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Hellings-Downs Curve
The Hellings-Downs curve (also known as the Hellings and Downs curve) is a theoretical tool used to establish the telltale signature that a galactic-scale pulsar timing array has detected Gravitational wave, gravitational waves, typically of wavelengths \lambda = 1 - 10\,\mathrm. The method entails searching for spatial correlations of the timing residuals from pairs of Pulsar, pulsars and comparing the data with the Hellings-Downs curve. When the data fit exceeds the Standard_deviation#Experiment,_industrial_and_hypothesis_testing, standard ''5 sigma'' threshold, the pulsar timing array can declare detection of gravitational waves. More precisely, the Hellings-Downs curve is the expected correlations of the timing residuals from pairs of pulsars as a function of their angular separation on the sky as seen from Earth. This theoretical correlation function assumes Einstein's general relativity and a gravitational wave background that is Isotropy, isotropic. Pulsar timing array r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Correlation Vs Angular Separation Between Pulsars
In statistics, correlation or dependence is any statistical relationship, whether causality, causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistics it usually refers to the degree to which a pair of variables are ''line (geometry), linearly'' related. Familiar examples of dependent phenomena include the correlation between the human height, height of parents and their offspring, and the correlation between the price of a good and the quantity the consumers are willing to purchase, as it is depicted in the demand curve. Correlations are useful because they can indicate a predictive relationship that can be exploited in practice. For example, an electrical utility may produce less power on a mild day based on the correlation between electricity demand and weather. In this example, there is a causality, causal relationship, because extreme weather causes people to use more ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spacetime
In physics, spacetime, also called the space-time continuum, is a mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Spacetime diagrams are useful in visualizing and understanding relativistic effects, such as how different observers perceive ''where'' and ''when'' events occur. Until the turn of the 20th century, the assumption had been that the three-dimensional geometry of the universe (its description in terms of locations, shapes, distances, and directions) was distinct from time (the measurement of when events occur within the universe). However, space and time took on new meanings with the Lorentz transformation and special theory of relativity. In 1908, Hermann Minkowski presented a geometric interpretation of special relativity that fused time and the three spatial dimensions into a single four-dimensional continuum now known as Minkowski space. This interpretation proved vital t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pulsars
A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Earth (similar to the way a lighthouse can be seen only when the light is pointed in the direction of an observer), and is responsible for the pulsed appearance of emission. Neutron stars are very dense and have short, regular rotational periods. This produces a very precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. Pulsars are one of the candidates for the source of ultra-high-energy cosmic rays (see also centrifugal mechanism of acceleration). Pulsars’ highly regular pulses make them very useful tools for astronomers. For example, observations of a pulsar in a binary neutron star system were used to indirectly confirm the existence of gravitational radiation. The first ext ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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. The 64 m dish was one of several radio antennae used to receive live television images of the Apollo 11 Moon landing. Its scientific contributions over the decades led the Australian Broadcasting Corporation, ABC to describe it as "the most successful scientific instrument ever built in Australia" after 40 years of operation. The Parkes Observatory is run by the CSIRO, Commonwealth Scientific and Industrial Research Organisation (CSIRO), as part of the Australia Telescope National Facility (ATNF) network of radio telescopes. It is frequently operated together with other CSIRO radio telescopes, principally the array of six dishes at the Australia Telescope Compact Array near Narrabri, New South Wales, Narrabri, and a single dish at Mopra O ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
North American Nanohertz Observatory For Gravitational Waves
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) is a consortium of astronomers who share a common goal of detecting gravitational waves via regular observations of an ensemble of millisecond pulsars using the Green Bank Telescope, Arecibo Observatory, the Very Large Array, and the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Future observing plans include up to 25% total time of the Deep Synoptic Array 2000. This project is being carried out in collaboration with international partners in the Parkes Pulsar Timing Array in Australia, the European Pulsar Timing Array, and the Indian Pulsar Timing Array as part of the International Pulsar Timing Array. Gravitational wave detection using pulsar timing Gravitational waves are an important prediction from Einstein's general theory of relativity and result from the bulk motion of matter, fluctuations during the early universe, and the dynamics of space-time itself. Pulsars are rapidly rotating, h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Millisecond Pulsar
A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio pulsar, radio, X-ray pulsar, X-ray, and gamma ray portions of the electromagnetic spectrum. The leading hypothesis for the origin of millisecond pulsars is that they are old, rapidly rotating neutron stars that have been spun up or "recycled" through Accretion (astrophysics), accretion of matter from a companion star in a close binary system. For this reason, millisecond pulsars are sometimes called recycled pulsars. Origins Millisecond pulsars are thought to be related to low-mass X-ray binary systems. It is thought that the X-rays in these systems are emitted by the accretion disk of a neutron star produced by the outer layers of a companion star that has overflowed its Roche lobe. The transfer of angular momentum from this accretion event can increase the rotation rate of the pulsar to hundreds of times per second, as is observed in mi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Donald C
Donald is a Scottish masculine given name. It is derived from the Gaelic name ''Dòmhnall''.. This comes from the Proto-Celtic *''Dumno-ualos'' ("world-ruler" or "world-wielder"). The final -''d'' in ''Donald'' is partly derived from a misinterpretation of the Gaelic pronunciation by English speakers. A short form of Donald is Don, and pet forms of Donald include Donnie and Donny. The feminine given name Donella is derived from Donald. ''Donald'' has cognates in other Celtic languages: Modern Irish ''Dónal'' (anglicised as ''Donal'' and ''Donall'');. Scottish Gaelic ''Dòmhnall'', ''Domhnull'' and ''Dòmhnull''; Welsh '' Dyfnwal'' and Cumbric ''Dumnagual''. Although the feminine given name '' Donna'' is sometimes used as a feminine form of ''Donald'', the names are not etymologically related. Variations Kings and noblemen Domnall or Domhnall is the name of many ancient and medieval Gaelic kings and noblemen: * Dyfnwal Moelmud (Dunvallo Molmutius), legendary kin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pulsar Timing Array
A pulsar timing array (PTA) is a set of galactic pulsars that is monitored and analyzed to search for correlated signatures in the pulse arrival times on Earth. As such, they are galactic-sized detectors. Although there are many applications for pulsar timing arrays, the best known is the use of an array of millisecond pulsars to detect and analyse long-wavelength (i.e., low-frequency) gravitational wave background. Such a detection would entail a detailed measurement of a gravitational wave (GW) signature, like the GW-induced quadrupolar correlation between arrival times of pulses emitted by different millisecond pulsar pairings that depends only on the pairings' angular separations in the sky. Larger arrays may be better for GW detection because the quadrupolar spatial correlations induced by GWs can be better sampled by many more pulsar pairings. With such a GW detection, millisecond pulsar timing arrays would open a new low-frequency window in gravitational-wave astronomy to p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Albert Einstein
Albert Einstein (14 March 187918 April 1955) was a German-born theoretical physicist who is best known for developing the theory of relativity. Einstein also made important contributions to quantum mechanics. His mass–energy equivalence formula , which arises from special relativity, has been called "the world's most famous equation". He received the 1921 Nobel Prize in Physics for . Born in the German Empire, Einstein moved to Switzerland in 1895, forsaking his German citizenship (as a subject of the Kingdom of Württemberg) the following year. In 1897, at the age of seventeen, he enrolled in the mathematics and physics teaching diploma program at the Swiss ETH Zurich, federal polytechnic school in Zurich, graduating in 1900. He acquired Swiss citizenship a year later, which he kept for the rest of his life, and afterwards secured a permanent position at the Swiss Patent Office in Bern. In 1905, he submitted a successful PhD dissertation to the University of Zurich. In 19 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pulsar Timing Array
A pulsar timing array (PTA) is a set of galactic pulsars that is monitored and analyzed to search for correlated signatures in the pulse arrival times on Earth. As such, they are galactic-sized detectors. Although there are many applications for pulsar timing arrays, the best known is the use of an array of millisecond pulsars to detect and analyse long-wavelength (i.e., low-frequency) gravitational wave background. Such a detection would entail a detailed measurement of a gravitational wave (GW) signature, like the GW-induced quadrupolar correlation between arrival times of pulses emitted by different millisecond pulsar pairings that depends only on the pairings' angular separations in the sky. Larger arrays may be better for GW detection because the quadrupolar spatial correlations induced by GWs can be better sampled by many more pulsar pairings. With such a GW detection, millisecond pulsar timing arrays would open a new low-frequency window in gravitational-wave astronomy to p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pulsar Timing Residuals From The Parkes Pulsar Timing Array
A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Earth (similar to the way a lighthouse can be seen only when the light is pointed in the direction of an observer), and is responsible for the pulsed appearance of emission. Neutron stars are very dense and have short, regular rotational periods. This produces a very precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. Pulsars are one of the candidates for the source of ultra-high-energy cosmic rays (see also centrifugal mechanism of acceleration). Pulsars’ highly regular pulses make them very useful tools for astronomers. For example, observations of a pulsar in a binary neutron star system were used to indirectly confirm the existence of gravitational radiation. The first extraso ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotropy
In physics and geometry, isotropy () is uniformity in all orientations. Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix ' or ', hence ''anisotropy''. ''Anisotropy'' is also used to describe situations where properties vary systematically, dependent on direction. Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented. Mathematics Within mathematics, ''isotropy'' has a few different meanings: ; Isotropic manifolds: A manifold is isotropic if the geometry on the manifold is the same regardless of direction. A similar concept is homogeneity. ; Isotropic quadratic form: A quadratic form ''q'' is said to be isotropic if there is a non-zero vector ''v'' such that ; such a ''v'' is an isotropic vector or null vector. In complex geometry, a line through the origin in the direction of an is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
