Mordehai Milgrom | |
|---|---|
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| Born | 1946 |
| Nationality | Israeli |
| Alma mater | Hebrew University Weizmann Institute |
| Known for | Modified Newtonian dynamics |
| Scientific career | |
| Fields | Astrophysics |
| Institutions | Weizmann Institute |
Mordehai "Moti" Milgrom is an Israeli physicist and professor in the department of Particle Physics and Astrophysics at the Weizmann Institute in Rehovot, Israel.
He received his B.Sc. degree from the Hebrew University of Jerusalem in 1966. Later he studied at the Weizmann Institute of Science and completed his doctorate in 1972. Before 1980 he worked primarily on high-energy astrophysics and became well-known for his kinematical model of the star system SS 433. [1] [2] In the academic years 1980–1981 and 1985–1986 he was at the Institute for Advanced Study in Princeton. [3] In 1983, he proposed modified Newtonian dynamics (MOND) as an alternative to the dark matter and galaxy rotation curve problems, [4] [5] [6] although preliminary work and discussions on this subject started as early as 1981. [7]
Milgrom is a prominent proponent of the hypothesis that Newton's law of universal gravitation should be modified for very small accelerations, typically of the order of 10−11 g and less.
Milgrom is married and has three daughters.
In astronomy, dark matter is a hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravitational effects which cannot be explained by general relativity unless more matter is present than can be observed. Such effects occur in the context of formation and evolution of galaxies, gravitational lensing, the observable universe's current structure, mass position in galactic collisions, the motion of galaxies within galaxy clusters, and cosmic microwave background anisotropies.
The rotation curve of a disc galaxy is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It is typically rendered graphically as a plot, and the data observed from each side of a spiral galaxy are generally asymmetric, so that data from each side are averaged to create the curve. A significant discrepancy exists between the experimental curves observed, and a curve derived by applying gravity theory to the matter observed in a galaxy. Theories involving dark matter are the main postulated solutions to account for the variance.
A non-standard cosmology is any physical cosmological model of the universe that was, or still is, proposed as an alternative to the then-current standard model of cosmology. The term non-standard is applied to any theory that does not conform to the scientific consensus. Because the term depends on the prevailing consensus, the meaning of the term changes over time. For example, hot dark matter would not have been considered non-standard in 1990, but would have been in 2010. Conversely, a non-zero cosmological constant resulting in an accelerating universe would have been considered non-standard in 1990, but is part of the standard cosmology in 2010.
Abell 2218 is a large cluster of galaxies over 2 billion light-years away in the constellation Draco.
In astronomy, the Tully–Fisher relation (TFR) is a widely verified empirical relationship between the mass or intrinsic luminosity of a spiral galaxy and its asymptotic rotation velocity or emission line width. Since the observed brightness of a galaxy is distance-dependent, the relationship can be used to estimate distances to galaxies from measurements of their rotational velocity.
The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components:
A dark galaxy is a hypothesized galaxy with no stars. They received their name because they have no visible stars but may be detectable if they contain significant amounts of gas. Astronomers have long theorized the existence of dark galaxies, but there are no confirmed examples to date. Dark galaxies are distinct from intergalactic gas clouds caused by galactic tidal interactions, since these gas clouds do not contain dark matter, so they do not technically qualify as galaxies. Distinguishing between intergalactic gas clouds and galaxies is difficult; most candidate dark galaxies turn out to be tidal gas clouds. The best candidate dark galaxies to date include HI1225+01, AGC229385, and numerous gas clouds detected in studies of quasars.
Tensor–vector–scalar gravity (TeVeS), developed by Jacob Bekenstein in 2004, is a relativistic generalization of Mordehai Milgrom's Modified Newtonian dynamics (MOND) paradigm.
NGC 3227 is an intermediate spiral galaxy that is interacting with the dwarf elliptical galaxy NGC 3226. The two galaxies are one of several examples of a spiral with a dwarf elliptical companion that are listed in the Atlas of Peculiar Galaxies. Both galaxies may be found in the constellation Leo. It is a member of the NGC 3227 Group of galaxies, which is a member of the Leo II Groups, a series of galaxies and galaxy clusters strung out from the right edge of the Virgo Supercluster.
NGC 5548 is a Type I Seyfert galaxy with a bright, active nucleus. This activity is caused by matter flowing onto a 65 million solar mass (M☉) supermassive black hole at the core. Morphologically, this is an unbarred lenticular galaxy with tightly-wound spiral arms, while shell and tidal tail features suggest that it has undergone a cosmologically-recent merger or interaction event. NGC 5548 is approximately 245 million light years away and appears in the constellation Boötes. The apparent visual magnitude of NGC 5548 is approximately 13.3 in the V band.
The Bullet Cluster consists of two colliding clusters of galaxies. Strictly speaking, the name Bullet Cluster refers to the smaller subcluster, moving away from the larger one. It is at a comoving radial distance of 1.141 Gpc.
The Freeman law is a statement in astronomy which says that disk galaxies have the same surface brightness, Σ at the center. It was described in 1970 by Ken Freeman.
David Roy Merritt is an American astrophysicist.
Modified Newtonian dynamics (MOND) is a theory that proposes a modification of Newton's second law to account for observed properties of galaxies. Its primary motivation is to explain galaxy rotation curves without invoking dark matter, and is one of the most well-known theories of this class. However, it has not gained widespread acceptance, with the majority of astrophysicists supporting the Lambda-CDM model as providing the better fit to observations.
Stacy McGaugh is an American astronomer and professor in the Department of Astronomy at Case Western Reserve University in Cleveland, Ohio. His fields of specialty include low surface brightness galaxies, galaxy formation and evolution, tests of dark matter and alternative hypotheses, and measurements of cosmological parameters.
Bi-scalar tensor vector gravity theory (BSTV) is an extension of the tensor–vector–scalar gravity theory (TeVeS). TeVeS is a relativistic generalization of Mordehai Milgrom's Modified Newtonian Dynamics MOND paradigm proposed by Jacob Bekenstein. BSTV was proposed by R.H.Sanders. BSTV makes TeVeS more flexible by making a non-dynamical scalar field in TeVeS into a dynamical one.
AQUAL is a theory of gravity based on Modified Newtonian Dynamics (MOND), but using a Lagrangian. It was developed by Jacob Bekenstein and Mordehai Milgrom in their 1984 paper, "Does the missing mass problem signal the breakdown of Newtonian gravity?". "AQUAL" stands for "AQUAdratic Lagrangian", stemming from the fact that, in contrast to Newtonian gravity, the proposed Lagrangian is non-quadratic in the potential gradient .
Gauge vector–tensor gravity (GVT) is a relativistic generalization of Mordehai Milgrom's modified Newtonian dynamics (MOND) paradigm where gauge fields cause the MOND behavior. The former covariant realizations of MOND such as the Bekenestein's tensor–vector–scalar gravity and the Moffat's scalar–tensor–vector gravity attribute MONDian behavior to some scalar fields. GVT is the first example wherein the MONDian behavior is mapped to the gauge vector fields. The main features of GVT can be summarized as follows:
NGC 720 is an elliptical galaxy located in the constellation Cetus. It is located at a distance of circa 80 million light years from Earth, which, given its apparent dimensions, means that NGC 720 is about 110,000 light years across. It was discovered by William Herschel on October 3, 1785. The galaxy is included in the Herschel 400 Catalogue. It lies about three and a half degrees south and slightly east from zeta Ceti.
NGC 4636 is an elliptical galaxy located in the constellation Virgo. It is a member of the NGC 4753 Group of galaxies, which is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It is located at a distance of about 55 million light years from Earth, which, given its apparent dimensions, means that NGC 4636 is about 105,000 light years across.
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