|Organization|| Sun Yat-sen University |
|Telescope style|| gravitational-wave observatory |
The TianQin Project (Chinese :天琴计划) is a proposed space-borne gravitational-wave observatory (gravitational-wave detector) consisting of three spacecrafts in Earth orbit. The TianQin project is being led by Professor Luo Jun (Chinese :罗俊), President of Sun Yat-sen University, and is based in the university's Zhuhai campus. Construction on project-related infrastructure, which will include a research building, ultra-quiet cave laboratory, and observation center, began in March 2016. The project is estimated to cost 15 billion RMB (US$2.3 billion), with a projected launch date in 2030s. In December 2019, China launched "Tianqin-1, its first satellite for space-based gravitational wave detection."
The project's name combines the Chinese words "Tian" (天), meaning sky or heavens, and "Qin" (琴), meaning stringed instrument. This name refers to the metaphorical concept of gravitational waves "plucking the strings" by causing fluctuations in the 100,000 kilometer laser beams stretching between each of the three TianQin spacecrafts.
The observatory will consist of three identical drag-free controlled spacecrafts in high Earth orbits at an altitude of about 100,000 km. The nominal source of the observatory is a white-dwarf binary RX J0806.3+1527 (also known as HM Cancri). This could serve as a good calibration source for the TianQin gravitational wave observatory. Similar configuration of geocentric orbit space-borne gravitational wave detectors have been developed since 2011, and was shown to have favorable properties for observing intermediate-mass and massive black-hole binaries.
Apart from Galactic binaries, the TianQin observatory can also detect sources like massive black hole binaries, extreme mass ratio inspirals, stellar-mass black hole binary inspirals, and stochastic gravitational wave background, etc.
The detection rate for massive black hole binaries is expected to be as high as about 60 per year,and TianQin would have accurate estimate to the source's parameters, which enable the potential for distinguishing the seed models for massive black holes, as well as issuing early warning for nearby mergers. It can also be used to test the no-hair theorem or constrain modified gravity.
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large observatories were built in the United States with the aim of detecting gravitational waves by laser interferometry. These observatories use mirrors spaced four kilometers apart which are capable of detecting a change of less than one ten-thousandth the charge diameter of a proton.
The Laser Interferometer Space Antenna (LISA) is a mission led by the European Space Agency to detect and accurately measure gravitational waves—tiny ripples in the fabric of space-time—from astronomical sources. LISA would be the first dedicated space-based gravitational wave detector. It aims to measure gravitational waves directly by using laser interferometry. The LISA concept has a constellation of three spacecraft arranged in an equilateral triangle with sides 2.5 million km long, flying along an Earth-like heliocentric orbit. The distance between the satellites is precisely monitored to detect a passing gravitational wave.
A stellar black hole is a black hole formed by the gravitational collapse of a star. They have masses ranging from about 5 to several tens of solar masses. The process is observed as a hypernova explosion or as a gamma ray burst. These black holes are also referred to as collapsars.
Einstein@Home is a volunteer distributed computing project that searches for signals from rotating neutron stars in data from the LIGO gravitational-wave detectors, from large radio telescopes, and from the Fermi Gamma-ray Space Telescope. Neutron stars are detected by their pulsed radio and gamma-ray emission as radio and/or gamma-ray pulsars. They also might be observable as continuous gravitational wave sources if they are rapidly rotating and non-axisymmetrically deformed. Einstein@Home examines radio telescope data from the Arecibo Observatory and has in the past analyzed data from Parkes Observatory, searching for radio pulsars. The project also analyses data from the Fermi Gamma-ray Space Telescope to discover gamma-ray pulsars. The project runs on the Berkeley Open Infrastructure for Network Computing (BOINC) software platform and uses free software released under the GNU General Public License, version 2. Einstein@Home is hosted by the University of Wisconsin–Milwaukee and the Max Planck Institute for Gravitational Physics. The project is supported by the American Physical Society (APS), the US National Science Foundation (NSF), and the Max Planck Society (MPG). The Einstein@Home project director is Bruce Allen.
Tests of general relativity serve to establish observational evidence for the theory of general relativity. The first three tests, proposed by Albert Einstein in 1915, concerned the "anomalous" precession of the perihelion of Mercury, the bending of light in gravitational fields, and the gravitational redshift. The precession of Mercury was already known; experiments showing light bending in accordance with the predictions of general relativity were performed in 1919, with increasingly precise measurements made in subsequent tests; and scientists claimed to have measured the gravitational redshift in 1925, although measurements sensitive enough to actually confirm the theory were not made until 1954. A more accurate program starting in 1959 tested general relativity in the weak gravitational field limit, severely limiting possible deviations from the theory.
Numerical relativity is one of the branches of general relativity that uses numerical methods and algorithms to solve and analyze problems. To this end, supercomputers are often employed to study black holes, gravitational waves, neutron stars and many other phenomena governed by Einstein's theory of general relativity. A currently active field of research in numerical relativity is the simulation of relativistic binaries and their associated gravitational waves. Other branches are also active.
The gravitational wave background is a random gravitational-wave signal potentially detectable by gravitational wave detection experiments. Since the background is supposed to be random it is completely determined by its statistical properties such as mean, variance etc.
Gravitational waves are disturbances in the curvature of spacetime, generated by accelerated masses, that propagate as waves outward from their source at the speed of light. They were proposed by Henri Poincaré in 1905 and subsequently predicted in 1916 by Albert Einstein on the basis of his general theory of relativity. Gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation. 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 – showing one of the ways the methods of classical physics are unable to explain phenomena associated with relativity.
A gravitational-wave observatory is any device designed to measure gravitational waves, tiny distortions of spacetime that were first predicted by Einstein in 1916. Gravitational waves are perturbations in the theoretical curvature of spacetime caused by accelerated masses. The existence of gravitational radiation is a specific prediction of general relativity, but is a feature of all theories of gravity that obey special relativity. Since the 1960s, gravitational-wave detectors have been built and constantly improved. The present-day generation of resonant mass antennas and laser interferometers has reached the necessary sensitivity to detect gravitational waves from sources in the Milky Way. Gravitational-wave observatories are the primary tool of gravitational-wave astronomy.
Gravitational-wave astronomy is an emerging branch of observational astronomy which aims to use gravitational waves to collect observational data about objects such as neutron stars and black holes, events such as supernovae, and processes including those of the early universe shortly after the Big Bang.
Primordial black holes are a hypothetical type of black hole that formed soon after the Big Bang. In the early universe, high densities and heterogeneous conditions could have led sufficiently dense regions to undergo gravitational collapse, forming black holes. Yakov Borisovich Zel'dovich and Igor Dmitriyevich Novikov in 1966 first proposed the existence of such black holes. The theory behind their origins was first studied in depth by Stephen Hawking in 1971. Since primordial black holes did not form from stellar gravitational collapse, their masses can be far below stellar mass (c. 2×1030 kg). Hawking calculated that primordial black holes could weigh as little as 10−8 kg.
A binary black hole (BBH) is a system consisting of two black holes in close orbit around each other. Like black holes themselves, binary black holes are often divided into stellar binary black holes, formed either as remnants of high-mass binary star systems or by dynamic processes and mutual capture, and binary supermassive black holes believed to be a result of galactic mergers.
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 dwarfs.
In astrophysics, an extreme mass ratio inspiral (EMRI) is the orbit of a relatively light object around a much heavier object, that gradually decays due the emission of gravitational waves. Such systems are likely to be found in the centers of galaxies, where stellar mass compact objects, such as stellar black holes and neutron stars, may be found orbiting a supermassive black hole. In the case of a black hole in orbit around another black hole this is an extreme mass ratio binary black hole. The term EMRI is sometimes used as a shorthand to denote the emitted gravitational waveform as well as the orbit itself.
The first direct observation of gravitational waves was made on 14 September 2015 and was announced by the LIGO and Virgo collaborations on 11 February 2016. Previously, gravitational waves had only been inferred indirectly, via their effect on the timing of pulsars in binary star systems. The waveform, detected by both LIGO observatories, matched the predictions of general relativity for a gravitational wave emanating from the inward spiral and merger of a pair of black holes of around 36 and 29 solar masses and the subsequent "ringdown" of the single resulting black hole. The signal was named GW150914. It was also the first observation of a binary black hole merger, demonstrating both the existence of binary stellar-mass black hole systems and the fact that such mergers could occur within the current age of the universe.
Manuela Campanelli is a distinguished professor in the School of Mathematical Sciences and in the Astrophysical Sciences and Technology Program at Rochester Institute of Technology (RIT), and the director of their Center for Computational Relativity and Gravitation. Her work focuses on the astrophysics of black holes and gravitational waves. In 2009 she was named a Fellow of the American Physical Society.
GW 170817 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017, originating from the shell elliptical galaxy NGC 4993. The GW was produced by the last minutes of two neutron stars spiralling closer to each other and finally merging, and is the first GW observation which has been confirmed by non-gravitational means. Unlike the five previous GW detections, which were of merging black holes not expected to produce a detectable electromagnetic signal, the aftermath of this merger was also seen by 70 observatories on 7 continents and in space, across the electromagnetic spectrum, marking a significant breakthrough for multi-messenger astronomy. The discovery and subsequent observations of GW 170817 were given the Breakthrough of the Year award for 2017 by the journal Science.
NGC 4993 is a lenticular galaxy located about 140 million light-years away in the constellation Hydra. It was discovered on 26 March 1789 by William Herschel and is a member of the NGC 4993 Group.
PyCBC is an open source software package primarily written in the Python programming language which is designed for use in gravitational-wave astronomy and gravitational-wave data analysis. PyCBC contains modules for signal processing, FFT, matched filtering, gravitational waveform generation, among other tasks common in gravitational-wave data analysis.
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