They are a phenomenon dating back almost to the beginning of the universe, and yet, black holes are a relatively recent discovery. Their existence was first predicted in the early 1920’s as an abstraction of Einstein’s theory of General Relativity. The idea of a gravitational singularity, while obviously valid in mathematical terms, was not one anyone could conceive of in terms of any physical reality.
In 1919, when British astronomer, Sir Arthur Eddington through observational evidence of gravitational lensing-the effect of light being bent by a massive gravitational source such as starlight by the Sun- provided proof of Einstein’s theory of General Relativity, the world of astrophysics was turned on its head. The static view of Newtonian gravitational law became instantly obsolete, being replaced by Einstein’s concept of a more dynamic space-time model and gravitational warping.
In 1925, based on Einstein’s theory of Special Relativity, physicist Monsignor Georges Lamatri developed his theory of a primordial atom, an instant of time (a mathematical singularity) when energy was converted into all the observable matter in the universe today. But if energy could be converted into matter than matter could also be turned back into energy. The proof of the pudding came out of the oven on July 16, 1945, with the successful testing of the first atomic bomb. The possibility of a gravitational singularity was no longer a mathematical probability, it was now a very real physical possibility. But what would a gravitational singularity look like?
In 1967, a singularity of human thought occurred bringing together the concept of a mathematical singularity in terms of General Relativity, and the reality of astronomical observation. The occasion was the discovery of very dense stars called pulsars or neutron stars. Astrophysicists soon realized these bizarre phenomena were the remnant of supernovae events (the end of life explosion of super massive stars). In the aftermath of a supernova, without the energy force of fusion to counteract the force of gravity, the star implodes into itself. But this implosion is not instantaneous, it takes time. Just as an ice skater spins faster and faster by drawing his or her arms in towards their body, so a pulsar begins to spin rapidly as matter is drawn to its center mass.
But we can see pulsars through an optical telescope. In fact, they show up even more brightly on radio telescopes because they emit a lot of x-band (microwave) radiation lower in frequency than visible light. The pulsars high rate of spin generates a tremendous amount of centrifugal force, counteracting the force of gravity compressing the star and promoting a sense of balance or gravitational equilibrium. When pulsars became a better understood phenomenon, astronomers and physicists began to contemplate what would happen if an even larger star experienced a supernova event, one 10 to 15 times more massive than the Sun. Of course, it would spin rapidly too, but the centrifugal force generated would never be enough to offset the exponential increase in gravity. As the stars mass would be drawn into its center, the immensity of its runaway gravitational force causes matter near its center to be accelerated to the speed of light.
Ordinary matter can not travel through space at the speed of light and maintain its atomic state of organization. Taking into account Einstein’s E=mc2 equation, an increase in the rate of velocity must be accompanied either by a decrease in matter, or increase in energy. As an atom is accelerated, both occur, but the mass of the atom decreases at a far lessor rate than the increase of its energy. First, the increase in inertial velocity energy overcomes the electromagnetic force binding electrons to the nucleus of an atom. The electrons are all stripped away, long before an atom’s velocity reaches anything close to the speed of light. Since the mass of its electrons is only slight with respect to the mass of the nucleus, the resulting decrease in mass hardly offsets the increase in velocity, and thus the atoms nucleus must gain energy, a whole lot of it.
The nuclear strong force is 100 times stronger than the electromagnetic force, but when the atom’s nucleus gains sufficient velocity this bond, which holds neutrons and electrons together, is also overwhelmed by the increasing nuclear energy. The atom disintegrates, leaving only protons and neutrons, and we enter a phase of matter where only the laws of quantum mechanics can explain what’s going on. This proton/neutron plasma is a reality we can not fathom in any sense of a physical reality. Pulsars are believed to be stars which reach this stage, having a core of very dense neutron plasma (hence the name neutron stars) surrounded by a dense cloud equally jam packed with protons. Outside of this is a crust of ordinary, but very dense atomic matter, in a metallic liquid state.
In 1917, Albert Einstein had just put the finishing touches on his field equation (a little more complicated than E=mc2) to express in mathematical terms his theory of General Relativity. What he had not contemplated, and would later initially dismiss as an absurdity, is the fact, that if you concentrate enough matter into a small enough area of space-time, you end up with a gravitational singularity; where gravitational force becomes infinite and matter as we know it can not exist. At this point, even the laws of quantum mechanics cease to hold up, and human minds, while putting forth plenty of exotic theories, have yet to quantify exactly what happens; what is reality. The week force binding electrons to protons to form neutrons can no longer exist. Even the protons themselves disintegrate into quarks and quarks into even less massive particles and antiparticles. It is an annihilation of matter, a state of infinite mass and infinite energy converging and coming to a standstill at a single point of space-time; it is a black hole.
The term black hole was originally used to describe this theoretical phenomenon in 1967, because within a certain radius of the center of the gravitational singularity, the acceleration force of gravity exceeds the velocity of light. Therefore, even photons(light) can not escape from a black hole. So, if you were looking at one, all you would see is darkness. Hence the label “black holes.”
But the idea that nothing can escape from a black hole has turned out to be a misnomer. In 1975, the first objects believed to be black holes were identified by effect of gravitational lensing. Since then more and more suspect black holes have been located, and in some cases jets of intense high frequency gamma radiation have been observed extruding from them. These radiation jets occur on an axis perpendicular to the gravitational plane of the black hole’s circular rotation; essentially the north and south poles of the black hole. The reason for the radiation jets may be a gravitational weakness which allows pure energy to be ejected with tremendous force from the gravitational singularity. As a plume of this energy extrudes from the black hole, far out into space, it gives up energy as reflected in a decrease of velocity, thus gaining mass, all be it an infinitesimally small amount represented by the high energy photons or gamma particles which make up the jet.
Astrophysicists believe, by developing a better understanding of what is going on in black holes, we may find a new window of human understanding into just what happened during the big bang, and maybe even before it; before there was gravity in the universe at all. Beyond any question, gravity is the cause of black holes, but who can imagine the universe without gravity?
Albert Einstein, who’s theory of General Relativity can be identified as the critical precursor to human discovery of black holes, concluded that to try and comprehend anything beyond the physical realities of the universe was a waste of time. To borrow a line from the movie Dirty Harry, “a man has got to know his limitations,” and Albert was certainly aware of his own. But perhaps some other brilliant human specimen has already been born, or soon will be, who will go beyond Einstein’s limitations, discovering some new dimension of the universe, not just in mathematical terms, but within the confines of reality.
While “wormholes” associated with gravitational singularities, as suggested by today’s science fiction entertainment, are just that, science fiction, perhaps black holes will someday become more truly representative of port holes of human understanding. Humans then, may venture forth on universal odysseys of quintessential intellectual venture, a quest of truly Star Trekian proportion.
Reference:
http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html
