Ship's Log A Short History of Black Holes Discoveries

John Michell of Cambridge first suggested the concept of a black hole as early as 1783. Michell discussed the possibility of a star with a gravitational force so strong that not even light could escape it, thus preventing astronomers from observing such phenomena. French scientist Marquis de Laplace mentioned the possibility of such stars in the first few editions of his book The System of the World, although failed to in later editions because the idea of a star with a gravitational force that could overpower light did not comply with the wave theory of light, which was generally accepted at the time.* This theory seemed to suggest that light could not be affected by gravity, a concept that is key to the theories of Michell and Laplace.

A short time after Einstein published his general theory of relativity in 1915, a German physicist name Karl Schwarzchild wrote a paper describing a structure called a singularity. Drawing from Einstein's theory, Schwarzchild contended that a matter could theoretically be drawn into a point with virtually no volume and an infinite density. He called this object a point mass, later dubbed a singularity. In addition, Schwarzchild determined that there is a definite boundary around a singularity called the event horizon.

In 1928, through his research on white dwarfs, graduate student Subrahmanyan Chandrasekhar hypothesized that a dying star of a certain mass might form a point with enough gravitational pull to trap light.

Object with Companion (near-infrared image)

Stars thrive on the supply of hydrogen gas of which they are made up. When the hydrogen gas runs out, the star begins to contract. Chandrasekhar contended that stars are able to maintain themselves after using up their fuel because their gas particles move away from each other as the star contracts, which balances out the star's gravitational pull.** Chandrasekhar hypothesized that a star of a certain mass is not able to achieve this balance because its gravity is too great to overcome. This particular mass is known as Chandrasekhar's limit. After they have stopped contracting, stars with a mass under Chandrasekhar's limit reach a final state called a white dwarf, or in certain cases form a structure called a neutron star. Stars with masses above this limit would contract to a point of infinite density. At Chandrasekhar's time, however, the validity of such an idea was under serious debate and as a result was not widely accepted.

In 1939, American physicist Robert Opppenheimer developed a possible explanation for the nature of these points of infinite density. Oppenheimer theorized that the gravitational pull of a star with infinite density would cause light rays to devitate from their path and bend towards the star. Eventually, the gravity of the star would become so great that the light would become trapped by it and would be unable to escape, preventing one from observing it. At this point the star is a black hole.*** Along with graduate student Hartland S. Snyder, Oppenheimer developed equations demonstrating the possibility of a star collapsing in upon itself and forming a black hole.

In the 1960s and 70s, the scientific community was awash in new speculation about the nature of the universe, including black holes. In 1963, Oppenheimer and Fred Hoyle of Britain published a new set of speculations about singularities. Between 1965 and 1970, Stephen Hawking and Roger Penrose of Cambridge conducted studies that lead them to conclude that according to the general theory of relativity there must be a singularity within a black hole in which time and the laws of science at this singularity no longer exist. In 1971, Hawking introduced the idea of primordial, or mini black holes formed almost immediately after the Big Bang. Hawking furthered postulated that black holes could release particles and gradually erode over time, thus refuting the belief that nothing could escape from a black hole. This idea presented the possibility of detecting black holes through the emission of gamma radiation (see Detection). Other scientists hypothesized that black holes were openings in the fabric of space-time, so particles entering a black hole might be transported to another part of the universe. These tunnels were dubbed wormholes, and although their existence is uncertain, they have been present in science fiction ever since (see Science Fiction). Additional hypotheses have been introduced concerning rotating vs. non-rotating black holes and other aspects of these mysterious phenomena as well.

*Scientists have come to realize that light behaves both a wave and a particle, causing it to display properties of both. During the eighteenth century, however, there were two separate theories explaining the nature of light as a wave and a particle, respectively, causing heated debate over which theory was accurate.
**According to the Pauli Exclusion Principle, particles of matter cannot occupy the same. position and have the same velocity. Therefore, when gas particles in a star begin to contract, they move away from each other because they must have different velocities, being so close together.
***American scientist John Wheeler coined the term "black hole" in 1969.