Brief History of Black Holes!


  • 1915--- Schwarzschild and Droste independently discover a solution to Einstein's field equations for gravity, for a point particle.
• 1931 - 39--- Chandrasekhar, Oppenheimer, Tolman and Volkoff realize that if a star has a mass above a certain limit, there is no relativistic Fermi pressure based on any fundamental force of nature that can halt gravitational collapse. [This mass limit is currently computed to be about 2.2 solar masses. The lowest-mass black holes observed to date have a mass of about 3 solar masses.]  For stars at or above some mass limit, and which do not undergo huge mass losses at end-stage stellar evolution, eventual collapse to a singularity seems inevitable.  The Schwarzschild surface,  a confusing feature of Schwarzchild's solution, they eventually realized, is a boundary (surrounding the singularity), usually called the event horizon, which an infalling object, as seen by an external observer, will take an infinite time to reach.  However, in the co-moving frame of the object, the surface is crossed in a finite time. Once past the surface, all traversable paths intersect the singularity at the center. 

• 1958 - 1974--- A large number of talented theoretical physicists start working in the area of Einstein's theory of gravity. New analytic solutions are discovered for point particles, and  pioneering work on numerical methods begins.   [It also became clear that the singularity was a real, unavoidable feature of the classical field theory. Approximately one out of every thousand stars is massive enough to become a black hole. The term “black hole” was first used in the early 1960s, but did not become popular until John Archibald Wheeler started using it in early 1968.]

All black holes MUST rotate.
Rotating black hole



Since black holes that are end-products of stellar evolution must be rotating, and very massive black holes that result from mergers of smaller black holes must also be rotating, and supermassive black holes that form in the Dark Ages from enormously dense clouds of gas and dust must be rotating, it is clear that all black holes rotate. The analytic solution for a rotating black hole is the Kerr solution, discovered here at UT in 1963 by Roy Kerr. The singularity is a ring of finite radius but zero thickness, possessing mass and angular momentum.   A characteristic of Einstein's theory of gravity is that any object near a rotating mass has a torque exerted on it, the so-called “frame-dragging” effect.  All boundaries for a rotating black hole exist in two forms, one for objects with total angular momentum projection parallel to the black hole's angular momentum, and the other for objects with total angular momentum projection antiparallel to the black hole's angular momentum.  Thus there are two Event Horizons, and two Photon Spheres, regions where photons can go into (complex) orbits.  There are also two Ergosphere boundaries,  between which, no matter what the initial velocity of the object, it is dragged along with the black hole's rotation.  In other words, within the Ergosphere, it is impossible for an object to be at rest.  The inner boundary of the Ergosphere is the outer Event Horizon.  Contrary to the diagram above, the Event Horizons are oblate spheroids, and the Ergosphere region is overall shaped something like a pumpkin. So incredibly difficult is the mathematics of Einstein's theory of gravity that it is only in the summer of 2022 that it has finally been possible to prove that the solution for a slowly-rotating black hole is stable against perturbations!

In a strong gravitational field, space is highly non-Euclidian, and closed orbits are not possible (the force does not go like the inverse square of the distance).

Stars orbiting the supermassive black hole, Sagittarus A* at the center of our own galaxy.  Predicted by John Michell (1724 – 1793)! This black hole is unfortunately difficult to image, because a direct line of sight to it passes through the densest part of our galaxy.  It was successfully imaged in mid-2022.


Relativistic jets are a feature of many exotic astronomical objects. Black holes themselves do not have magnetic poles or magnetic fields. So it remains somewhat of a mystery as to what provides the spinning magnetic fields that propel energetic and enormous polar jets out perpendicular to an accretion disk, as seen with some black holes at galactic centers, but not others.

Since most black holes at galactic centers do not have relativistic jets, astronomers assume that in active galaxies, the accretion disk of the central black hole must be surrounded by a “torus,” an enormous structure like a natural Tokomak, which stores ultra-relativistic particles and magnetic field lines, and injects them into the accretion disk at a steady rate! As more black holes become available for study, with considerable intensity variation in the jets produced, the jet mechanism is becoming clearer. Roughly one in 10 black holes have these jets.

Sir Roger Penrose (1931 - ) revolutionized the mathematical approach to solution of the equations of Einstein's Theory of Gravity, and emphasized that formation of black holes is an essentially unavoidable product of stellar evolution. He shared the Nobel Prize in Physics for 2020, for this work.

In a 1937 science fiction novel by British writer Olaf Stapledon, STARMAKER, which provides a panoramic history of all intelligent life in the universe, early galaxies are depicted as intelligent beings, who battle one another by sending out enormous jets of relativistic particles, to cut one another in two! At the time Stapledon wrote, little or nothing was known about galaxies, and no galactic jets had ever been observed.

In 1979 Disney Studios released a live-action science fantasy movie called THE BLACK HOLE. At the end of the film (based loosely on Melville's MOBY DICK, with the Black Hole taking the role of Moby Dick) it was revealed that a black hole is a portal to hell itself!


Black Hole Primer

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