Gravitational wave
General relativity |
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Gravitational waves are waves of the intensity of
Gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation.[7] Newton's law of universal gravitation, part of classical mechanics, does not provide for their existence, since that law is predicated on the assumption that physical interactions propagate instantaneously (at infinite speed) – showing one of the ways the methods of Newtonian physics are unable to explain phenomena associated with relativity.
The first indirect evidence for the existence of gravitational waves came in 1974 from the observed orbital decay of the
The first
In gravitational-wave astronomy, observations of gravitational waves are used to infer data about the sources of gravitational waves. Sources that can be studied this way include binary star systems composed of white dwarfs, neutron stars,[8][9] and black holes; events such as supernovae; and the formation of the early universe shortly after the Big Bang.
Introduction
In Einstein's general theory of relativity, gravity is treated as a phenomenon resulting from the curvature of spacetime. This curvature is caused by the presence of mass. Generally, the more mass that is contained within a given volume of space, the greater the curvature of spacetime will be at the boundary of its volume.[10] As objects with mass move around in spacetime, the curvature changes to reflect the changed locations of those objects. In certain circumstances, accelerating objects generate changes in this curvature which propagate outwards at the speed of light in a wave-like manner. These propagating phenomena are known as gravitational waves.
As a gravitational wave passes an observer, that observer will find spacetime distorted by the effects of
Inspiraling binary neutron stars are predicted to be a powerful source of gravitational waves as they coalesce, due to the very large acceleration of their masses as they orbit close to one another. However, due to the astronomical distances to these sources, the effects when measured on Earth are predicted to be very small, having strains of less than 1 part in 1020.
Where General Relativity is accepted, gravitational waves as detected are attributed to ripples in spacetime; otherwise the gravitational waves can be thought of simply as a product of the orbit of binary systems. (A binary orbit causes the binary system's geometry to change through 180 degrees and also causes the distance between each body of the binary system and the observer to change through 180 degrees causing a gravitational wave frequency of two times the orbital frequency).
Scientists continue to demonstrate the existence of these waves with continuously upgraded, highly-sensitive detectors used in joint observation runs. The most sensitive detector accomplished the task possessing a sensitivity measurement of about one part in 5×1022 (as of 2012[update]) provided by the LIGO and VIRGO observatories.[12] In 2019, the Japanese detector KAGRA was completed and made its first joint detection with LIGO and VIRGO in 2021.[13] A space based observatory, the Laser Interferometer Space Antenna, is currently under development by ESA. Another European ground based detector, the Einstein Telescope, is also being developed.
Gravitational waves can penetrate regions of space that electromagnetic waves cannot. They allow the observation of the merger of black holes and possibly other exotic objects in the distant Universe. Such systems cannot be observed with more traditional means such as
In particular, gravitational waves could be of interest to cosmologists as they offer a possible way of observing the very early Universe. This is not possible with conventional astronomy, since before recombination the Universe was opaque to electromagnetic radiation.[14] Precise measurements of gravitational waves will also allow scientists to test more thoroughly the general theory of relativity.
In principle, gravitational waves can exist at any frequency. Very low frequency waves are detected using pulsar timing arrays. Astronomers monitor the timing of approximately 100 pulsars spread widely across our galaxy over the course of years. Detectable changes in the arrival time of their signals can result from passing gravitational waves generated by merging supermassive black holes with wavelengths measured in lightyears. These timing changes can be used to locate the source of the waves.[citation needed]
Using this technique, astronomers have discovered the 'hum' of various SMBH mergers occurring in the universe. Stephen Hawking and Werner Israel list different frequency bands for gravitational waves that could plausibly be detected, ranging from 10−7 Hz up to 1011 Hz.[15]
Speed of gravity
The speed of gravitational waves in the
Thus, the speed of "light" is also the speed of gravitational waves, and further the speed of any massless particle. Such particles include the gluon (carrier of the strong force), the photons that make up light (hence carrier of electromagnetic force), and the hypothetical gravitons (which are the presumptive field particles associated with gravity; however, an understanding of the graviton, if any exist, requires an as-yet unavailable theory of quantum gravity).
In August 2017, the LIGO and Virgo detectors received gravitational wave signals within 2 seconds of gamma ray satellites and optical telescopes seeing signals from the same direction. This confirmed that the speed of gravitational waves was the same as the speed of light.[18]
History
The possibility of gravitational waves and that those might travel at the speed of light was discussed in 1893 by
In 1915 Einstein published his general theory of relativity, a complete relativistic theory of gravitation. He conjectured, like Poincare, that the equation would produce gravitational waves, but, as he mentions in a letter to Schwarzschild in February 1916,[25] these could not be similar to electromagnetic waves. Electromagnetic waves are produced by dipole motion, requiring both a positive and a negative charge; gravitation has no equivalent to negative charge. Einstein continued to work through the complexity of the equations of general relativity to find an alternative wave model. The result was published in June 1916,[4] and there he came to the conclusion that the gravitational wave must propagate with the speed of light, and there must, in fact, be three types of gravitational waves dubbed longitudinal–longitudinal, transverse–longitudinal, and transverse–transverse by Hermann Weyl.[25]
However, the nature of Einstein's approximations led many (including Einstein himself) to doubt the result. In 1922, Arthur Eddington showed that two of Einstein's types of waves were artifacts of the coordinate system he used, and could be made to propagate at any speed by choosing appropriate coordinates, leading Eddington to jest that they "propagate at the speed of thought".[26]: 72 This also cast doubt on the physicality of the third (transverse–transverse) type that Eddington showed always propagate at the speed of light regardless of coordinate system. In 1936, Einstein and Nathan Rosen submitted a paper to Physical Review in which they claimed gravitational waves could not exist in the full general theory of relativity because any such solution of the field equations would have a singularity. The journal sent their manuscript to be reviewed by Howard P. Robertson, who anonymously reported that the singularities in question were simply the harmless coordinate singularities of the employed cylindrical coordinates. Einstein, who was unfamiliar with the concept of peer review, angrily withdrew the manuscript, never to publish in Physical Review again. Nonetheless, his assistant Leopold Infeld, who had been in contact with Robertson, convinced Einstein that the criticism was correct, and the paper was rewritten with the opposite conclusion and published elsewhere.[25][26]: 79ff In 1956, Felix Pirani remedied the confusion caused by the use of various coordinate systems by rephrasing the gravitational waves in terms of the manifestly observable Riemann curvature tensor.[27]
At the time, Pirani's work was overshadowed by the community's focus on a different question: whether gravitational waves could transmit energy. This matter was settled by a thought experiment proposed by Richard Feynman during the first "GR" conference at Chapel Hill in 1957. In short, his argument known as the "sticky bead argument" notes that if one takes a rod with beads then the effect of a passing gravitational wave would be to move the beads along the rod; friction would then produce heat, implying that the passing wave had done work. Shortly after, Hermann Bondi published a detailed version of the "sticky bead argument".[25] This later led to a series of articles (1959 to 1989) by Bondi and Pirani that established the existence of plane wave solutions for gravitational waves.[28]
Paul Dirac further postulated the existence of gravitational waves, declaring them to have "physical significance" in his 1959 lecture at the Lindau Meetings.[29] Further, it was Dirac who predicted gravitational waves with a well defined energy density in 1964.[30]
After the Chapel Hill conference, Joseph Weber started designing and building the first gravitational wave detectors now known as Weber bars. In 1969, Weber claimed to have detected the first gravitational waves, and by 1970 he was "detecting" signals regularly from the Galactic Center; however, the frequency of detection soon raised doubts on the validity of his observations as the implied rate of energy loss of the Milky Way would drain our galaxy of energy on a timescale much shorter than its inferred age. These doubts were strengthened when, by the mid-1970s, repeated experiments from other groups building their own Weber bars across the globe failed to find any signals, and by the late 1970s consensus was that Weber's results were spurious.[25]
In the same period, the first indirect evidence of gravitational waves was discovered. In 1974,
This indirect detection of gravitational waves motivated further searches, despite Weber's discredited result. Some groups continued to improve Weber's original concept, while others pursued the detection of gravitational waves using laser interferometers. The idea of using a laser interferometer for this seems to have been floated independently by various people, including M. E. Gertsenshtein and V. I. Pustovoit in 1962,[34] and Vladimir B. Braginskiĭ in 1966. The first prototypes were developed in the 1970s by Robert L. Forward and Rainer Weiss.[35][36] In the decades that followed, ever more sensitive instruments were constructed, culminating in the construction of GEO600, LIGO, and Virgo.[25]
After years of producing null results, improved detectors became operational in 2015. On 11 February 2016, the
A year earlier, the BICEP2 collaboration claimed that they had detected the imprint of gravitational waves in the cosmic microwave background. However, they were later forced to retract this result.[19][20][43][44]
In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry Barish for their role in the detection of gravitational waves.[45][46][47]
In 2023, NANOGrav, EPTA, PPTA, and IPTA announced that they found evidence of a universal gravitational wave background.[48] North American Nanohertz Observatory for Gravitational Waves states, that they were created over cosmological time scales by supermassive black holes, identifying the distinctive Hellings-Downs curve in 15 years of radio observations of 25 pulsars.[49] Similar results are published by European Pulsar Timing Array, who claimed a -significance. They expect that a -significance will be achieved by 2025 by combining the measurements of several collaborations.[50][51]
Effects of passing
Gravitational waves are constantly passing
The effects of a passing gravitational wave, in an extremely exaggerated form, can be visualized by imagining a perfectly flat region of spacetime with a group of motionless test particles lying in a plane, e.g., the surface of a computer screen. As a gravitational wave passes through the particles along a line perpendicular to the plane of the particles, i.e., following the observer's line of vision into the screen, the particles will follow the distortion in spacetime, oscillating in a "cruciform" manner, as shown in the animations. The area enclosed by the test particles does not change and there is no motion along the direction of propagation.[citation needed]
The oscillations depicted in the animation are exaggerated for the purpose of discussion – in reality a gravitational wave has a very small amplitude (as formulated in linearized gravity). However, they help illustrate the kind of oscillations associated with gravitational waves as produced by a pair of masses in a circular orbit. In this case the amplitude of the gravitational wave is constant, but its plane of polarization changes or rotates at twice the orbital rate, so the time-varying gravitational wave size, or 'periodic spacetime strain', exhibits a variation as shown in the animation.[53] If the orbit of the masses is elliptical then the gravitational wave's amplitude also varies with time according to Einstein's quadrupole formula.[4]
As with other waves, there are a number of characteristics used to describe a gravitational wave:
- Amplitude: Usually denoted h, this is the size of the wave – the fraction of stretching or squeezing in the animation. The amplitude shown here is roughly h = 0.5 (or 50%). Gravitational waves passing through the Earth are many sextilliontimes weaker than this – h ≈ 10−20.
- Frequency: Usually denoted f, this is the frequency with which the wave oscillates (1 divided by the amount of time between two successive maximum stretches or squeezes)
- Wavelength: Usually denoted λ, this is the distance along the wave between points of maximum stretch or squeeze.
- Speed: This is the speed at which a point on the wave (for example, a point of maximum stretch or squeeze) travels. For gravitational waves with small amplitudes, this wave speed is equal to the speed of light (c).
The speed, wavelength, and frequency of a gravitational wave are related by the equation c = λf, just like the equation for a light wave. For example, the animations shown here oscillate roughly once every two seconds. This would correspond to a frequency of 0.5 Hz, and a wavelength of about 600 000 km, or 47 times the diameter of the Earth.
In the above example, it is assumed that the wave is linearly polarized with a "plus" polarization, written h+. Polarization of a gravitational wave is just like polarization of a light wave except that the polarizations of a gravitational wave are 45 degrees apart, as opposed to 90 degrees.[54] In particular, in a "cross"-polarized gravitational wave, h×, the effect on the test particles would be basically the same, but rotated by 45 degrees, as shown in the second animation. Just as with light polarization, the polarizations of gravitational waves may also be expressed in terms of circularly polarized waves. Gravitational waves are polarized because of the nature of their source.
Sources
In general terms, gravitational waves are radiated by objects whose motion involves acceleration and its change, provided that the motion is not perfectly spherically
Some more detailed examples:
- Two objects orbiting each other, as a planet would orbit the Sun, will radiate.
- A spinning non-axisymmetric planetoid – say with a large bump or dimple on the equator – will radiate.
- A supernova will radiate except in the unlikely event that the explosion is perfectly symmetric.
- An isolated non-spinning solid object moving at a constant velocity will not radiate. This can be regarded as a consequence of the principle of conservation of linear momentum.
- A spinning disk will not radiate. This can be regarded as a consequence of the principle of conservation of angular momentum. However, it will show gravitomagneticeffects.
- A spherically pulsating spherical star (non-zero monopole moment or mass, but zero quadrupole moment) will not radiate, in agreement with Birkhoff's theorem.
More technically, the second time derivative of the quadrupole moment (or the l-th time derivative of the l-th multipole moment) of an isolated system's stress–energy tensor must be non-zero in order for it to emit gravitational radiation. This is analogous to the changing dipole moment of charge or current that is necessary for the emission of electromagnetic radiation.
Binaries
Gravitational waves carry energy away from their sources and, in the case of orbiting bodies, this is associated with an in-spiral or decrease in orbit.[56][57] Imagine for example a simple system of two masses – such as the Earth–Sun system – moving slowly compared to the speed of light in circular orbits. Assume that these two masses orbit each other in a circular orbit in the x–y plane. To a good approximation, the masses follow simple Keplerian orbits. However, such an orbit represents a changing quadrupole moment. That is, the system will give off gravitational waves.
In theory, the loss of energy through gravitational radiation could eventually drop the Earth into the
More generally, the rate of orbital decay can be approximated by[59]
where r is the separation between the bodies, t time, G the gravitational constant, c the speed of light, and m1 and m2 the masses of the bodies. This leads to an expected time to merger of [59]
Compact binaries
When the orbit of a neutron star binary has decayed to 1.89×106 m (1890 km), its remaining lifetime is about 130,000 seconds or 36 hours. The orbital frequency will vary from 1 orbit per second at the start, to 918 orbits per second when the orbit has shrunk to 20 km at merger. The majority of gravitational radiation emitted will be at twice the orbital frequency. Just before merger, the inspiral could be observed by LIGO if such a binary were close enough. LIGO has only a few minutes to observe this merger out of a total orbital lifetime that may have been billions of years. In August 2017, LIGO and Virgo observed the first binary neutron star inspiral in
Black hole binaries
Black hole binaries emit gravitational waves during their in-spiral,
Supernova
A supernova is a
Spinning neutron stars
As noted above, a mass distribution will emit gravitational radiation only when there is spherically asymmetric motion among the masses. A spinning neutron star will generally emit no gravitational radiation because neutron stars are highly dense objects with a strong gravitational field that keeps them almost perfectly spherical. In some cases, however, there might be slight deformities on the surface called "mountains", which are bumps extending no more than 10 centimeters (4 inches) above the surface,[66] that make the spinning spherically asymmetric. This gives the star a quadrupole moment that changes with time, and it will emit gravitational waves until the deformities are smoothed out.
Inflation
Many models of the Universe suggest that there was an inflationary epoch in the early history of the Universe when space expanded by a large factor in a very short amount of time. If this expansion was not symmetric in all directions, it may have emitted gravitational radiation detectable today as a gravitational wave background. This background signal is too weak for any currently operational gravitational wave detector to observe, and it is thought it may be decades before such an observation can be made.
Properties and behaviour
Energy, momentum, and angular momentum
Water waves, sound waves, and electromagnetic waves are able to carry energy, momentum, and angular momentum and by doing so they carry those away from the source. Gravitational waves perform the same function. Thus, for example, a binary system loses angular momentum as the two orbiting objects spiral towards each other—the angular momentum is radiated away by gravitational waves.
The waves can also carry off linear momentum, a possibility that has some interesting implications for
Redshifting
Like
Quantum gravity, wave-particle aspects, and graviton
In the framework of
If such a particle exists, it is expected to be massless (because the gravitational force appears to have unlimited range) and must be a spin-2 boson. It can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field must couple to (interact with) the stress–energy tensor in the same way that the gravitational field does; therefore if a massless spin-2 particle were ever discovered, it would be likely to be the graviton without further distinction from other massless spin-2 particles.[71] Such a discovery would unite quantum theory with gravity.[72]
Significance for study of the early universe
Due to the weakness of the coupling of gravity to matter, gravitational waves experience very little absorption or scattering, even as they travel over astronomical distances. In particular, gravitational waves are expected to be unaffected by the opacity of the very early universe. In these early phases, space had not yet become "transparent", so observations based upon light, radio waves, and other electromagnetic radiation that far back into time are limited or unavailable. Therefore, gravitational waves are expected in principle to have the potential to provide a wealth of observational data about the very early universe.[73]
Determining direction of travel
The difficulty in directly detecting gravitational waves means it is also difficult for a single detector to identify by itself the direction of a source. Therefore, multiple detectors are used, both to distinguish signals from other "noise" by confirming the signal is not of earthly origin, and also to determine direction by means of triangulation. This technique uses the fact that the waves travel at the speed of light and will reach different detectors at different times depending on their source direction. Although the differences in arrival time may be just a few milliseconds, this is sufficient to identify the direction of the origin of the wave with considerable precision.
Only in the case of GW170814 were three detectors operating at the time of the event, therefore, the direction is precisely defined. The detection by all three instruments led to a very accurate estimate of the position of the source, with a 90% credible region of just 60 deg2, a factor 20 more accurate than before.[74]
Gravitational wave astronomy
During the past century,
Gravitational waves have two important and unique properties. First, there is no need for any type of matter to be present nearby in order for the waves to be generated by a binary system of uncharged black holes, which would emit no electromagnetic radiation. Second, gravitational waves can pass through any intervening matter without being scattered significantly. Whereas light from distant stars may be blocked out by
The sources of gravitational waves described above are in the low-frequency end of the gravitational-wave spectrum (10−7 to 105 Hz). An astrophysical source at the high-frequency end of the gravitational-wave spectrum (above 105 Hz and probably 1010 Hz) generates[clarification needed] relic gravitational waves that are theorized to be faint imprints of the Big Bang like the cosmic microwave background.[77] At these high frequencies it is potentially possible that the sources may be "man made"[15] that is, gravitational waves generated and detected in the laboratory.[78][79]
A supermassive black hole, created from the merger of the black holes at the center of two merging galaxies detected by the Hubble Space Telescope, is theorized to have been ejected from the merger center by gravitational waves.[80][81]
Detection
Indirect detection
Although the waves from the Earth–Sun system are minuscule, astronomers can point to other sources for which the radiation should be substantial. One important example is the
The information about the orbit can be used to predict how much energy (and angular momentum) would be radiated in the form of gravitational waves. As the binary system loses energy, the stars gradually draw closer to each other, and the orbital period decreases. The resulting trajectory of each star is an inspiral, a spiral with decreasing radius. General relativity precisely describes these trajectories; in particular, the energy radiated in gravitational waves determines the rate of decrease in the period, defined as the time interval between successive periastrons (points of closest approach of the two stars). For the Hulse–Taylor pulsar, the predicted current change in radius is about 3 mm per orbit, and the change in the 7.75 hr period is about 2 seconds per year. Following a preliminary observation showing an orbital energy loss consistent with gravitational waves,[32] careful timing observations by Taylor and Joel Weisberg dramatically confirmed the predicted period decrease to within 10%.[84] With the improved statistics of more than 30 years of timing data since the pulsar's discovery, the observed change in the orbital period currently matches the prediction from gravitational radiation assumed by general relativity to within 0.2 percent.[85] In 1993, spurred in part by this indirect detection of gravitational waves, the Nobel Committee awarded the Nobel Prize in Physics to Hulse and Taylor for "the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation."[86] The lifetime of this binary system, from the present to merger is estimated to be a few hundred million years.[87]
Inspirals are very important sources of gravitational waves. Any time two compact objects (white dwarfs, neutron stars, or black holes) are in close orbits, they send out intense gravitational waves. As they spiral closer to each other, these waves become more intense. At some point they should become so intense that direct detection by their effect on objects on Earth or in space is possible. This direct detection is the goal of several large-scale experiments.[88]
The only difficulty is that most systems like the Hulse–Taylor binary are so far away. The amplitude of waves given off by the Hulse–Taylor binary at Earth would be roughly h ≈ 10−26. There are some sources, however, that astrophysicists expect to find that produce much greater amplitudes of h ≈ 10−20. At least eight other binary pulsars have been discovered.[89]
Difficulties
Gravitational waves are not easily detectable. When they reach the Earth, they have a small amplitude with strain approximately 10−21, meaning that an extremely sensitive detector is needed, and that other sources of noise can overwhelm the signal.[90] Gravitational waves are expected to have frequencies 10−16 Hz < f < 104 Hz.[91]
Ground-based detectors
Though the Hulse–Taylor observations were very important, they give only indirect evidence for gravitational waves. A more conclusive observation would be a direct measurement of the effect of a passing gravitational wave, which could also provide more information about the system that generated it. Any such direct detection is complicated by the extraordinarily small effect the waves would produce on a detector. The amplitude of a spherical wave will fall off as the inverse of the distance from the source (the 1/R term in the formulas for h above). Thus, even waves from extreme systems like merging binary black holes die out to very small amplitudes by the time they reach the Earth. Astrophysicists expect that some gravitational waves passing the Earth may be as large as h ≈ 10−20, but generally no bigger.[92]
Resonant antennas
A simple device theorised to detect the expected wave motion is called a
There are currently two detectors focused on the higher end of the gravitational wave spectrum (10−7 to 105 Hz): one at
Interferometers
A more sensitive class of detector uses a laser
Even with such long arms, the strongest gravitational waves will only change the distance between the ends of the arms by at most roughly 10−18 m. LIGO should be able to detect gravitational waves as small as h ~ 5×10−22. Upgrades to LIGO and Virgo should increase the sensitivity still further. Another highly sensitive interferometer, KAGRA, which is located in the Kamioka Observatory in Japan, is in operation since February 2020. A key point is that a tenfold increase in sensitivity (radius of 'reach') increases the volume of space accessible to the instrument by one thousand times. This increases the rate at which detectable signals might be seen from one per tens of years of observation, to tens per year.[99]
Interferometric detectors are limited at high frequencies by
Einstein@Home
The simplest gravitational waves are those with constant frequency. The waves given off by a spinning, non-axisymmetric neutron star would be approximately
The Einstein@Home project is a distributed computing project similar to SETI@home intended to detect this type of gravitational wave. By taking data from LIGO and GEO, and sending it out in little pieces to thousands of volunteers for parallel analysis on their home computers, Einstein@Home can sift through the data far more quickly than would be possible otherwise.[100]
Space-based interferometers
Space-based interferometers, such as
Using pulsar timing arrays
Pulsars are rapidly rotating stars. A pulsar emits beams of radio waves that, like lighthouse beams, sweep through the sky as the pulsar rotates. The signal from a pulsar can be detected by radio telescopes as a series of regularly spaced pulses, essentially like the ticks of a clock. GWs affect the time it takes the pulses to travel from the pulsar to a telescope on Earth. A pulsar timing array uses millisecond pulsars to seek out perturbations due to GWs in measurements of the time of arrival of pulses to a telescope, in other words, to look for deviations in the clock ticks. To detect GWs, pulsar timing arrays search for a distinct quadrupolar pattern of correlation and anti-correlation between the time of arrival of pulses from different pulsar pairs as a function of their angular separation in the sky.[103] Although pulsar pulses travel through space for hundreds or thousands of years to reach us, pulsar timing arrays are sensitive to perturbations in their travel time of much less than a millionth of a second.
The most likely source of GWs to which pulsar timing arrays are sensitive are supermassive black hole binaries, which form from the collision of galaxies.
Globally there are three active pulsar timing array projects. The
In June 2023, NANOGrav published the 15-year data release, which contained the first evidence for a stochastic gravitational wave background. In particular, it included the first measurement of the Hellings-Downs curve, the tell-tale sign of the gravitational wave origin of the observed background.[106][107]
Primordial gravitational wave
Primordial gravitational waves are gravitational waves observed in the
LIGO and Virgo observations
On 11 February 2016, the
Since then LIGO and Virgo have reported more gravitational wave observations from merging black hole binaries.
On 16 October 2017, the LIGO and Virgo collaborations announced the first-ever detection of gravitational waves originating from the coalescence of a binary neutron star system. The observation of the
In 2021, the detection of the first two neutron star-black hole binaries by the LIGO and VIRGO detectors was published in the Astrophysical Journal Letters, allowing to first set bounds on the quantity of such systems. No neutron star-black hole binary had ever been observed using conventional means before the gravitational observation.[9]
Microscopic sources
In 1964 L. Halpern and B. Laurent theoretically proved that gravitational spin-2 electron transitions are possible in atoms. Compared to electric and magnetic transitions the emission probability is extremely low. Stimulated emission was discussed for increasing the efficiency of the process. Due to the lack of mirrors or resonators for gravitational waves, they determined that a single pass GASER (a kind of laser emitting gravitational waves) is practically unfeasible.[113]
In 1998 the possibility of a different implementation of the above theoretical analysis was proposed by Giorgio Fontana. The required coherence for a practical GASER could be obtained by Cooper pairs in superconductors that are characterized by a macroscopic collective wave-function. Cuprate high temperature superconductors are characterized by the presence of s-wave and d-wave[114] Cooper pairs. Transitions between s-wave and d-wave are gravitational spin-2. Out of equilibrium conditions can be induced by injecting s-wave Cooper pairs from a low temperature superconductor, for instance lead or niobium, which is pure s-wave, by means of a Josephson junction with high critical current. The amplification mechanism can be described as the effect of superradiance, and 10 cubic centimeters of cuprate high temperature superconductor seem sufficient for the mechanism to properly work. A detailed description of the approach can be found in "High Temperature Superconductors as Quantum Sources of Gravitational Waves: The HTSC GASER". Chapter 3 of this book.[115]
In fiction
An episode of the 1962 Russian science-fiction novel Space Apprentice by Arkady and Boris Strugatsky shows the experiment monitoring the propagation of gravitational waves at the expense of annihilating a chunk of asteroid 15 Eunomia the size of Mount Everest.[116]
In
In Greg Egan's 1997 novel Diaspora, the analysis of a gravitational wave signal from the inspiral of a nearby binary neutron star reveals that its collision and merger is imminent, implying a large gamma-ray burst is going to impact the Earth.
In Liu Cixin's 2006 Remembrance of Earth's Past series, gravitational waves are used as an interstellar broadcast signal, which serves as a central plot point in the conflict between civilizations within the galaxy.
See also
- 2017 Nobel Prize in Physics, which was awarded to three individual physicists for their role in the discovery of and testing for the waves
- Anti-gravity
- Artificial gravity
- First observation of gravitational waves
- Gravitational plane wave
- Gravitational field
- Gravitational-wave astronomy
- Gravitational wave background
- Gravitational-wave observatory
- Gravitomagnetism
- Graviton
- Hawking radiation, for gravitationally induced electromagnetic radiation from black holes
- HM Cancri
- LISA, DECIGO and BBO – proposed space-based detectors
- LIGO, Virgo interferometer, GEO600, KAGRA, and TAMA 300 – Ground-based gravitational-wave detectors
- Linearized gravity
- Peres metric
- pp-wave spacetime, for an important class of exact solutions modelling gravitational radiation
- PSR B1913+16, the first binary pulsardiscovered and the first experimental evidence for the existence of gravitational waves.
- Spin-flip, a consequence of gravitational wave emission from binary supermassive black holes
- Sticky bead argument, for a physical way to see that gravitational radiation should carry energy
- Tidal force
References
- ^ "Sur la dynamique de l'électron - Note de Henri Poincaré publiée dans les Comptes rendus de l'Académie des sciences de la séance du 5 juin 1905 - Membres de l'Académie des sciences depuis sa création" [On the dynamics of the electron - Note by Henri Poincaré published in the Reports of the Academy of Sciences of the session of June 5, 1905 - Members of the Academy of Sciences since its creation] (PDF). www.academie-sciences.fr (in French). Retrieved 3 November 2023.
- ISBN 978-0-521-23197-8.
- Bibcode:1916SPAW.......688E. Archived from the originalon 2016-01-15. Retrieved 2014-11-15.
- ^ Bibcode:1918SPAW.......154E. Archived from the originalon 2016-01-15. Retrieved 2014-11-15.
- ^ Finley, Dave. "Einstein's gravity theory passes toughest test yet: Bizarre binary star system pushes study of relativity to new limits". Phys.Org.
- ^ The Detection of Gravitational Waves using LIGO, B. Barish Archived 2016-03-03 at the Wayback Machine
- .
- ^ Chang, Kenneth (29 June 2021). "A Black Hole Feasted on a Neutron Star. 10 Days Later, It Happened Again – Astronomers had long suspected that collisions between black holes and dead stars occurred, but they had no evidence until a pair of recent detections". The New York Times. Retrieved 29 June 2021.
- ^ S2CID 235670241.
- Discovery Science.
- ISBN 978-0-521-88705-2.
- S2CID 6842810.
- ^ "LIGO, Virgo, and KAGRA raise their signal score to 90". www.aei.mpg.de. Max Planck Institute for Gravitational Physics. Retrieved 13 November 2021.
- S2CID 11804455.
- ^ ISBN 978-0-521-22285-3.
- ISBN 978-981-02-2749-4.
- ^ Taylor, Edwin F.; Wheeler, John Archibald (1991). Spacetime Physics (2nd ed.). p. 12.
- ^ "GW170817 Press Release". LIGO Lab – Caltech.
- ^ a b c Staff (17 March 2014). "BICEP2 2014 Results Release". National Science Foundation. Retrieved 18 March 2014.
- ^ a b c Clavin, Whitney (17 March 2014). "NASA Technology Views Birth of the Universe". NASA. Retrieved 17 March 2014.
- New York Times. Retrieved 17 March 2014.
- ^ Heaviside O. A gravitational and electromagnetic analogy, Electromagnetic Theory, 1893, vol.1 455–466 Appendix B
- ^ (PDF) Membres de l'Académie des sciences depuis sa création : Henri Poincare. Sur la dynamique de l' electron. Note de H. Poincaré. C.R. T.140 (1905) 1504–1508.
- ^ "page 1507" (PDF).
- ^ a b c d e f g h
Cervantes-Cota, J.L.; Galindo-Uribarri, S.; Smoot, G.F. (2016). "A Brief History of Gravitational Waves". Universe. 2 (3): 22. S2CID 2187981.
- ^ ISBN 978-1-4008-8274-8.
- Bibcode:1956AcPP...15..389P
- ^ David Robinson, Gravitation and general relativity at King's College London, European Physical Journal H 44, pp 181–270 (2019)
- ^ Skuse, Ben (2022-09-01). "Black Holes - Topic | Lindau Mediatheque". Lindau Nobel Mediatheque. Retrieved 2023-11-02.
- S2CID 121423215.
- ^ Nobel Prize Award (1993) Press Release The Royal Swedish Academy of Sciences.
- ^ doi:10.1086/159690.
- S2CID 22984747.
- ^ Gertsenshtein, M. E.; Pustovoit, V. I. (1962). "On the detection of low frequency gravitational waves". JETP. 43: 605–607.
- ^ Cho, Adrian (Oct. 3, 2017). "Ripples in space: U.S. trio wins physics Nobel for discovery of gravitational waves," Science. Retrieved 20 May 2019.
- ^ Cervantes-Cota, Jorge L., Galindo-Uribarri, Salvador, and Smoot, George F. (2016). "A Brief History of Gravitational Waves," Universe, 2, no. 3, 22. Retrieved 20 May 2019.
- ^ a b "Gravitational waves from black holes detected". BBC News. 11 February 2016.
- ^ S2CID 124959784.
- ^ "Gravitational waves detected 100 years after Einstein's prediction | NSF - National Science Foundation". www.nsf.gov. Retrieved 2016-02-11.
- ^ S2CID 182916902. Retrieved 2016-02-11.
- ^ "This collision was 50 times more powerful than all the stars in the universe combined".
- ^ a b c Scoles, Sarah (2016-02-11). "LIGO's First-Ever Detection of Gravitational Waves Opens a New Window on the Universe". Wired.
- ^ Clara Moskowitz (17 March 2014). "Gravity Waves from Big Bang Detected". Scientific American. Retrieved 21 March 2016.
- ^ Ian Sample (2014-06-04). "Gravitational waves turn to dust after claims of flawed analysis". the Guardian.
- ^ Rincon, Paul; Amos, Jonathan (3 October 2017). "Einstein's waves win Nobel Prize". BBC News. Retrieved 3 October 2017.
- ^ Overbye, Dennis (3 October 2017). "2017 Nobel Prize in Physics Awarded to LIGO Black Hole Researchers". The New York Times. Retrieved 3 October 2017.
- ^ Kaiser, David (3 October 2017). "Learning from Gravitational Waves". The New York Times. Retrieved 3 October 2017.
- ^ O'Callaghan, Jonathan (4 August 2023). "A Background 'Hum' Pervades the Universe. Scientists Are Racing to Find Its Source - Astronomers are now seeking to pinpoint the origins of an exciting new form of gravitational waves that was announced earlier this year". Scientific American. Archived from the original on 4 August 2023. Retrieved 4 August 2023.
- ^ "15 Years of Radio Data Reveals Evidence of Spacetime Murmur". NASA Jet Propulsion Laboratory. Retrieved 2023-06-30.
- ^ The second data release from the European Pulsar Timing Array III. Search for gravitational wave signals
- ^ "Ein neuer Zugang zum Universum".
- ^ LIGO press conference 11 February 2016
- ISBN 978-0-08-025072-4.
- ^ THE SCIENCE AND DETECTION OF GRAVITATIONAL WAVES; section: "Introduction, page 1" (PDF), retrieved 8 October 2022
- ^ "Gravitational Astrophysics Laboratory". science.gsfc/nasa.gov. Retrieved 20 September 2016.
- .
- .
- OCLC 319064125.
- ^ a b "Chapter 16 Gravity [sic] Waves" (PDF). AW Physics Macros. 9 September 2015. Archived from the original (PDF) on 29 January 2016.
- ^ "ESO Telescopes Observe First Light from Gravitational Wave Source – Merging neutron stars scatter gold and platinum into space". www.eso.org. Retrieved 18 October 2017.
- ^ LIGO Scientific Collaboration – FAQ; section: "Do we expect LIGO's advanced detectors to make a discovery, then?" and "What's so different about LIGO's advanced detectors?", retrieved 14 February 2016
- S2CID 125431568.
- S2CID 24225193.
- S2CID 5954627.
- S2CID 23409406.
- ^ "Neutron Star Crust Is Stronger than Steel". Space.com. 18 May 2009. Retrieved 2016-07-01.
- S2CID 15404149.
- S2CID 14314439.
- S2CID 17260029.
- S2CID 6860884.
- ISBN 978-0-7167-0344-0.
- ^
Lightman, A. P.; Press, W. H.; Price, R. H.; Teukolsky, S. A. (1975). "Problem 12.16". ISBN 978-0-691-08162-5.
- ^ a b Mack, Katie (2017-06-12). "Black Holes, Cosmic Collisions and the Rippling of Spacetime". Scientific American (blogs).
- ^ Update on Gravitational Wave Science from the LIGO-Virgo Scientific Collaborations (Video of the press conference), retrieved 27 September 2017
- ^ Gough, Evan (11 February 2016). "Gravitational Waves Discovered: A New Window on the Universe". Universe Today. Retrieved 30 March 2021.
- ^ Berry, Christopher (14 May 2015). "Listening to the gravitational universe: what can't we see?". University of Birmingham. University of Birmingham. Retrieved 29 November 2015.
- Bibcode:1976ZhPmR..23..326G. PACS numbers: 04.30. + x, 04.90. + e
- ^ Braginsky, V. B., Rudenko and Valentin, N. Section 7: "Generation of gravitational waves in the laboratory", Physics Report (Review section of Physics Letters), 46, No. 5. 165–200, (1978).
- ^ Li, Fangyu, Baker, R. M L, Jr., and Woods, R. C., "Piezoelectric-Crystal-Resonator High-Frequency Gravitational Wave Generation and Synchro-Resonance Detection", in the proceedings of Space Technology and Applications International Forum (STAIF-2006), edited by M.S. El-Genk, AIP Conference Proceedings, Melville NY 813: 2006.
- ^ Wall, SPACE.com, Mike. "Gravitational Waves Send Supermassive Black Hole Flying". Scientific American. Retrieved 2017-03-27.
- S2CID 27351189.
- ^ .
- Bibcode:2005ASPC..328...25W.
- S2CID 22984747.
- S2CID 119283147.
- ^ "Nobel Prizes and Laureates – NobelPrize.org". NobelPrize.org.
- S2CID 118307286.
- ^ Crashing Black Holes
- ^ Binary and Millisecond Pulsars Archived 2012-03-01 at the Wayback Machine
- ^ "Noise and Sensitivity". gwoptics: Gravitational wave E-book. University of Birmingham. Retrieved 10 December 2015.
- Bibcode:1995pnac.conf..160T.
- ^ Blair DG, ed. (1991). The detection of gravitational waves. Cambridge University Press.
- S2CID 76657516.
- Bibcode:2006rdgp.conf..415D.
- ISBN 9789812777386.
- ^ Cruise, Mike. "Research Interests". Astrophysics & Space Research Group. University of Birmingham. Archived from the original on 21 June 2017. Retrieved 29 November 2015.
- ^ High Frequency Relic Gravitational Waves Archived 2016-02-16 at the Wayback Machine. page 12
- ^ The idea of using laser interferometry for gravitational wave detection was first mentioned by Gerstenstein and Pustovoit 1963 Sov. Phys.–JETP 16 433. Weber mentioned it in an unpublished laboratory notebook. Rainer Weiss first described in detail a practical solution with an analysis of realistic limitations to the technique in R. Weiss (1972). "Electromagetically Coupled Broadband Gravitational Antenna". Quarterly Progress Report, Research Laboratory of Electronics, MIT 105: 54.
- S2CID 15200690.
- ^ "Einstein@Home".
- ^ "IOPscience - Focus on NANOGrav's 15 yr Data Set and the Gravitational Wave Background".
- ^ "After 15 years, pulsar timing yields evidence of cosmic gravitational wave background". 2022.
- ^
Hellings, R.W.; Downs, G.S. (1983). "Upper limits on the isotropic gravitational radiation background from pulsar timing analysis". doi:10.1086/183954.
- ^
Arzoumanian Z, et al. (NANOGrav Collaboration) (2018). "The NANOGrav 11-year Data Set: Pulsar-timing Constraints On The Stochastic Gravitational-wave Background". The Astrophysical Journal. 859 (1): 47. S2CID 89615050.
- ^
Hobbs, G.; et al. (2010). "The International Pulsar Timing Array project: using pulsars as a gravitational wave detector". S2CID 56073764.
- ISSN 2041-8205.
- ^ NANOGrav Collaboration (29 June 2023). "Focus on NANOGrav's 15 yr Data Set and the Gravitational Wave Background". The Astrophysical Journal Letters.
- ^ Kramer, Sarah (11 February 2016). "This collision was 50 times more powerful than all the stars in the universe combined". Business Insider. Retrieved 2020-09-06.
- ^ "Observation of Gravitational Waves from a Binary Black Hole Merger" (PDF). LIGO, with the collaboration of Virgo interferometer. 2016. Retrieved 2015-09-14.
- ISBN 9780198397960.
- S2CID 217163611.
- ^ "GW170817 Press Release". LIGO Lab | Caltech. Retrieved 2017-10-17.
- S2CID 121980464.
- ISBN 978-3-540-70695-3.
- )
- Bibcode:1963JETP...16..433G.
Further reading
- Bartusiak, Marcia. Einstein's Unfinished Symphony. Washington, DC: Joseph Henry Press, 2000.
- Chakrabarty, Indrajit (1999). "Gravitational Waves: An Introduction". arXiv:physics/9908041.
- Landau, L. D. and Lifshitz, E. M., The Classical Theory of Fields (Pergamon Press), 1987.
- Will, Clifford M. (2014). "The Confrontation between General Relativity and Experiment". PMID 28179848.
- ISBN 978-981-02-1820-1.
- Barish, Barry C.; Weiss, Rainer (1999). "LIGO and the Detection of Gravitational Waves". doi:10.1063/1.882861.
Bibliography
- ISBN 0-85274-037-9
- ISBN 0-226-11378-7
- Collins, Harry, Gravity's Kiss: The Detection of Gravitational Waves (The MIT Press, Cambridge Massachusetts, 2017). ISBN 978-0-262-03618-4.
- ISBN 0521231973.
- Grote, Hartmut, Gravitational Waves: A history of discovery (CRC Press, Taylor & Francis Group, Boca Raton/London/New York, 2020). ISBN 978-0-367-13681-9.
- ISBN 0-691-01933-9.
- ISBN 0-691-03323-4.
- Woolf, Harry, ed., Some Strangeness in the Proportion (Addison–Wesley, Reading, Massachusetts, 1980). ISBN 0-201-09924-1.
External links
- Laser Interferometer Gravitational Wave Observatory. LIGO Laboratory, operated by the California Institute of Technology and the Massachusetts Institute of Technology
- Gravitational Waves – Collected articles at Nature Journal
- Gravitational Waves – Collected articles Scientific American
- Video (94:34) – Scientific Talk on Discovery, Barry Barish, CERN (11 February 2016)
- Christina Sormani; C. Denson Hill; Paweł Nurowski; ISSN 1088-9477.