Results of computer simulation of stars and gas orbiting a black hole at the center of the Milky Way.
credit: ESO/MPE/Marc Schartmann
image source: http://www.eso.org/public/images/eso1151a
For many of us, the subject of black holes and their properties is a mysterious conglomeration of fanciful fact and magic. In loosely paraphrasing the author, Arthur C. Clarke—I mean the science of black holes is like magic for most of us —the subject is as indistinguishable as the practice of religion from the magic of Harry Houdini. In short, we may never stumble upon one during our entire life.
Einstein never completely accepted the notion of black holes in General Relativity—however the first solution to his “relativistic field equations” suggested their existence. This solution was published in 1916; the author (Karl Schwarzschild) suggested the existence of a singularity—or in modern parlance, a point mass. Schwarzschild’s solution, in relativistic dynamics, is known by the term: static singularity. Furthermore, Schwarzschild’s static singularity is the simplest, theoretical black hole; in fact, it may even be the simplest way to understand some of the more complex notions of the Universe. The term black hole has its origins in classical mechanics, when it was suggested separately by Pierre-Simon Laplace and John Michell (both in the 18th century) that there may exist bodies, like stars, whose gravity did not allow light to escape from the surface. However, black holes are small compact objects with masses that may be many hundreds of times that of the Sun—but of course the object is dark. Because of their extreme mass, black holes are said to distort the “space surrounding them,” they act as powerful sources of gravitational attraction. Black holes, also, radiate X-Rays when objects fall into them—and it is said that object’s “information is lost forever.” However, Dr. Stephen Hawking, through his pioneering work in 1970s, discovered that black holes can radiate “heat.” This radiation is known as “Hawking-Unruh radiation.”
The discovery of the first black hole seems to be all but physically confirmed; it was discovered by Riccardo Giaconni and his group in the early 1970s, when he utilized data from an X-Ray satellite, Uhuru. Approximately a decade prior to Giaconni’s discovery, NASA satellites had detected strong X-Ray sources emanating different points in the sky. Giaconni proposed the launch of an “orbiting observatory” for the express purpose of searching for X-Ray sources. Uhuru was launched in 1970; and by 1978, there were more than 300 X-Ray sources. Many of these sources are black hole candidates or, as in the case of Cyg X-1; the first confirmed black hole candidate. Giaconni was awarded a Nobel in 2002 for his initial use of an X-Ray observatory to break open the field of X-Ray astronomy.