Black hole
Simulated view of a black hole
(center) in front of the Large Magellanic Cloud.
Note the gravitational lensing effect, which produces
two enlarged but highly distorted views of the Cloud. Across the top, the Milky Way
disk appears distorted into an arc.
A black hole is a region of spacetime
from which nothing, not even light, can escape.[1]
The theory of general relativity predicts that a sufficiently
compact mass
will deform spacetime to form a black hole. Around a black hole there is a
mathematically defined surface called an event horizon
that marks the point of no return. It is called "black" because it
absorbs all the light that hits the horizon, reflecting nothing, just like a
perfect black body
in thermodynamics.[2]
Quantum mechanics predicts that black
holes emit radiation like a black body with a finite temperature.
This temperature is inversely proportional to the mass of the black hole,
making it difficult to observe this radiation for black holes of stellar mass or greater.
Objects whose gravity field
is too strong for light to escape were first considered in the 18th century by John Michell
and Pierre-Simon Laplace. The first modern solution
of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its
interpretation as a region of space from which nothing can escape was not fully
appreciated for another four decades. Long considered a mathematical curiosity,
it was during the 1960s that theoretical work showed black holes were a generic
prediction of general relativity. The discovery of neutron stars
sparked interest in gravitationally collapsed compact objects
as a possible astrophysical reality.
Black holes of stellar mass are
expected to form when very massive stars collapse at the end of their life
cycle. After a black hole has formed it can continue to grow by absorbing mass
from its surroundings. By absorbing other stars and merging with other black
holes, supermassive black holes of millions of
solar masses may form. There is general consensus that supermassive black holes
exist in the centers of most galaxies. In particular, there is strong evidence of a black
hole of more than 4 million solar masses
at the center of our galaxy, the Milky Way.
Despite its invisible interior, the
presence of a black hole can be inferred through its interaction with other matter and with
light
and other electromagnetic radiation. From stellar
movement, the mass and location of an invisible companion object can be
calculated; in a number of cases the only known object capable of meeting these
criteria is a black hole. Astronomers have identified numerous stellar black
hole candidates in binary systems by studying the movement of
their companion stars in this way.