Arlie Petters | |
---|---|
Born | Arlie Oswald Petters February 8, 1964 |
Alma mater | Hunter College Massachusetts Institute of Technology |
Known for | Mathematical theory of gravitational lensing |
Awards | Alfred P. Sloan Fellowship NSF CAREER Award Blackwell-Tapia Prize Most Excellent Order of the British Empire |
Scientific career | |
Doctoral advisors | Bertram Kostant David Spergel |
Arlie Oswald Petters, MBE (born February 8, 1964) is a Belizean-American mathematical physicist, who is the Benjamin Powell Professor of mathematics and a professor of physics and economics at Duke University. [1] Petters became the provost at New York University Abu Dhabi effective September 1, 2020. [2] Petters is a founder of mathematical astronomy, focusing on problems connected to the interplay of gravity and light and employing tools from astrophysics, cosmology, general relativity, high energy physics, differential geometry, singularities, and probability theory. [3] His monograph "Singularity Theory and Gravitational Lensing" developed a mathematical theory of gravitational lensing. Petters was also the dean of academic affairs for Trinity College of Arts and Sciences and associate vice provost for undergraduate education at Duke University (2016-2019). [4]
Petters was raised by his grandparents in the rural community of Dangriga, Belize (formerly Stann Creek Town, British Honduras). His mother immigrated to Brooklyn, New York, and married a U.S. citizen, with Arlie joining them when he was 14 years old. [5]
Petters earned a B.A./M.A. in Mathematics and Physics from Hunter College, CUNY in 1986 with a thesis on "The Mathematical Theory of General Relativity", and began his Ph.D. at the Massachusetts Institute of Technology Department of Mathematics in the same year. After two years of doctoral studies, he became an exchange scholar in the Princeton University Department of Physics in absentia from MIT. Petters earned his Ph.D. in mathematics in 1991 under advisors Bertram Kostant (MIT) and David Spergel (Princeton University). He remained at MIT for two years as an instructor of pure mathematics (1991–1993) and then joined the faculty at Princeton University in the Department of Mathematics. He was an assistant professor at Princeton for five years (1993–1998) before moving to Duke University. [4] [6]
Many media outlets have profiled Arlie Petters and his scholarship, including The New York Times , [5] NOVA, [7] The HistoryMakers (a digital archive of oral histories featuring African-Americans and preserved at the Library of Congress [8] ), [9] Big Think, [10] and Duke University's news outlet, The Chronicle. [11]
Petters is known for his work in the mathematical theory of gravitational lensing.
Over the ten-year period from 1991 to 2001, Petters systematically developed a mathematical theory of weak-deflection gravitational lensing, beginning with his 1991 MIT Ph.D. thesis on "Singularities in Gravitational Microlensing". [12] In a series of papers, he and his collaborators resolved an array of theoretical problems in weak-deflection gravitational lensing covering image counting, fixed-point images, image magnification, image time delays, local geometry of caustics, global geometry of caustics, wavefronts, caustic surfaces, and caustic surfing. [13] His work culminated in book, entitled Singularity Theory and Gravitational Lensing (Springer 2012), which he co-authored with Harold Levine and Joachim Wambganns. This book, which addressed the question, "What is the universe made of?", systematically created a framework of stability and genericity for k-plane gravitational lensing. [14] The book drew upon powerful tools from the theory of singularities and put the subject of weak-deflection k-plane gravitational lensing on a rigorous and unified mathematical foundation. [14]
Following his 1991–2001 body of mathematical lensing work, Petters turned to more astrophysical lensing issues from 2002 to 2005. In collaboration with astronomers, he applied some of the mathematical theory in [AP13] to help develop a practical diagnostic test for the presence of dark substructures in galaxies lensing quasars; [15] [16] classify the local astrometric (centroid) and photometric curves of an extended source when it crosses fold and cusp caustics due to generic lenses; [17] [18] predict the quantitative astrometric curve's shape produced by Galactic binary lenses. [17] [18] The classified local properties of the astrometric curves revealed a characteristic S-shape for fold crossings, parabolic and swallowtail features for cusp crossings, and a jump discontinuity for crossings over the fold arcs merging into a cusp. Petters, Levine, and Wambgamnns also developed a formula to calculate the size of the jump.
During the period from 2005 to 2007, Petters collaborated with astronomers and physicists to explore gravitational lensing in directions beyond its traditional confines in astronomy. In a series of three mathematical physics papers published written with the astronomer Charles R. Keeton, he utilized higher-order gravitational lensing effects by compact bodies to test different theories of gravity with the general theory of relativity of Einstein among them. These papers computed beyond the standard weak-deflection limit the first- and second-order corrections to the image positions, magnifications, and time delays due to lensing in general relativity and alternative gravitational theories describable within the PPN formalism, [19] and even determined lensing invariants for the PPN family of models. [20] Their findings were applied to the Galactic black hole, binary pulsars, and gravitational microlensing scenarios to make testable predictions about lensed images and their time delays. [19] Another paper took on the difficult issue of how to test hyperspace models like braneworld gravity that postulate an extra dimension to physical space. The paper developed a semi-classical wave theory of braneworld black hole lensing and used that theory along with braneworld cosmology to predict a testable signature of microscopic braneworld black holes on gamma-ray light. [21] [22] Additionally, in a 2007 paper, Petters and M.C. Werner found a system of equations that can be applied to test the Cosmic Censorship Hypothesis observationally using the realistic case of lensing by a Kerr black hole. [23] [24]
Petters's previous work (1991–2007) dealt with non-random gravitational lensing. Starting in 2008, his research program focused on developing a mathematical theory of random (stochastic) gravitational lensing. In two papers, Petters, Rider, and Teguia took first steps in creating a mathematical theory of stochastic gravitational microlensing. They characterized to several asymptotic orders the probability densities of random time delay functions, lensing maps, and shear maps in stochastic microlensing and determined a Kac-Rice type formula for the global expected number of images due to a general stochastic lens system. [25] [26] The work forms a concrete framework from which extensions to more general random maps can be made. In two additional papers, he and Aazami found geometric universal magnification invariants of higher-order caustics occurring in lensing and caustics produced by generic general maps up to codimension five. [27] [28] [29] The invariants hold with a probability of 1 for random lenses and thereby form important consistency checks for research on random image magnifications of sources near stable caustics.
Petters has served as director of the Reginaldo Howard Memorial Scholarship program at Duke University. [30] He has also been active in the African-American community particularly through his mentoring, recruiting, and lecturing. [31] [32] He has received several community service awards for his social outreach. [33] [34] Petters is the first tenured African-American professor in mathematics at Duke University. [33] He is very involved in the Belizean community and founded the Petters Research Institute [35] in 2005 to help train Belizean young people in STEM fields and foster STEM entrepreneurship. [36] [37] He has written five books, three of them science and mathematics problem-solving books for Belizean students. [38] [39] Some of his entrepreneurial work was conducted while he was a professor of business administration at Duke's Fuqua School of Business (2008–2017). [4] Petters also served the Government of Belize as chairman of the Council of Science Advisers to the prime minister of Belize (2010–2013). [40] [4]
Petters has received numerous awards and honors. [41] He was won an Alfred P. Sloan Research Fellowship in Mathematics (1998), [42] and a CAREER award from the National Science Foundation (1998), [43] and was the first winner of the Blackwell-Tapia Prize (2002). [44] He was selected in 2006 by the National Academy of Sciences to be part of a permanent Portrait Collection of Outstanding African-Americans in Science, Engineering, and Medicine. [45] In 2008 Petters was also included among the Human Relations Associates' list of "The Twenty-Five Greatest Scientists of African Ancestry,"going back to the eighteenth century. [46] He received an honorary Doctor of Science from his alma mater, Hunter College, in 2008. [47] Petters was named by the Queen of the United Kingdom in 2008 to membership in the Most Excellent Order of the British Empire. [48] In recognition of his scientific accomplishments and service to society, Petters's birthplace—Dangriga, Belize—honored him in 2009 by naming a road Dr. Arlie Petters Street. [49] He became in 2011 the first Belizean to receive the Caribbean American Heritage Award for Excellence in Science and Technology. [50] In 2012 he became a fellow of the American Mathematical Society [51] and the first Belizean American to be Grand Marshal of the Central American Day Parade in Los Angeles, where he received honors from the mayor and from the Confederation Centroamericana (COFECA). [52] [4] Petters was recognized by Mathematically Gifted & Black as a Black History Month 2017 Honoree. [53]
A black hole is a region of spacetime where gravity is so strong that nothing, not even light and other electromagnetic waves, is capable of possessing enough energy to escape it. Einstein's theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. A black hole has a great effect on the fate and circumstances of an object crossing it, but it has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly.
General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second-order partial differential equations.
Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large-scale structure of the Universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and eventually build the largest structures, clusters of galaxies. Clusters are then formed relatively recently between 10 billion years ago and now. Groups and clusters may contain ten to thousands of individual galaxies. The clusters themselves are often associated with larger, non-gravitationally bound, groups called superclusters.
Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics. It deals with environments in which neither gravitational nor quantum effects can be ignored, such as in the vicinity of black holes or similar compact astrophysical objects, such as neutron stars, as well as in the early stages of the universe moments after the Big Bang.
A gravitational lens is matter, such as a cluster of galaxies or a point particle, that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein's general theory of relativity. If light is treated as corpuscles travelling at the speed of light, Newtonian physics also predicts the bending of light, but only half of that predicted by general relativity.
A MAssive Compact Halo Object (MACHO) is a kind of astronomical body that might explain the apparent presence of dark matter in galactic halos. A MACHO is a body that emits little or no radiation and drifts through interstellar space unassociated with any planetary system. Since MACHOs are not luminous, they are hard to detect. MACHO candidates include black holes or neutron stars as well as brown dwarfs and unassociated planets. White dwarfs and very faint red dwarfs have also been proposed as candidate MACHOs. The term was coined by astrophysicist Kim Griest.
In modern models of physical cosmology, a dark matter halo is a basic unit of cosmological structure. It is a hypothetical region that has decoupled from cosmic expansion and contains gravitationally bound matter. A single dark matter halo may contain multiple virialized clumps of dark matter bound together by gravity, known as subhalos. Modern cosmological models, such as ΛCDM, propose that dark matter halos and subhalos may contain galaxies. The dark matter halo of a galaxy envelops the galactic disc and extends well beyond the edge of the visible galaxy. Thought to consist of dark matter, halos have not been observed directly. Their existence is inferred through observations of their effects on the motions of stars and gas in galaxies and gravitational lensing. Dark matter halos play a key role in current models of galaxy formation and evolution. Theories that attempt to explain the nature of dark matter halos with varying degrees of success include cold dark matter (CDM), warm dark matter, and massive compact halo objects (MACHOs).
Gravitational microlensing is an astronomical phenomenon caused by the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit much light (stars) or large objects that block background light. These objects make up only a minor portion of the mass of a galaxy. Microlensing allows the study of objects that emit little or no light.
The Optical Gravitational Lensing Experiment (OGLE) is a Polish astronomical project based at the University of Warsaw that runs a long-term variability sky survey (1992–present). The main goals are the detection and classification of variable stars, discovery of microlensing events, dwarf novae, and studies of the structure of the Galaxy and the Magellanic Clouds. Since the project began in 1992, it has discovered a multitude of extrasolar planets, together with the first planet discovered using the transit method (OGLE-TR-56b) and gravitational microlensing. The project has been led by professor Andrzej Udalski since its inception.
Microlensing Observations in Astrophysics (MOA) is a collaborative project between researchers in New Zealand and Japan, led by Professor Yasushi Muraki of Nagoya University. They use microlensing to observe dark matter, extra-solar planets, and stellar atmospheres from the Southern Hemisphere. The group concentrates especially on the detection and observation of gravitational microlensing events of high magnification, of order 100 or more, as these provide the greatest sensitivity to extrasolar planets. They work with other groups in Australia, the United States and elsewhere. Observations are conducted at New Zealand's Mt. John University Observatory using a 1.8 m (70.9 in) reflector telescope built for the project.
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.
In classical theories of gravitation, the changes in a gravitational field propagate. A change in the distribution of energy and momentum of matter results in subsequent alteration, at a distance, of the gravitational field which it produces. In the relativistic sense, the "speed of gravity" refers to the speed of a gravitational wave, which, as predicted by general relativity and confirmed by observation of the GW170817 neutron star merger, is equal to the speed of light (c).
Jürgen Ehlers was a German physicist who contributed to the understanding of Albert Einstein's theory of general relativity. From graduate and postgraduate work in Pascual Jordan's relativity research group at Hamburg University, he held various posts as a lecturer and, later, as a professor before joining the Max Planck Institute for Astrophysics in Munich as a director. In 1995, he became the founding director of the newly created Max Planck Institute for Gravitational Physics in Potsdam, Germany.
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.
The Cloverleaf quasar is a bright, gravitationally lensed quasar. It receives its name because of gravitational lensing spitting the single quasar into four images.
The Microlensing Follow-Up Network is an informal group of observers who monitor high magnification gravitational microlensing events in the Milky Way's Galactic Bulge. Its goal is to detect extrasolar planets via microlensing of the parent star by the planet. μFUN is a follow-up network - they monitor microlensing events identified by survey groups such as OGLE and Microlensing Observations in Astrophysics (MOA).
Relativistic images are images of gravitational lensing which result due to light deflections by angles .
Robert J. Nemiroff is an Astrophysicist and Professor of Physics at Michigan Technological University. He received his Ph.D. from the University of Pennsylvania in Astronomy and Astrophysics in 1987 and his B.S. from Lehigh University in Engineering Physics in 1982. He is an active researcher with interests that include gamma-ray bursts, gravitational lensing, and cosmology, and is the cofounder and coeditor of Astronomy Picture of the Day (APOD), the home page of which receives over a million hits a day, approximately 20% of nasa.gov traffic. He is married and has one daughter.
MACS J1149 Lensed Star 1, also known as Icarus, is a blue supergiant star observed through a gravitational lens. It is the seventh most distant individual star to have been detected so far, at approximately 14 billion light-years from Earth. Light from the star was emitted 4.4 billion years after the Big Bang. According to co-discoverer Patrick Kelly, the star is at least a hundred times more distant than the next-farthest non-supernova star observed, SDSS J1229+1122, and is the first magnified individual star seen.
Dr. Sun Hong Rhie was a Korean–American astrophysicist best known for her foundational contributions to the theory of gravitational microlensing, a technique for the discovery of exoplanets.
{{cite web}}
: CS1 maint: unfit URL (link){{cite web}}
: Missing or empty |title=
(help)