Reva Kay Williams | |
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Nationality | American |
Education | Malcolm X College A.A. in liberal arts, 1977 Northwestern University BA in astronomy & physics, 1980 Indiana University Bloomington MA in astrophysics, 1990 Indiana University Bloomington Ph.D. in astrophysics, 1991 [1] |
Known for | First person to successfully work out the Penrose process [1] First Black American woman to receive a Ph.D. in theoretical astrophysics Frame-dragging Gravitomagnetism |
Scientific career | |
Fields | Astrophysics |
Institutions | University of Toledo University of Florida Bennett College |
Thesis | Extracting X-rays, gamma rays, and electron-positron pairs from supermassive Kerr black holes using the Penrose mechanism (1991) |
Doctoral advisor | Richard H. Durisen |
Reva Kay Williams is a theoretical astrophysicist. She is the first person to successfully work out the Penrose process using Einstein's Theory of Relativity to extract energy from black holes. Also, she is the first Black American woman to earn a PhD in theoretical astrophysics. Her work focuses on general relativistic astrophysics.
Williams was born in Memphis, Tennessee and moved to Chicago at the age of 6. She received an A.A. in liberal arts from Malcolm X College in 1977 and a B.A. in astronomy from Northwestern University in 1980. Williams completed both a M.A. and a Ph.D. at Indiana University Bloomington, and when she completed her degree in 1991 she became the first Black American woman to receive a doctorate in theoretical astrophysics. [1]
With the publication of her Ph.D. thesis in 1991, Williams became the first person to work out the Penrose process of black holes. [2] In 1995, Williams published a paper in Physical Review D of research from her Ph.D. thesis. [3] Her calculations explained that black hole jets are emitted as escaping tornado-like coils of high energy photons and relativistic electrons, and as black holes drag spacetime into rotation near their cores, they may also produce uneven jets. [4] [5]
In April 2004, Williams published a letter titled "A Word from a Black Female Relativistic Astrophysicist: Setting the Record Straight on Black Holes" addressing her experience with breakthrough black hole physics and not receiving appropriate citations and others taking credit for her work. [6]
Williams was awarded a National Research Council Ford postdoctoral minority fellowship and was a postdoctoral associate at the University of Florida from 1993-1996. [7] [8] In January 1997, she worked as a visiting assistant professor of physics at North Carolina Agricultural and Technical State University (North Carolina A&T), [8] and in 1998, she became an associate professor of astrophysics and director of the Center for Women and Science at Bennett College, remaining in that position until 2001. [8]
In 2000, Williams received a grant to work with Robert M. Hjellming in Aspen, Colorado and Socorro, New Mexico studying microquasars. At that time, she was considered as the only Black American female astrophysicist in the [United States], [9] and as of 2004 was one of the few women in the world researching black holes. [10]
In 2009, she was awarded a National Science Foundation grant to "investigate the jet structure and energy generation of quasars and other active galactic nuclei (AGNs), microquasars, and gamma-ray bursters, all of which are believed to be powered by rotating (Kerr) black holes." [11] [12]
Since 2009, Williams has been a research assistant professor at the University of Toledo. [13] [7] Her continuing research interests are relativistic astrophysics, general relativity, cosmology, and extragalactic astronomy. [8]
Williams gave a plenary speech at the astrobiology conference, AbSciCon, in the spring of 2022, organized by American Geophysical Union and NASA. [14]
A quasar is an extremely luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way. Quasars are usually categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.
Timeline of black hole physics
An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such excess, non-stellar emissions have been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an active galaxy. The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.
X-ray binaries are a class of binary stars that are luminous in X-rays. The X-rays are produced by matter falling from one component, called the donor, to the other component, called the accretor, which is either a neutron star or black hole. The infalling matter releases gravitational potential energy, up to 30 percent of its rest mass, as X-rays. The lifetime and the mass-transfer rate in an X-ray binary depends on the evolutionary status of the donor star, the mass ratio between the stellar components, and their orbital separation.
Messier 87 is a supergiant elliptical galaxy in the constellation Virgo that contains several trillion stars. One of the largest and most massive galaxies in the local universe, it has a large population of globular clusters—about 15,000 compared with the 150–200 orbiting the Milky Way—and a jet of energetic plasma that originates at the core and extends at least 1,500 parsecs, traveling at a relativistic speed. It is one of the brightest radio sources in the sky and a popular target for both amateur and professional astronomers.
A supermassive black hole is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (M☉). Black holes are a class of astronomical objects that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, including light. Observational evidence indicates that almost every large galaxy has a supermassive black hole at its center. For example, the Milky Way galaxy has a supermassive black hole at its center, corresponding to the radio source Sagittarius A*. Accretion of interstellar gas onto supermassive black holes is the process responsible for powering active galactic nuclei (AGNs) and quasars.
A blazar is an active galactic nucleus (AGN) with a relativistic jet directed very nearly towards an observer. Relativistic beaming of electromagnetic radiation from the jet makes blazars appear much brighter than they would be if the jet were pointed in a direction away from Earth. Blazars are powerful sources of emission across the electromagnetic spectrum and are observed to be sources of high-energy gamma ray photons. Blazars are highly variable sources, often undergoing rapid and dramatic fluctuations in brightness on short timescales. Some blazar jets appear to exhibit superluminal motion, another consequence of material in the jet traveling toward the observer at nearly the speed of light.
In astroparticle physics, an ultra-high-energy cosmic ray (UHECR) is a cosmic ray with an energy greater than 1 EeV (1018 electronvolts, approximately 0.16 joules), far beyond both the rest mass and energies typical of other cosmic ray particles.
A rotating black hole is a black hole that possesses angular momentum. In particular, it rotates about one of its axes of symmetry.
An astrophysical jet is an astronomical phenomenon where outflows of ionised matter are emitted as extended beams along the axis of rotation. When this greatly accelerated matter in the beam approaches the speed of light, astrophysical jets become relativistic jets as they show effects from special relativity.
The Penrose process is theorised by Sir Roger Penrose as a means whereby energy can be extracted from a rotating black hole. The process takes advantage of the ergosphere – a region of spacetime around the black hole dragged by its rotation faster than the speed of light, meaning that from the point of view of an outside observer any matter inside is forced to move in the direction of the rotation of the black hole.
GRS 1915+105 or V1487 Aquilae is an X-ray binary star system containing a main sequence star and a black hole. Transfer of material from the star to the black hole generates a relativistic jet, making this a microquasar system. The jet exhibits apparent superluminal motion.
Roger David Blandford, FRS, FRAS is a British theoretical astrophysicist, best known for his work on black holes.
The Blandford–Znajek process is a mechanism for the extraction of energy from a rotating black hole, introduced by Roger Blandford and Roman Znajek in 1977. This mechanism is the most preferred description of how astrophysical jets are formed around spinning supermassive black holes. This is one of the mechanisms that power quasars, or rapidly accreting supermassive black holes. Generally speaking, it was demonstrated that the power output of the accretion disk is significantly larger than the power output extracted directly from the hole, through its ergosphere. Hence, the presence of a poloidal magnetic field around the black hole is not determinant in its overall power output. It was also suggested that the mechanism plays a crucial role as a central engine for a gamma-ray burst.
Gravitoelectromagnetism, abbreviated GEM, refers to a set of formal analogies between the equations for electromagnetism and relativistic gravitation; specifically: between Maxwell's field equations and an approximation, valid under certain conditions, to the Einstein field equations for general relativity. Gravitomagnetism is a widely used term referring specifically to the kinetic effects of gravity, in analogy to the magnetic effects of moving electric charge. The most common version of GEM is valid only far from isolated sources, and for slowly moving test particles.
Frame-dragging is an effect on spacetime, predicted by Albert Einstein's general theory of relativity, that is due to non-static stationary distributions of mass–energy. A stationary field is one that is in a steady state, but the masses causing that field may be non-static — rotating, for instance. More generally, the subject that deals with the effects caused by mass–energy currents is known as gravitoelectromagnetism, which is analogous to the magnetism of classical electromagnetism.
Prajval Shastri is an astrophysicist, formerly at the Indian Institute of Astrophysics, Bangalore and specializes in the area of phenomenology of active galaxies driven by supermassive blackholes using multi-wavelength observations ranging from radio to X-ray wavelengths.
Katherine Mary Blundell is a Professor of Astrophysics at the University of Oxford and a supernumerary research fellow at St John's College, Oxford. Previously, she held a Royal Society University Research Fellowship, and fellowships from the Royal Commission for the Exhibition of 1851 and Balliol College, Oxford.
Direct collapse black holes (DCBHs) are high-mass black hole seeds that form from the direct collapse of a large amount of material. They putatively formed within the redshift range z=15–30, when the Universe was about 100–250 million years old. Unlike seeds formed from the first population of stars (also known as Population III stars), direct collapse black hole seeds are formed by a direct, general relativistic instability. They are very massive, with a typical mass at formation of ~105 M☉. This category of black hole seeds was originally proposed theoretically to alleviate the challenge in building supermassive black holes already at redshift z~7, as numerous observations to date have confirmed.
Aneta Siemiginowska is a Polish-American astrophysicist whose research involves high-energy cosmic objects including supermassive black hole, quasars, blazars, active galaxies, and astrophysical jets. She works at the Center for Astrophysics | Harvard & Smithsonian as a senior astrophysicist in the Chandra X-ray Center.