- Schwarzschild radius
The

**Schwarzschild radius**(sometimes historically referred to as the**gravitational radius**) is a characteristicradius associated with everymass . It is the radius for a given mass where, if that mass could be compressed to fit within that radius, no known force or degeneracy pressure could stop it from continuing to collapse into agravitational singularity . The term is used inphysics andastronomy , especially in the theory ofgravitation ,general relativity .In 1916,

Karl Schwarzschild obtained an exact solution [*K. Schwarzschild, "Uber das Gravitationsfeld eines Massenpunktes nach der Einsteinschen Theorie", "Sitzungsberichte der Deutschen Akademie der Wissenschaften zu Berlin, Klasse fur Mathematik, Physik, und Technik" (1916) pp 189.*] [*K. Schwarzschild, "Uber das Gravitationsfeld einer Kugel aus inkompressibler Flussigkeit nach der Einsteinschen Theorie", "Sitzungsberichte der Deutschen Akademie der Wissenschaften zu Berlin, Klasse fur Mathematik, Physik, und Technik" (1916) pp 424.*] toEinstein's field equation s for the gravitational field outside a non-rotating, spherically symmetric body (seeSchwarzschild metric ). The solution contained a term of the form $1/(2M-r)$; the value of $r$ making this term singular has come to be known as the "Schwarzschild radius". The physical significance of this singularity, and whether this singularity could ever occur in nature, was debated for many decades; a general acceptance of the possibility of ablack hole did not occur until the second half of the 20th century.The Schwarzschild radius of an object is proportional to the mass. Accordingly, the

Sun has a Schwarzschild radius of approximately 3 km, while theEarth 's is only about 9 mm, the size of apeanut .An object smaller than its Schwarzschild radius is called a

black hole . The surface at the Schwarzschild radius acts as anevent horizon in a non-rotating body. (Arotating black hole operates slightly differently.) Neither light nor particles can escape through this surface from the region inside, hence the name "black hole". The Schwarzschild radius of the (currently hypothesized)Supermassive black hole at ourGalactic Center would be approximately 7.8 million km. The Schwarzschild radius of a sphere with a uniform density equal to thecritical density is equal to the radius of thevisible universe . [*F. Melia, "The Edge of Infinity: Supermassive Black Holes in the Universe," Cambridge UniversityPress (2003) pp 124.*]**Formula for the Schwarzschild radius**The Schwarzschild radius is proportional to the mass, with a proportionality constant involving the

gravitational constant and the speed of light.The formula for the Schwarzschild radius can be found by setting theescape velocity to the speed of light, and is:

$r\_s\; =\; frac\{2Gm\}\{c^2\},$where

: $r\_s$ is the Schwarzschild radius,

: $G$ is the

gravitational constant ,: $m$ is the mass of the gravitating object, and

: $c$ is the

speed of light .For a solar mass black hole, the Schwarzschild radius is thus 2.96 km, and the Schwarzschild radius of any other black hole can then be found by:

$r\_s\; =\; 2.96\; frac\{M\}\{M\_\{odot$ km.This can be extended to show that an object of any density can be large enough to fall within its own Schwarzschild radius,:

$V\_s\; propto\; ho^\{-1.5\}.$where: $V\_s$ is the volume of the object, and

:

*$ho$*is its density.Note that although the result is correct, general relativity must be used to properly derive the Schwarzschild radius. It is only a coincidence that

Newtonian physics produces the same result.**Classification by Schwarzschild radius****upermassive black hole**If one accumulates matter of normal density (1000 kg/m³, for example, the density of water) up to about 150,000,000 times the mass of the Sun, such an accumulation will fall inside its own Schwarzschild radius and thus it would be a

supermassive black hole of 150,000,000 solar masses. (Supermassive black holes up to 18 billion solar masses have been observed [*cite news*] .) The supermassive black hole in the center of our galaxy (3.7 million solar masses) constitutes observationally the most convincing evidence for the existence of black holes in general.It is thought that large black holes like these don't form directly in one collapse of a cluster of stars.Instead they may start as a stellar-sized black hole and grow larger by the accretion of matter and other black holes. The larger the mass of a galaxy, the larger is the mass of the supermassive black hole in its center.

last = Bryner

first = Jenna

coauthors =

title = Colossal Black Hole Shatters the Scales

work =

pages =

language =

publisher = SPACE.COM

date = January 9, 2008

url = http://www.space.com/scienceastronomy/080109-aas-massive-black-holes.html

accessdate = 2008-04-02**tellar black hole**If one accumulates matter at

nuclear density (the density of the nucleus of an atom, about 10^{18}kg/m³;neutron star s also reach this density), such an accumulation would fall within its own Schwarzschild radius at about 3 solar masses and thus would be astellar black hole .**Primordial black hole**Conversely, a small mass has an extremely small Schwarzschild radius. A mass similar to Mount Everest has a Schwarzschild radius smaller than a

nanometre . Its average density at that size would be so high that no known mechanism could form such extremely compact objects. Such black holes might possibly be formed in an early stage of the evolution of the universe, just after theBig Bang , when densities were extremely high. Therefore these hypothetical baby black holes are calledprimordial black hole s.**History**The significance of the singularity at $2M=r$ was first raised by

Jacques Hadamard , who, during a conference in Paris in 1922, asked what might happen if a physical system could ever obtain this singularity.Albert Einstein insisted that it could not, pointing out the dire consequences for the universe, and jokingly referred to the singularity as the "Hadamard disaster". [*Hamed Moradi, " [*]*http://www.maths.monash.edu.au/~hmoradi/Honours_Essay_2004.pdf An Early History of Black Holes*] ", (2004) Monash UniversitySchwarzschild's original model of a star assumed an incompressible fluid; Einstein pointed out that this was an unreasonable assumption, as sound waves would propagate at infinite speed. In his own work, Einstein reconsidered a model of a star where the components of the star were orbiting masses, and showed that the orbital velocities would exceed the speed of light at the Schwarzschild radius. In 1939, he used this to argue that no such thing can happen, and so the singularity could not occur in nature. [

*A. Einstein, "On a Stationary System with Spherical Symmetry Consisting of Many Gravitating Masses", "Annals of Mathematics", (1939)*] The same year,Robert Oppenheimer andHartland Snyder considered a model of a dust cloud, where the dust particles of the cloud were moving radially, towards a single point, and showed that the dust particles could reach the singularity in finiteproper time . After passing the limit, Oppenheimer and Snyder noted thatlight cone s were directed inwards, and that no signal could escape outside. [*J.R. Oppenheimer, H. Snyder, "On Continued Gravitational Contraction", "Physical Review"*]**56**(1939) p455.**ee also***

black hole , a general survey

*Chandrasekhar limit , a second requirement for black hole formationClassification of black holes by type:

*Schwarzschild or static black hole

*rotating or Kerr black hole

*charged black hole or Newman black hole and Kerr-Newman black holeA classification of black holes by mass:

*micro black hole and extra-dimensional black hole

*primordial black hole , a hypothetical leftover of the Big Bang

*stellar black hole , which could either be a static black hole or a rotating black hole

*supermassive black hole , which could also either be a static black hole or a rotating black hole

*visible universe , if its density is thecritical density **References**

*Wikimedia Foundation.
2010.*

### Look at other dictionaries:

**Schwarzschild-Radius**— Der Ereignishorizont liegt im einfachsten Fall an der Grenze der äußeren Schwarzschild Metrik und stellt damit den Umfang eines Schwarzen Loches dar. Ein Beobachter, der im Unendlichen (d.h. aus einer flachen Region der Raumzeit) auf das Schwarze … Deutsch Wikipedia**Schwarzschild radius**— Ger. /shvahrddts shilt /; Eng. /shwawrts chuyld , shild/, Astron. the radius at which a gravitationally collapsing celestial body becomes a black hole. [1955 60; named after Karl Schwarzchild (1873 1916), German astronomer] * * * or gravitational … Universalium**Schwarzschild-Radius**— Schwạrzschild Radius, Astrophysik: Grenzradius einer sphärischen nicht rotierenden und nicht elektrisch geladenen Massenverteilung, bei dessen Unterschreitung ein emittiertes Photon (Lichtquant) nicht mehr entweichen kann. Für eine Masse M… … Universal-Lexikon**schwarzschild radius**— ˈshwȯrtˌshild , ˈs(h)wȯrtsˌchīld ; ˈshvärtˌshilt noun Usage: usually capitalized S Etymology: after Karl Schwarzschild died 1916 German astronomer : the radius of the spherical boundary within which a given mass (as of a star) must collapse to… … Useful english dictionary**Schwarzschild radius**— /ʃvɔtstʃaɪld ˈreɪdiəs/ (say shvawtschuyld raydeeuhs) noun the radius at which the outer boundaries of a black hole would start, which is where the escape velocity first and exactly equals the speed of light. {named after Karl Schwarzschild,… … Australian English dictionary**Schwarzschild radius**— noun The radius of an object such that, if all its mass were compressed within that radius, the escape velocity would equal the speed of light … Wiktionary**Schwarzschild**— ist der Familienname folgender Personen: Heinrich Schwarzschild (1803–1878), deutscher Arzt und Dichter Karl Schwarzschild (1873–1916), deutscher Astronom und Physiker Leopold Schwarzschild (1891–1950), deutscher Publizist Martin Schwarzschild… … Deutsch Wikipedia**Schwarzschild**— is a German surname meaning black sign or black shield and may refer to: * Karl Schwarzschild, (1873 1916), physicist and astronomer * Martin Schwarzschild, (1912 1997), astronomer * Roger Schwarzschild, linguistNamed after Karl Schwarzschild: *… … Wikipedia**Schwarzschild metric**— In Einstein s theory of general relativity, the Schwarzschild solution (or the Schwarzschild vacuum) describes the gravitational field outside a spherical, non rotating mass such as a (non rotating) star, planet, or black hole. It is also a good… … Wikipedia**Schwarzschild , Karl**— (1873–1916) German astronomer Schwarzschild was the son of a prosperous Jewish businessman from Frankfurt am Main. His interest in astronomy arose while he was at school and he had published two papers on binary orbits by the time he was 16.… … Scientists