relativistic astrophysics

relativistic astrophysics

(rel-ă-tă-viss -tik) High-energy astrophysics, concerned with the extreme energies, velocities, densities, etc., associated with celestial objects such as white dwarfs, neutron stars, black holes, and active galaxies, and with the very early Universe. It involves the theories of special and general relativity, quantum mechanics, and the physics of elementary particles.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Relativistic Astrophysics


the branch of astrophysics that studies astronomical phenomena and celestial bodies under conditions for which classical mechanics and Newton’s law of gravitation are inapplicable. These conditions include a speed close to that of light, extremely high values of pressure and energy density (reaching or exceeding the density of the rest mass multiplied by the square of the speed of light), and extremely high values of gravitational potential (close to the square of the speed of light). The special and general theories of relativity underlie relativistic astrophysics.

The first work whose contents addressed relativistic astrophysics appeared in 1916, when K. Schwarzschild theoretically investigated the gravitational field around a strongly compressed mass. He introduced the concept of the gravitational radius rg corresponding to a mass M: rg = 2GM/c2, where G is the gravitational constant and c is the speed of light (rg is equal to 3 km for the sun and to 1 cm for the earth). This concept played a major role in the subsequent development of relativistic astrophysics.

Superdense stars, whose mass is concentrated within a sphere of radius smaller than rg, have a number of extraordinary properties. Thus, a particle impinging on the star as it approaches the gravitational radius acquires a speed approaching that of light.

Relativistic time dilation becomes infinite near the gravitational radius. A distant observer having the necessary instruments would see that as t → ∞, a particle asymptotically approaches a sphere of radius equal to rg, but the observer would not be able to see how the particle would intersect the sphere. Energy cannot escape from within this sphere. Thus was laid the basis for the modern theory of “black holes.”

Ordinary stars of sufficiently large mass are transformed at the end of their evolution into neutron stars, in which the density of matter reaches 10l4-1015 g/cm3; this transformation was explained in the 1930’s and 1940’s by the American astronomers W. Baade and F. Zwicky, the Soviet physicist L. V. Landau, the American physicist R. Oppenheimer, and the Canadian physicist G. M. Volkoff. As a result, stars with a mass close to that of the sun are transformed into neutron stars with a radius of approximately 10 km and a gravitational potential reaching 0.3c2 at the surface. Later, the ways in which ordinary stars with a mass two to three times greater than that of the sun are transformed into black holes were also studied.

The rapid development of relativistic astrophysics in the 1960’s led to a purposeful search for possible manifestations of relativistic states of stars. It was found that stars in such a state can act as invisible satellites in binary systems where the second component is a normal star. Jets of gas captured from surrounding space and accelerated to a speed close to that of light can serve as a source of X-radiation on collision with the surface of a neutron star or on collision with another jet of gas. However, relativistic astrophysics gained wide recognition after the discovery in 1967 of pulsars, which are rapidly rotating neutron stars.

Sources of X-radiation within binary stars were discovered using instruments carried outside the earth’s atmosphere. Some of these sources have proved to be neutron stars with a strong magnetic field that emits directional fluxes of X-radiation. This radiation results from the flow of gas from the surface of a normal star in a binary system to the surface of a neutron star. In two cases it may be assumed with high probability that one of the components is a black hole, in whose gravitational field the gas flowing from the surface of the other component—the normal star—is heated and emits X rays. In an investigation of the process of the compression of a normal star into a neutron star, it was found that when the compression occurs, the magnetic field is amplified in inverse proportion to the surface area of the star, that is, by a factor of billions.

The theory of quasars has been worked out to a lesser degree. However, there is no doubt that the magnetic field, the internal motions of gas, and relativistic particles play a major role in these objects. A black hole also may be present at the center of a quasar. The study of cosmic rays and of the gamma radiation resulting from the interaction of protons and heavier nuclei in cosmic rays with interstellar matter is afforded a prominent place in relativistic astrophysics.

Explosions of supernovas accompanied by the formation of neutron stars and black holes and apparently leading to the ejection of high-speed particles, that is, cosmic rays, are also subjects of investigation in relativistic astrophysics. Relativistic astrophysics also studies gravitational waves.

Relativistic astrophysics closely borders on cosmology in its conclusions. Its problems are being studied intensively in the USSR, the USA, and Great Britain.


Zel’dovich, Ia. B., and I. D. Novikov. Reliativistskaia astrofizika. Moscow, 1967.
Zel’dovich, Ia. B., and I. D. Novikov. Teoriia tiagoteniia i evoliutsiia zvezd. Moscow, 1971.
Zel’dovich, Ia. B., and I. D. Novikov. Stroenie i evoliutsiia Vselennoi. Moscow, 1975.
Peebles, P. Fizicheskaia kosmologiia. Moscow, 1975. (Translated from English.) Ia. B. Zel’dovich
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The 86 papers are from plenary sessions and sessions on classical gravity and general relativity extensions; classical and quantum cosmology, dark matter, and dark energy; black holes and wormholes; strings, branes, higher spin fields, quantum gravity; extra dimensions and variation of constants; gravitational experiments; and relativistic astrophysics. ([umlaut] Ringgold, Inc., Portland, OR)
"Once the tidal disruption flare dims below some threshold luminosity that can be seen in observations, the window closes for that particular galaxy." In a recent paper submitted to the Astrophysical Journal, Bogdanovic, working with Roseanne Cheng (Center for Relativistic Astrophysics at Georgia Tech) and Pau Amaro-Seoane (Albert Einstein Institute in Potsdam, Germany), considered the tidal disruption of a red giant star by a supermassive black hole using computer modeling.
Green (Haverford College) was reporting on what became known as the first Texas Symposium on Relativistic Astrophysics. The term "black hole" was not yet in common usage, but theoretical work already suggested that collapsed stars were inevitable.
The predictions of general relativity have been shown to be consistent with observational data in relativistic astrophysics and cosmology.
Pons, lecturer at the University of Alicante's Relativistic Astrophysics Group and Director of the Department of Applied Physics, who led the work said: "This may be the first observational evidence of existence of the phase of nuclear 'pasta' inside neutron stars, which may allow that future missions of X-ray observatories can be used to define aspects of how nuclear interaction works, which is not yet entirely clear."
Remo Ruffini is president of the International Center for Relativistic Astrophysics, Italy.
The volume includes the "Scientific Cooperation Program Signed Between the International Center for Relativistic Astrophysics Network and the Government of the State of Ceara" (Brazil).
His work on White Dwarfs, Stellar structure and Dynamics, Hydrodynamic and Hydeomagnetic stability, Figures of equilibrium, GR and Relativistic Astrophysics as well as the mathematical theory of Black Holes go to reiterate the quote that information is just bits of data while Knowledge is putting them together and Wisdom is transcending them.
The 118 papers cover the sun, planets, and the interplanetary medium; our galaxy's stars, exoplanets, and the interstellar medium; extragalactic astrophysics and cosmology; dynamical astronomy and relativistic astrophysics; astronomical infrastructure, and history and education in astronomy.
Michelson and his Stanford colleague Aurelien Bouvier presented their results December 8 in Vancouver at the Texas Symposium on Relativistic Astrophysics. At press time, Fermi researchers were scheduled to report similar findings January 7 in Long Beach, Calif., at a meeting of the American Astronomical Society.
At a time when there were few other African-Americans in the field of science, Johnson earned a bachelor's degree in physics from Gettysburg College, and a master's in physics and a doctorate in relativistic astrophysics from New York University.

Full browser ?