 billion light years away. The gravitational wave, discovered in September and announced recently, has been moving towards us for 1.3 billion years. This happened before animal life formed on Earth, but after the emergence of multicellular organisms.

At the time of the announcement, it was stated that other detectors would look for waves with longer periods - some of them even cosmic. What can you tell us about these large detectors?

There is indeed a space detector in development. It's called LISA (Laser Interferometer Space Antenna). Since it will be in space, it will be quite sensitive to low-frequency gravitational waves, unlike earth-based detectors, due to the natural vibrations of the Earth. It will be difficult because the satellites will have to be placed further from the Earth than humans have ever been. If something goes wrong, we won't be able to send astronauts out for repairs like we did with Hubble in the 1990s. To test the necessary technologies, the LISA Pathfinder mission was launched in December. So far, she has completed all her tasks, but the mission is far from over.

Is it possible to convert gravitational waves into sound waves? And if so, what will they look like?

Can. Of course, you won't just hear a gravitational wave. But if you take the signal and pass it through the speakers, you can hear it.

What should we do with this information? Do other astronomical objects with significant mass emit these waves? Can waves be used to find planets or simple black holes?

When searching for gravitational values, it's not just mass that matters. Also the acceleration that is inherent to an object. The black holes we discovered were spinning around each other at 60% the speed of light when they merged. That's why we were able to detect them during the merger. But now there are no more gravitational waves coming from them, since they have merged into one inactive mass.

So anything that has a lot of mass and moves very quickly creates gravitational waves that can be detected.

Exoplanets are unlikely to have sufficient mass or acceleration to produce detectable gravitational waves. (I'm not saying they don't create them at all, only that they won't be strong enough or at a different frequency). Even if the exoplanet were massive enough to produce the necessary waves, the acceleration would tear it apart. Don't forget that the most massive planets tend to be gas giants.

How true is the analogy of waves in water? Can we ride these waves? Do gravitational “peaks” exist, like the already known “wells”?

Since gravitational waves can move through matter, there is no way to ride them or harness them for propulsion. So no gravitational wave surfing.

"Peaks" and "wells" are great. Gravity always attracts because there is no negative mass. We don't know why, but it has never been observed in the laboratory or in the universe. Therefore, gravity is usually represented as a “well.” The mass that moves along this “well” will fall deeper; This is how attraction works. If you have a negative mass, then you will get repulsion, and with it a “peak”. A mass that moves at the “peak” will bend away from it. So “wells” exist, but “peaks” do not.

The analogy with water is fine, as long as we talk about the fact that the strength of the wave decreases with the distance traveled from the source. The water wave will become smaller and smaller, and the gravity wave will become weaker and weaker.

How will this discovery affect our description of the inflationary period of the Big Bang?

On this moment this discovery has so far had virtually no effect on inflation. To make statements like this, one must observe the relic gravitational waves of the Big Bang. The BICEP2 project thought it had indirectly observed these gravitational waves, but it turned out that cosmic dust was to blame. If he gets the right data, it will also confirm the existence of a short period of inflation shortly after the Big Bang.

LIGO will be able to see these gravitational waves directly (this will also be the weakest type of gravitational waves we hope to detect). If we see them, we will be able to look deep into the past of the Universe, as we have not looked before, and judge inflation from the data obtained.