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In theories of quantum gravity, the graviton is the hypothetical quantum of gravity, an elementary particle that mediates the force of gravitational interaction. There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity. In string theory, believed by some to be a consistent theory of quantum gravity, the graviton is a massless state of a fundamental string.
In quantum mechanics, the Pauli exclusion principle states that two or more identical particles with half-integer spins cannot simultaneously occupy the same quantum state within a system that obeys the laws of quantum mechanics. This principle was formulated by Austrian physicist Wolfgang Pauli in 1925 for electrons, and later extended to all fermions with his spin–statistics theorem of 1940.
The following is a timeline of gravitational physics and general relativity.
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 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 to measure changes in length—over an effective span of 1120 km—of less than one ten-thousandth the charge diameter of a proton.
Einstein@Home is a volunteer computing project that searches for signals from spinning neutron stars in data from gravitational-wave detectors, from large radio telescopes, and from a gamma-ray 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 spinning and non-axisymmetrically deformed. The project was officially launched on 19 February 2005 as part of the American Physical Society's contribution to the World Year of Physics 2005 event.
The Max Planck Institute for Gravitational Physics is a Max Planck Institute whose research is aimed at investigating Einstein's theory of relativity and beyond: Mathematics, quantum gravity, astrophysical relativity, and gravitational-wave astronomy. The institute was founded in 1995 and is located in the Potsdam Science Park in Golm, Potsdam and in Hannover where it closely collaborates with the Leibniz University Hannover. Both the Potsdam and the Hannover parts of the institute are organized in three research departments and host a number of independent research groups.
An exotic star is a hypothetical compact star composed of exotic matter, and balanced against gravitational collapse by degeneracy pressure or other quantum properties.
A binary pulsar is a pulsar with a binary companion, often a white dwarf or neutron star. Binary pulsars are one of the few objects which allow physicists to test general relativity because of the strong gravitational fields in their vicinities. Although the binary companion to the pulsar is usually difficult or impossible to observe directly, its presence can be deduced from the timing of the pulses from the pulsar itself, which can be measured with extraordinary accuracy by radio telescopes.
The Virgo interferometer is a large Michelson interferometer designed to detect the gravitational waves predicted by general relativity. It is in Santo Stefano a Macerata, near the city of Pisa, Italy. The instrument has two arms that are three kilometres long and contain its mirrors and instrumentation inside an ultra-high vacuum.
Gravitational waves are transient displacements in a gravitational field—generated by the motion or acceleration of gravitating masses—that radiate outward from their source at the speed of light. They were first proposed by Oliver Heaviside in 1893 and then later by Henri Poincaré in 1905 as the gravitational equivalent of electromagnetic waves. In 1916, Albert Einstein demonstrated that gravitational waves result from his general theory of relativity as ripples in spacetime.
Gravitational-wave astronomy is a subfield of astronomy concerned with the detection and study of gravitational waves emitted by astrophysical sources.
The LIGO Scientific Collaboration (LSC) is a scientific collaboration of international physics institutes and research groups dedicated to the search for gravitational waves.
A neutron star merger is the stellar collision of neutron stars. When two neutron stars fall into mutual orbit, they gradually spiral inward due to the loss of energy emitted as gravitational radiation. When they finally meet, their merger leads to the formation of either a more massive neutron star, or—if the mass of the remnant exceeds the Tolman–Oppenheimer–Volkoff limit—a black hole. The merger can create a magnetic field that is trillions of times stronger than that of Earth in a matter of one or two milliseconds. These events are believed to create short gamma-ray bursts.
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 been inferred only 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.
GW170817 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, about 140 million light years away. The signal was produced by the last moments of the inspiral process of a binary pair of neutron stars, ending with their merger. It was the first GW observation to be confirmed by non-gravitational means. Unlike the five previous GW detections—which were of merging black holes and thus not expected to produce a detectable electromagnetic signal—the aftermath of this merger was seen across the electromagnetic spectrum by 70 observatories on 7 continents and in space, marking a significant breakthrough for multi-messenger astronomy. The discovery and subsequent observations of GW170817 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.
Michel Davier is a French physicist.
Ground-based interferometric gravitational-wave search refers to the use of extremely large interferometers built on the ground to passively detect gravitational wave events from throughout the cosmos. Most recorded gravitational wave observations have been made using this technique; the first detection, revealing the merger of two black holes, was made in 2015 by the LIGO sites.
References
- ↑ "TOM HENDERSON: UM researcher helps prove that Einstein was right". Crain's Detroit Business. Retrieved 2024-09-08.
- ↑ "UM Physics Professor and LIGO Researcher Keith Riles on Gravitational Waves". Detroit Public Radio. 13 February 2016. Retrieved 2024-09-08.
- 1 2 3 "Keith Riles". U-M LSA Physics. Retrieved 2024-08-12.
- ↑ "Keith Riles". IAU Individual Members. Retrieved 2024-08-12.
- ↑ "Welcome to the Michigan home page of Keith Riles". University of Michigan. Retrieved 2024-08-14.
- ↑ "Keith Riles". U-M LSA Physics. Retrieved 2024-08-12.
- ↑ "Rapidly Spinning Neutron Stars and Emission Mechanisms (lecture 1) by Keith Riles". YouTube. 8 July 2024. Retrieved 2024-08-12.
- ↑ "Gravitational Wave Astronomy by Prof. Keith Riles". YouTube. 18 December 2021. Retrieved 2024-08-12.
- ↑ "Keith Riles - Saturday Morning Physics". YouTube. 15 February 2016. Retrieved 2024-08-12.
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