Gravitational-wave astronomy is an emerging branch of
observational astronomy
Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical ...
which aims to use
gravitational waves (minute distortions of
spacetime
In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why differ ...
predicted by
Albert Einstein
Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...
's theory of
general relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...
) to collect observational data about objects such as
neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...
s and
black holes, events such as
supernovae, and processes including those of the
early universe
The chronology of the universe describes the history and future of the universe according to Big Bang cosmology.
Research published in 2015 estimates the earliest stages of the universe's existence as taking place 13.8 billion years ago, wit ...
shortly after the
Big Bang.
Gravitational waves have a solid theoretical basis, founded upon the theory of relativity. They were first predicted by Einstein in 1916; although a specific consequence of general relativity, they are a common feature of all theories of gravity that obey
special relativity
In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates:
# The laws ...
. However, after 1916 there was a long debate whether the waves were actually physical, or artefacts of coordinate freedom in general relativity; this was not fully resolved until the 1950s. Indirect observational evidence for their existence first came in the late 1980s, from the monitoring of the
Hulse–Taylor binary pulsar (discovered 1974); the pulsar orbit was found to evolve exactly as would be expected for gravitational wave emission. Hulse and Taylor were awarded the 1993
Nobel Prize in Physics
)
, image = Nobel Prize.png
, alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then " ...
for this discovery.
On 11 February 2016 it was announced that the
LIGO
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large ...
collaboration had
directly observed gravitational waves for the first time in September 2015. The
second observation of gravitational waves was made on 26 December 2015 and announced on 15 June 2016.
Barry Barish
Barry Clark Barish (born January 27, 1936) is an American experimental physicist and Nobel Laureate. He is a Linde Professor of Physics, emeritus at California Institute of Technology and a leading expert on gravitational waves.
In 2017, Bar ...
,
Kip Thorne
Kip Stephen Thorne (born June 1, 1940) is an American theoretical physicist known for his contributions in gravitational physics and astrophysics. A longtime friend and colleague of Stephen Hawking and Carl Sagan, he was the Richard P. F ...
and
Rainer Weiss
Rainer "Rai" Weiss ( , ; born September 29, 1932) is an American physicist, known for his contributions in gravitational physics and astrophysics. He is a professor of physics emeritus at MIT and an adjunct professor at LSU. He is best known ...
were awarded the 2017 Nobel Prize in Physics for leading this work.
Observations
Ordinary gravitational waves' frequencies are very low and much harder to detect, while higher frequencies occur in more dramatic events and thus have become the first to be observed.
In addition to a merger of black holes, a binary
neutron star merger
A neutron star merger is a type of stellar collision.
It occurs in a fashion similar to the rare brand of type Ia supernovae resulting from merging white dwarf stars.
When two neutron stars orbit each other closely, they gradually spiral i ...
has been directly detected: a
gamma-ray burst
In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic explosions that have been observed in distant galaxies. They are the most energetic and luminous electromagnetic events since the Big Bang. Bursts can last from ten millise ...
(GRB) was detected by the orbiting
Fermi gamma-ray burst monitor
The Fermi Gamma-ray Space Telescope (FGST, also FGRST), formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is ...
on 2017 August 17 12:41:06 UTC, triggering an automated notice worldwide. Six minutes later a single detector at Hanford LIGO, a
gravitational-wave observatory
A gravitational-wave detector (used in a gravitational-wave observatory) is any device designed to measure tiny distortions of spacetime called gravitational waves. Since the 1960s, various kinds of gravitational-wave detectors have been built ...
, registered a gravitational-wave candidate occurring 2 seconds before the gamma-ray burst. This set of observations is consistent with a binary
neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...
merger,
[''Astrophysical Journal Letters'' (2017 October 16), Multi-messenger Observations of a Binary Neutron Star Merger]
/ref> as evidenced by a multi-messenger transient event which was signalled by gravitational-wave, and electromagnetic (gamma-ray burst, optical, and infrared)-spectrum sightings.
High frequency
In 2015, the LIGO
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large ...
project was the first to directly observe gravitational waves using laser interferometers. The LIGO detectors observed gravitational waves from the merger of two stellar-mass black holes, matching predictions of general relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...
. These observations demonstrated the existence of binary stellar-mass black hole systems, and were the first direct detection of gravitational waves and the first observation of a binary black hole merger. This finding has been characterized as revolutionary to science, because of the verification of our ability to use gravitational-wave astronomy to progress in our search and exploration of dark matter
Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not a ...
and the big bang.
There are several current scientific collaborations for observing gravitational waves. There is a worldwide network of ground-based detectors, these are kilometre-scale laser interferometers including: the Laser Interferometer Gravitational-Wave Observatory
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large ...
(LIGO), a joint project between MIT
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...
, Caltech
The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...
and the scientists of the LIGO Scientific Collaboration
The LIGO Scientific Collaboration (LSC) is a scientific collaboration of international physics institutes and research groups dedicated to the search for gravitational waves.
History
The LSC was established in 1997, under the leadership of Barry ...
with detectors in Livingston, Louisiana
Livingston is the parish seat of Livingston Parish, Louisiana, United States. The population was 1,769 at the 2010 census.
Livingston hosts one of the two LIGO gravitational wave detector sites, the other one being located in Hanford, Washin ...
and Hanford, Washington
Hanford was a small agricultural community in Benton County, Washington, United States. It and White Bluffs were depopulated in 1943 in order to make room for the nuclear production facility known as the Hanford Site. The town was located in what ...
; Virgo
Virgo may refer to:
*Virgo (astrology), the sixth astrological sign of the zodiac
* Virgo (constellation), a constellation
*Virgo Cluster, a cluster of galaxies in the constellation Virgo
*Virgo Stellar Stream, remains of a dwarf galaxy
* Virgo Su ...
, at the European Gravitational Observatory
The European Gravitational Observatory (EGO) is a consortium established to manage the Virgo interferometric antenna and its related infrastructure, as well as to promote cooperation in the field of gravitational wave research in Europe. It was ...
, Cascina
Cascina () is a ''comune'' (municipality) in the Province of Pisa in the Italian region Tuscany, located about west of Florence and about southeast of Pisa.
Cascina is located on the left shore of the Arno River, on a markedly plain terrain. ...
, Italy; GEO600 in Sarstedt
Sarstedt is a town in the district of Hildesheim, Lower Saxony, Germany. It has approximately 18,500 inhabitants. Sarstedt is situated 20 km south of Hanover and 10 km north of Hildesheim. Sarstedt station is on the Hanoverian Southern ...
, Germany, and the Kamioka Gravitational Wave Detector (KAGRA), operated by the University of Tokyo
, abbreviated as or UTokyo, is a public research university located in Bunkyō, Tokyo, Japan. Established in 1877, the university was the first Imperial University and is currently a Top Type university of the Top Global University Project b ...
in the Kamioka Observatory
The is a neutrino and gravitational waves laboratory located underground in the Mozumi mine of the Kamioka Mining and Smelting Co. near the Kamioka section of the city of Hida in Gifu Prefecture, Japan. A set of groundbreaking neutrino experim ...
, Japan. LIGO and Virgo have both been upgraded to advanced configurations. Advanced LIGO began observations in 2015, detecting gravitational waves even though not having reached its design sensitivity yet. The more advanced KAGRA started observation on February 25, 2020. GEO600 is currently operational, but its sensitivity makes it unlikely to make an observation; its primary purpose is to trial technology.
Low frequency
An alternative means of observation is using pulsar timing arrays (PTAs). There are three consortia, the European Pulsar Timing Array
The European Pulsar Timing Array (EPTA) is a European collaboration to combine five 100-m class radio-telescopes to observe an array of pulsars with the specific goal of detecting gravitational waves. It is one of three pulsar timing array project ...
(EPTA), the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), and the Parkes Pulsar Timing Array
Parkes Observatory is a radio astronomy observatory, located north of the town of Parkes, New South Wales, Australia. It hosts Murriyang, the 64 m CSIRO Parkes Radio Telescope also known as "The Dish", along with two smaller radio telescopes. ...
(PPTA), which co-operate as the International Pulsar Timing Array The International Pulsar Timing Array (IPTA) is a multi-institutional, multi-telescope collaboration comprising the European Pulsar Timing Array (EPTA), the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the Parkes Pulsa ...
. These use existing radio telescopes, but since they are sensitive to frequencies in the nanohertz range, many years of observation are needed to detect a signal and detector sensitivity improves gradually. Current bounds are approaching those expected for astrophysical sources.
Intermediate frequencies
Further in the future, there is the possibility of space-borne detectors. The European Space Agency has selected a gravitational-wave mission for its L3 mission, due to launch 2034, the current concept is the evolved Laser Interferometer Space Antenna
The Laser Interferometer Space Antenna (LISA) is a proposed space probe to detect and accurately measure gravitational waves—tiny ripples in the fabric of spacetime—from astronomical sources. LISA would be the first dedicated space-based gra ...
(eLISA). Also in development is the Japanese Deci-hertz Interferometer Gravitational wave Observatory (DECIGO).
Scientific value
Astronomy
Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...
has traditionally relied on electromagnetic radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) li ...
. Originating with the visible band, as technology advanced, it became possible to observe other parts of the electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...
, from radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmi ...
to gamma rays
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
. Each new frequency band gave a new perspective on the Universe and heralded new discoveries. During the 20th century, indirect and later direct measurements of high-energy, massive, particles provided an additional window into the cosmos. Late in the 20th century, the detection of solar neutrino
A solar neutrino is a neutrino originating from nuclear fusion in the Sun's core, and is the most common type of neutrino passing through any source observed on Earth at any particular moment. Neutrinos are elementary particles with extremely smal ...
s founded the field of neutrino astronomy
Neutrino astronomy is the branch of astronomy that observes astronomical objects with neutrino detectors in special observatories. Neutrinos are created as a result of certain types of radioactive decay, nuclear reactions such as those that take ...
, giving an insight into previously inaccessible phenomena, such as the inner workings of the Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
. The observation of gravitational waves provides a further means of making astrophysical observations.
Russell Hulse
Russell Alan Hulse (born November 28, 1950) is an American physicist and winner of the Nobel Prize in Physics, shared with his thesis advisor Joseph Hooton Taylor Jr., "''for the discovery of a new type of pulsar, a discovery that has opened up n ...
and Joseph Taylor were awarded the 1993 Nobel Prize in Physics
)
, image = Nobel Prize.png
, alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then " ...
for showing that the orbital decay of a pair of neutron stars, one of them a pulsar, fits general relativity's predictions of gravitational radiation. Subsequently, many other binary pulsars (including one double pulsar system) have been observed, all fitting gravitational-wave predictions. In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss
Rainer "Rai" Weiss ( , ; born September 29, 1932) is an American physicist, known for his contributions in gravitational physics and astrophysics. He is a professor of physics emeritus at MIT and an adjunct professor at LSU. He is best known ...
, Kip Thorne
Kip Stephen Thorne (born June 1, 1940) is an American theoretical physicist known for his contributions in gravitational physics and astrophysics. A longtime friend and colleague of Stephen Hawking and Carl Sagan, he was the Richard P. F ...
and Barry Barish
Barry Clark Barish (born January 27, 1936) is an American experimental physicist and Nobel Laureate. He is a Linde Professor of Physics, emeritus at California Institute of Technology and a leading expert on gravitational waves.
In 2017, Bar ...
for their role in the first detection of gravitational waves.
Gravitational waves provide complementary information to that provided by other means. By combining observations of a single event made using different means, it is possible to gain a more complete understanding of the source's properties. This is known as multi-messenger astronomy
Multi-messenger astronomy is astronomy based on the coordinated observation and interpretation of disparate "messenger" signals. Interplanetary probes can visit objects within the Solar System, but beyond that, information must rely on "extrasolar ...
. Gravitational waves can also be used to observe systems that are invisible (or almost impossible to detect) by any other means. For example, they provide a unique method of measuring the properties of black holes.
Gravitational waves can be emitted by many systems, but, to produce detectable signals, the source must consist of extremely massive objects moving at a significant fraction of the speed of light
The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...
. The main source is a binary of two compact objects. Example systems include:
* Compact binaries made up of two closely orbiting stellar-mass objects, such as white dwarf
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...
s, neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...
s or black holes. Wider binaries, which have lower orbital frequencies, are a source for detectors like LISA Lisa or LISA may refer to:
People
People with the mononym
* Lisa Lisa (born 1967), American actress and lead singer of the Cult Jam
* Lisa (Japanese musician, born 1974), stylized "LISA", Japanese singer and producer
* Lisa Komine (born 1978), J ...
. Closer binaries produce a signal for ground-based detectors like LIGO
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large ...
. Ground-based detectors could potentially detect binaries containing an intermediate mass black hole
An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range 102–105 solar masses: significantly more than stellar black holes but less than the 105–109 solar mass supermassive black holes. Several IMBH candidate obje ...
of several hundred solar masses.
* Supermassive black hole
A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical ob ...
binaries, consisting of two black holes with masses of 105–109 solar masses. Supermassive black holes are found at the centre of galaxies. When galaxies merge, it is expected that their central supermassive black holes merge too. These are potentially the loudest gravitational-wave signals. The most massive binaries are a source for PTAs. Less massive binaries (about a million solar masses) are a source for space-borne detectors like LISA Lisa or LISA may refer to:
People
People with the mononym
* Lisa Lisa (born 1967), American actress and lead singer of the Cult Jam
* Lisa (Japanese musician, born 1974), stylized "LISA", Japanese singer and producer
* Lisa Komine (born 1978), J ...
.
* Extreme-mass-ratio systems of a stellar-mass compact object orbiting a supermassive black hole. These are sources for detectors like LISA Lisa or LISA may refer to:
People
People with the mononym
* Lisa Lisa (born 1967), American actress and lead singer of the Cult Jam
* Lisa (Japanese musician, born 1974), stylized "LISA", Japanese singer and producer
* Lisa Komine (born 1978), J ...
. Systems with highly eccentric orbits produce a burst of gravitational radiation as they pass through the point of closest approach; systems with near-circular orbits, which are expected towards the end of the inspiral, emit continuously within LISA's frequency band. Extreme-mass-ratio inspirals can be observed over many orbits. This makes them excellent probes of the background spacetime
In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why differ ...
geometry, allowing for precision tests of general relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...
.
In addition to binaries, there are other potential sources:
* Supernovae generate high-frequency bursts of gravitational waves that could be detected with LIGO
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large ...
or Virgo
Virgo may refer to:
*Virgo (astrology), the sixth astrological sign of the zodiac
* Virgo (constellation), a constellation
*Virgo Cluster, a cluster of galaxies in the constellation Virgo
*Virgo Stellar Stream, remains of a dwarf galaxy
* Virgo Su ...
.
* Rotating neutron stars are a source of continuous high-frequency waves if they possess axial asymmetry.
* Early universe processes, such as inflation
In economics, inflation is an increase in the general price level of goods and services in an economy. When the general price level rises, each unit of currency buys fewer goods and services; consequently, inflation corresponds to a reduct ...
or a phase transition
In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states o ...
.
* Cosmic string
Cosmic strings are hypothetical 1-dimensional topological defects which may have formed during a symmetry-breaking phase transition in the early universe when the topology of the vacuum manifold associated to this symmetry breaking was not simp ...
s could also emit gravitational radiation if they do exist. Discovery of these gravitational waves would confirm the existence of cosmic strings.
Gravitational waves interact only weakly with matter. This is what makes them difficult to detect. It also means that they can travel freely through the Universe, and are not absorbed or scattered like electromagnetic radiation. It is therefore possible to see to the center of dense systems, like the cores of supernovae or the Galactic Center
The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ra ...
. It is also possible to see further back in time than with electromagnetic radiation, as the early universe
The chronology of the universe describes the history and future of the universe according to Big Bang cosmology.
Research published in 2015 estimates the earliest stages of the universe's existence as taking place 13.8 billion years ago, wit ...
was opaque to light prior to recombination, but transparent to gravitational waves.
The ability of gravitational waves to move freely through matter also means that gravitational-wave detector
A gravitational-wave detector (used in a gravitational-wave observatory) is any device designed to measure tiny distortions of spacetime called gravitational waves. Since the 1960s, various kinds of gravitational-wave detectors have been built ...
s, unlike telescope
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observ ...
s, are not pointed to observe a single field of view
The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.
Human ...
but observe the entire sky. Detectors are more sensitive in some directions than others, which is one reason why it is beneficial to have a network of detectors. Directionalization is also poor, due to the small number of detectors.
In cosmic inflation
Cosmic inflation, a hypothesized period when the universe rapidly expanded during the first 10−36 seconds after the Big Bang, would have given rise to gravitational waves; that would have left a characteristic imprint in the polarization of the CMB radiation.
It is possible to calculate the properties of the primordial gravitational waves from measurements of the patterns in the microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
radiation, and use those calculations to learn about the early universe.
Development
As a young area of research, gravitational-wave astronomy is still in development; however, there is consensus within the astrophysics community that this field will evolve to become an established component of 21st century multi-messenger astronomy
Multi-messenger astronomy is astronomy based on the coordinated observation and interpretation of disparate "messenger" signals. Interplanetary probes can visit objects within the Solar System, but beyond that, information must rely on "extrasolar ...
.[
Gravitational-wave observations complement observations in the ]electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...
. These waves also promise to yield information in ways not possible via detection and analysis of electromagnetic waves. Electromagnetic waves can be absorbed and re-radiated in ways that make extracting information about the source difficult. Gravitational waves, however, only interact weakly with matter, meaning that they are not scattered or absorbed. This should allow astronomers to view the center of a supernova, stellar nebulae, and even colliding galactic cores in new ways.
Ground-based detectors have yielded new information about the inspiral phase and mergers of binary systems of two stellar mass black holes, and merger of two neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...
s. They could also detect signals from core-collapse supernova
A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...
e, and from periodic sources such as pulsars with small deformations. If there is truth to speculation about certain kinds of phase transition
In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states o ...
s or kink bursts from long cosmic string
Cosmic strings are hypothetical 1-dimensional topological defects which may have formed during a symmetry-breaking phase transition in the early universe when the topology of the vacuum manifold associated to this symmetry breaking was not simp ...
s in the very early universe (at cosmic time
Cosmic time, or cosmological time, is the time coordinate commonly used in the Big Bang models of physical cosmology. Such time coordinate may be defined for a homogeneous, expanding universe so that the universe has the same density everywhere ...
s around 10−25 seconds), these could also be detectable. Space-based detectors like LISA should detect objects such as binaries consisting of two white dwarfs
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fr ...
, and AM CVn stars (a white dwarf
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...
accreting matter from its binary partner, a low-mass helium star), and also observe the mergers of supermassive black hole
A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical ob ...
s and the inspiral of smaller objects (between one and a thousand solar masses) into such black holes. LISA should also be able to listen to the same kind of sources from the early universe as ground-based detectors, but at even lower frequencies and with greatly increased sensitivity.
Detecting emitted gravitational waves is a difficult endeavor. It involves ultra-stable high-quality lasers and detectors calibrated with a sensitivity of at least 2·10−22 Hz−1/2 as shown at the ground-based detector, GEO600. It has also been proposed that even from large astronomical events, such as supernova explosions, these waves are likely to degrade to vibrations as small as an atomic diameter.[See .]
See also
* Gravitational wave background
The gravitational wave background (also GWB and stochastic background) is a random gravitational-wave signal potentially detectable by gravitational wave detection experiments. Since the background is supposed to be statistically random, it has ...
* Gravitational-wave observatory
A gravitational-wave detector (used in a gravitational-wave observatory) is any device designed to measure tiny distortions of spacetime called gravitational waves. Since the 1960s, various kinds of gravitational-wave detectors have been built ...
* List of gravitational wave observations
This is a list of observed/candidate gravitational wave events. Direct observation of gravitational waves, which commenced with the detection of an event by LIGO in 2015, constitutes part of gravitational wave astronomy. LIGO has played a role i ...
* Matched filter#In gravitational-wave astronomy
References
Further reading
*
*
*
*
*
External links
LIGO Scientific Collaboration
AstroGravS: Astrophysical Gravitational-Wave Sources Archive
Dennis Overbye
Dennis Overbye (born June 2, 1944, in Seattle, Washington) is a science writer specializing in physics and cosmology and is the cosmic affairs correspondent for '' The New York Times''.
Biography
Overbye received his B.S. in physics from M.I.T. ...
, NYT (11 February 2016).
Video (71:29) – Press Conference announcing discovery: "LIGO detects gravitational waves"
National Science Foundation
The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National ...
(11 February 2016).
Gravitational Wave Astronomy
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