North American Nanohertz Observatory for Gravitational Waves
Encyclopedia
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) is a consortium of astronomers
who share a common goal of detecting gravitational wave
s via regular observations of an ensemble of millisecond pulsar
s using with the Green Bank
and Arecibo
radio telescopes. This project is being carried out in collaboration with international partners in the Parkes Pulsar Timing Array in Australia and the European Pulsar Timing Array
.
s are an important prediction from Einstein's general theory of relativity and expected to result from the bulk motion of matter, fluctuations during the early universe and the dynamics of space-time itself. Pulsars are rapidly rotating, highly magnetized neutron stars formed during the supernova
explosions of massive stars. They act as highly accurate clocks with a wealth of physical applications ranging from celestial mechanics, neutron star seismology, tests of strong-field gravity and Galactic astronomy.
The idea to use pulsars as gravitational wave detectors was originally proposed by Sazhin and Detweiler in the late 1970s. The idea is to treat the solar system barycenter and a distant pulsar as opposite ends of an imaginary arm in space. The pulsar acts as the reference clock at one end of the arm sending out regular signals which are monitored by an observer on the Earth. The effect of a passing gravitational wave would be to perturb the local space-time metric and cause a change in the observed rotational frequency of the pulsar.
Hellings and Downs subsequently extended this idea to an array of pulsars and found that a stochastic background of gravitational waves would produce a correlated signal for different angular separations on the sky. This work was limited in sensitivity by the precision and stability of the pulsar clocks in the array. Following the discovery of the first millisecond pulsar
in 1982, Foster and Donald C. Backer
were among the first astronomers to seriously improve the sensitivity to gravitational waves by applying the Hellings-Downs analysis to an array of highly stable millisecond pulsars.
In the past decade, the advent of state-of-the-art digital data acquisition systems, new radio
telescopes and receiver systems and the discoveries of many new pulsars has seen a significant advance in the sensitivity of the pulsar timing array to gravitational waves. A recent paper by Hobbs et al. summarizes the current state of the international effort.
(NSF) and the Research Corporation for Scientific Advancement
in the USA. The NSF recently awarded a $6.8M dollar grant to researchers within NANOGrav as part of their Partnerships for International Research and Education (PIRE) program. In their recent Decadal Survey of Astronomy and Astrophysics, the National Academies of Science named NANOGrav as one of eight mid-scale astrophysics projects recommended as high priorities for funding in the next decade.
who share a common goal of detecting gravitational wave
Gravitational wave
In physics, gravitational waves are theoretical ripples in the curvature of spacetime which propagates as a wave, traveling outward from the source. Predicted to exist by Albert Einstein in 1916 on the basis of his theory of general relativity, gravitational waves theoretically transport energy as...
s via regular observations of an ensemble of millisecond pulsar
Millisecond pulsar
A millisecond pulsar is a pulsar with a rotational period in the range of about 1-10 milliseconds. Millisecond pulsars have been detected in the radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The origin of millisecond pulsars is still unknown...
s using with the Green Bank
Green Bank Telescope
The Robert C. Byrd Green Bank Telescope is the world's largest fully steerable radio telescope and the world's largest land-based movable structure. It is part of the National Radio Astronomy Observatory site at Green Bank, West Virginia, USA. The telescope honors the name of the late Senator...
and Arecibo
Arecibo Observatory
The Arecibo Observatory is a radio telescope near the city of Arecibo in Puerto Rico. It is operated by SRI International under cooperative agreement with the National Science Foundation...
radio telescopes. This project is being carried out in collaboration with international partners in the Parkes Pulsar Timing Array in Australia and the European Pulsar Timing Array
European Pulsar Timing Array
The European Pulsar Timing Array 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...
.
Gravitational wave detection using pulsar timing
Gravitational waveGravitational wave
In physics, gravitational waves are theoretical ripples in the curvature of spacetime which propagates as a wave, traveling outward from the source. Predicted to exist by Albert Einstein in 1916 on the basis of his theory of general relativity, gravitational waves theoretically transport energy as...
s are an important prediction from Einstein's general theory of relativity and expected to result from the bulk motion of matter, fluctuations during the early universe and the dynamics of space-time itself. Pulsars are rapidly rotating, highly magnetized neutron stars formed during the supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
explosions of massive stars. They act as highly accurate clocks with a wealth of physical applications ranging from celestial mechanics, neutron star seismology, tests of strong-field gravity and Galactic astronomy.
The idea to use pulsars as gravitational wave detectors was originally proposed by Sazhin and Detweiler in the late 1970s. The idea is to treat the solar system barycenter and a distant pulsar as opposite ends of an imaginary arm in space. The pulsar acts as the reference clock at one end of the arm sending out regular signals which are monitored by an observer on the Earth. The effect of a passing gravitational wave would be to perturb the local space-time metric and cause a change in the observed rotational frequency of the pulsar.
Hellings and Downs subsequently extended this idea to an array of pulsars and found that a stochastic background of gravitational waves would produce a correlated signal for different angular separations on the sky. This work was limited in sensitivity by the precision and stability of the pulsar clocks in the array. Following the discovery of the first millisecond pulsar
Millisecond pulsar
A millisecond pulsar is a pulsar with a rotational period in the range of about 1-10 milliseconds. Millisecond pulsars have been detected in the radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The origin of millisecond pulsars is still unknown...
in 1982, Foster and Donald C. Backer
Backer
Backer as a Norwegian surname can refer to:* Agathe Backer-Grøndahl , Norwegian pianist and composer* Augustin de Backer , Roman Catholic bibliographer* Brad Backer, Australian rugby league footballer...
were among the first astronomers to seriously improve the sensitivity to gravitational waves by applying the Hellings-Downs analysis to an array of highly stable millisecond pulsars.
In the past decade, the advent of state-of-the-art digital data acquisition systems, new radio
telescopes and receiver systems and the discoveries of many new pulsars has seen a significant advance in the sensitivity of the pulsar timing array to gravitational waves. A recent paper by Hobbs et al. summarizes the current state of the international effort.
Funding sources
The research activities of NANOGrav are supported by a combination of single-investigator grants awarded through the Natural Sciences and Engineering Research Council (NSERC) in Candada, the National Science FoundationNational Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
(NSF) and the Research Corporation for Scientific Advancement
Research Corporation
The Research Corporation for Science Advancement is an organization in the United States devoted to the advancement of science, funding research projects in the physical sciences. It was also a major supporter of the research that led to the presentation of Interlingua in 1951...
in the USA. The NSF recently awarded a $6.8M dollar grant to researchers within NANOGrav as part of their Partnerships for International Research and Education (PIRE) program. In their recent Decadal Survey of Astronomy and Astrophysics, the National Academies of Science named NANOGrav as one of eight mid-scale astrophysics projects recommended as high priorities for funding in the next decade.