The concept of a star from which nothing can escape, not even light, was first speculated by the world of science in November 1783, when Rev John Michell (b. 1720s, probably in Nottingham), the Rector of Thornhill in Yorkshire, read a paper to the Royal Society. In it he wrote, "If the semi-diameter of a sphere of the same density of the Sun were to exceed that of the Sun in the proportion of five hundred to one, and by supposing light to be attracted by the same force in proportion to its [mass] with other bodies, all light emitted from such a body would be made to return towards it, by its own proper gravity." This black hole paper, too far ahead of its time, was not re-discovered until the 1970s.
Before then, credit for the concept of black holes had generally been given to the French astronomer Pierre Simon de LaPlace (b. 23 March 1749, Beaumont-en-Auge, Normandy; d. 5 March 1827, Paris). In the first edition only of his Systeme du Monde (1796), he similarly deduced their hypothetical presence from an application of Newtonian physics such as the escape velocity of an object. Newton followed Galileos lead in stating that gravity, while being proportional in strength to the mass of its source, produces the same motion in all other bodies, regardless of their nature or mass.
It took the boggling ideas of the Swiss Albert Einstein (b. 14 March 1879, 1130 LMT, Ulm, Bavaria; d. 18 April 1955, Princeton NJ) to develop the implications of the basic idea, linking space, time and light. His theory of Special Relativity was published in Annalen der Physik in 1905 and the theory of General Relativity followed ten years later, incorporating his work on gravity. It proposed in essence that gravity could warp space and slow time in proportion to the greatness of its gravitational field. Paraphrased later, it argued "matter curves space-time; space-time moves matter."
He took the speed of light to be the one constant, and the absolute maximum speed of any physical phenomenon. From Einsteins papers, a German astronomer called Karl Schwarzschild, fighting on the Russian front, made further calculations in 1916 which predicted the existence of collapsed stellar bodies that emit no radiation, determining the gravitational radius of a black hole, numerically identical to John Michells speculation. Schwarzchild died in May that year of a skin disease contracted in the war zone. John Archibald Wheeler, a leading exponent of the black hole concept, coined the term "black hole" in 1967.
Subrahmanyan Chandrasekhar (b. 19 October 1910, Lahore; d. 21 August 1995, Chicago IL) was the first to calculate that if a star 1.5 times in mass that of our Sun was to run out of fuel, it would collapse into an infinitely dense single point under its own gravity. Albert Einstein, whose work had made the concept possible, and Arthur Eddington, a founding father of astro-physics, both disputed this concept, though it is now believed to be substantially correct.
A black hole can be formed from the death of a massive star, which must have approximately three times the mass of our Sun or more. After it has exhausted its internal thermonuclear fuels it becomes unstable and collapses inwardly upon itself. While its gravitational field remains unchanged, its volume becomes compressed to zero, and its density to infinity. This point is known as the singularity, and is the centre of a black hole, hidden by a surrounding black void. The binding forces holding the subatomic particles or quarks together become overwhelmed and the ex-star becomes the ultimate source of fundamental matter and energy. When photographed, the surrounding area appears pink, thought to be the result of gas emissions from the mangled remnants of space matter, gas clouds and churned-up stars, as they hurl towards the black hole.
Anyone foolhardy enough to approach a black hole would see a characteristic black disc, surrounded by a thin glowing pink halo. This is caused by the lens-like effect of the black holes intense gravity on the light of the stars and galaxies that lie behind it. If they were actually to cross the Rubicon the gravitational gradient from the hole would increase so rapidly that it would become so much more powerful at their feet than their head that their body would become spaghettified - instantly stretched and then rather unpleasantly pulled apart.
The surface of the black hole object is called the event horizon. Inside the object, the velocity required for matter to escape its own gravitational field, or escape velocity, is greater than the speed of light, so that not even rays of light can emerge. If another star collides with the black hole, or the dying star becoming a black hole, it too will collapse to zero volume, and add to the gravitational pull of the black hole. Consequently the redoubled black hole will gradually swallow up other stars that fall within its gravitational field, and some will become a super-massive black hole. A doomed star will spiral gradually and inexorably towards the black hole. As it is consumed by the black hole, the interior atmosphere of the black hole reaches millions of degrees in temperature and generates X-rays from all the particles in its region. These X-rays are detectable and are occasionally eclipsed by a star that is in the process of falling into the black hole, and this how they are located. At this time the group is known as an eclipsing X-ray binary system, and has a definable orbital period.
Super-massive black holes contribute as much energy to the Universe as all the stars combined. It is now known that at least 15 per cent of them are relatively recent, being less than half the age of the Universe. At any one time about 10 per cent of all super-massive black holes will be pulling in vast quantities of gas, as well as whole stars, and are thus still growing, ever slowly evolving, over periods of more than a billion years.
When neutron star pairs collapse into each other and form black holes, copious amounts of gravitational waves of energy are released from them, making the area around the black hole intensely bright. This is equivalent to the complete destruction of up to 42% of the mass involved, as a tightly focused beam of cosmic rays, capable of travelling a million light years at full power. This makes black holes among the most powerful energy sources in the Universe. If this ray encounters any starlight, it forces the light to accelerate and travel in front of it, pumping its photons energy levels up to become gamma rays. During this process, the black hole is described as a feeding black hole.
A feeding black hole will push all surrounding gases and galaxies away in its giant wind, until they are all so far away that they becomes invisible. Stars on the border of its area of influence are harder to push away the more slow-moving they are. The speed at which stars encircle in the outer reach of its galaxy is known as its sigma. The bigger that the black hole is, the faster the speed of stars at the edge of the galaxy will be.
Eventually, the moment will arrive when this feeding process is complete and the super-massive black holes domain will become totally empty. It will then stop feeding and become invisible, dark and silent.
Super-massive black holes can be seen to play a part in galaxy formation. In this cycle, early gas clouds collapse to form a giant black hole, which feeds on gas. This creates a quasar, causing temperature changes. The gases condense into stars, triggering the birth of a new galaxy.
Interestingly, there are reports that our super-massive black hole, the one at the centre of the Milky Way, 24,000 light years away from Earth, has begun to feed again.
Astronomers detect gamma ray bursts in distant galaxies about once a day. It is thought that it is 251 million years since the last time cosmic rays struck Earth, when they wiped out 95% of animal life, and caused the remaining 5% to mutate. When they enter the atmosphere, cosmic ray jets shower muons, lethal high-energy subatomic particles, onto the Earths surface. These will penetrate hundreds of metres underground and underwater, for up to a month, spread around the globe by the Earths rotation and by radiation borne on atmospheric winds. These muon showers contain on average 50 times the ionising radiation dose necessary to kill all animal life on Earth. There have been five such mass extinctions in the past 500 million years, suggesting we are 100 million years overdue for the next (the most recent mass extinction, 64 million years ago, is attributed to a meteorite impact). However, cosmic rays have also played a part in our evolution, since cells evolve through mutations in their DNA genetic material, and these rays must have been a driving force in this over 4.5 billion years.
A black hole with a mass at its centre ten times that of the Sun would have a radius (to its event horizon) of 18.4 miles. At the black hole, time has stopped; indeed within the black hole time will travel backwards, creating negative time. Black holes could lead to a fifth dimension.
Some astronomers have speculated that black holes could be formed not only from stars but also from large volumes of interstellar gas, collapsing under intense gravitational force into super-massive black holes. If so the enormous energy output of some galactic systems and quasars could be explained. This idea remained only a theory until 1994, when information from the Hubble Space Telescope disclosed the presence of a super-massive black hole at the centre of the M87 galaxy, the size of our solar system, but with a mass of up to 3 billion Suns.
Galaxy NGC4258 appears to have at its centre a massive object 10,000 times denser than any known star cluster, which is thought to be a black hole. It is thought that massive black holes may exist at the centre of all globular clusters of stars, since these seem to generate X-ray pulses. Research of X-ray emissions from stars can be dated from 12 December 1970, when the Uhuru ("Freedom" in Swahili, as Trekkies will know) satellite was launched from the Kenyan coast to collect X-ray source data.
In 1998, a cluster of 100 or so massive stars was found in the Arches, near the centre of our galaxy. Several were among the most massive in the universe, averaging twenty times the mass of the Sun. Powerful synchotron radiation emanates from the Galactic Centre, in the form of X-rays and gamma rays. It now seems virtually certain that a 3 million solar-mass black hole exists there. Andrea Ghez from UCLA has precisely located it, using the Keck Observatory in Hawaii. Furthermore, there is new evidence, substantiated by a Hubble search that a super-massive black hole exists at the centre of every galaxy.
In the year 2000, doomed stars spiraling towards the perimeter of the Galactic Centre event horizon were first observed. The nearest to the Galactic Centre has an approximately 15-year orbit. Pluto will be approaching the Galactic Centre by the year 2005 (from a safe distance).
In September 2001 a violent, rapid X-ray flare was captured by NASA's Chandra X-ray Observatory, originating from the direction of the super-massive black hole at the centre of our Milky Way Galaxy. Light intensity in the vicinity of Sagittarius A increased to 45 times its previous level within ten minutes, then dropping back, only to restore the more intense energy, returning to normal after a period of about three hours. The flare was detected by Fredrick K Baganoff of the Massachusetts Institute of Technology (MIT) in Cambridge MA. The data provided the best evidence yet of the area just outside this event horizon, as close to the black hole as the Earth is to the Sun. It occurred as Mars was crossing the Galactic Centre, as viewed from Earth.
“This is extremely exciting because it's the first time we have seen our own neighbourhood super-massive black hole devour a chunk of material. It's as if the material there sent us a postcard before it fell in,” said Fredrick Baganoff. “The rapid rise and fall of the X-rays from this outburst are compelling evidence that the X-ray emission is coming from matter falling into a super-massive black hole, confirming that it is powered by the same accretion process as quasars and other active galactic nuclei.”
“Simply, 'Give me more mass and I'll make more energy,' this point bellows,” says Phillip Sedgwick, “Mass symbolically represents matter - as in what matters. Energy, especially in the X-Ray spectrum, perceives the light of the real issue.”
The first type of black hole to be deduced, in 1916, was the Schwarzchild Black Hole, which has mass only and is spherically symmetrical. Outside the event horizon of the black hole, disorganised random patches of light swirl in a photon sphere, and all objects in space near to this photon sphere are pulled through it and into the event horizon, where they reach the singularity to be crushed into nothingness by infinite pressure.
Three other types of black hole have been speculated and subsequently found to exist. The Reissner-Nordstrum Black Hole has both mass and charge, and was hypothesised between 1916 and 1918. The Spinning Black Hole, or Kerr Black Hole solution, named after Roy Kerr, was published in 1963, and consisted of a rotating black hole with mass and angular momentum which was axially symmetrical. The Kerr-Newman Black Hole (1965) is more complex, having mass, charge and angular momentum.
The Kruskal-Szekeres diagram model (1960) describes a black hole that has two event horizons, and two separate universe systems outside it. This has bred the concept of two black holes vastly distant from each other, perhaps existing in different dimensions, but connected by a space-time tunnel called a wormhole. This in turn introduces the possibility of both positive and negative time, and of past and future light; therefore, also the possibilities of time/space travel to other realities.
If there are black holes then scientists suppose there may also be grey holes and white holes. This is because black holes repulse the matter they attract at singularity, albeit temporarily. Matter can consequently be extruded into our Universe for a finite period as an observable grey hole, before being sucked back by the black hole gravity. A white hole hypothetically exists on the other side of the black hole, connected by a one-way wormhole, to form a linked pair in alternate realities of space, consisting of particles and anti-particles. The white hole would be the precise opposite of a black hole, acting as a perfect emitter or "cosmic gusher". It would pop into place in space as a singularity and gradually acquire mass and size, and release light.
Black holes also demonstrate that time travel must theoretically be possible. In 1963, on the eve of the first Dr Who programme, Dr Roy Kerr published a paper using the theory of relativity as applied to black holes to speculate on the idea of a time machine. If a space craft was able to skim the edge of the gravitational well of a black hole without being sucked in, time would travel far more slowly for its occupants. When they then travelled to any point beyond the black hole, as outside events would have been proceeding at their normal rate, they would be in the distant future.
In Frank Tiplers extension of this concept in 1974, a special type of black hole called a naked singularity is produced (presumably by a Star Trek-type deeply advanced space-travelling species) which is rotating. This rotation has the effect of twisting local space-time (the fourth dimension) to the degree that time itself becomes another dimension through which a spacecraft could be piloted.
In theory, two or more black holes could collide, causing the most cataclysmic event conceivable in the known Universe. If this were to happen within 700,000,000 light years from Earth, a distance incorporating thousands of star systems, since 1999 it would have been possible to detect the event using the Laser Interferometer Gravitational Wave Observatory (LIGO). Sited near Baton Rouge LA, this can pick up the gravity waves such events will produce, as Einsteins general theory of relativity has shown.
A string theory black hole is a black hole spacetime that satisfies the conditions needed for a sensible quantum string theory to exist in that spacetime. These stringy black hole spacetimes are related to other stringy spacetimes through duality symmetries. These symmetries tell us that the five separately evolved superstring theories so far developed could each be related to one of the others, or in fact be the same theory, expressed in different ways.
Ulf Leonhardt, professor of theoretical physics at St Andrews University, Scotland, plans to make a raindrop-sized black hole in a lab before 2005, created by a whirlpool of atoms.
Even a black hole is not indestructible, though its life span can greatly exceed the current age of our present universe. Stephen Hawking (b. 8 January 1942, St Albans) has shown, by using the laws of thermodynamics in parallel with those governing black hole matters, and with due regard to quantum phenomena, that a black hole has a finite temperature and must radiate energy and particles. Its temperature is inversely proportional to its mass; the lower its mass, the higher its temperature and the faster the rate at which a black hole loses mass. Therefore, black holes have temperature and entropy and can decay by quantum processes. As the entropy of a black hole is one quarter of the area of the event horizon, the entropy reduces as the black hole decays, and the event horizon area becomes increasingly smaller. So according to Hawking, a black hole will eventually evaporate in a detonation of gamma rays and energy particles.
Then again, in a trillion years the Universe itself will start to die. All the large stars will have become black holes or neutron stars, and no new stars will form. The sky will look empty and black. By 100 trillion AD, even the most super-massive black hole will have exhausted all its fuel and died. Perhaps another Big Bang will start the whole process over again, or perhaps any surviving intelligent life will flee into hyperspace, or a fourth dimension, or parallel multiverse. Perhaps they were already surfing in curved space at infinity, where all time and space simultaneously exists.
Astrologers who have looked into the phenomenon see the black hole as the sci-fi equivalent of the Hades of myth. It is considered by writers such as Phillip Sedgwick that the energy from the X-rays emitting from the black hole may stimulate our super conscious minds. This is the area of the mind attributed to the crown chakra and higher energy vibrations.
The natal black hole may trigger our capacities for developing the extra powers of consciousness we possess, if we let it, or it may do nothing at all, depending on our responses to its stimulation. During periods of X-ray eclipse, a few hours at a time, we are cut off from its influence, and during this time we may feel extremely alienated, disconnected and lacking in awareness and function. This may lead to a period of self-defeating and negatively reactive behaviour until the next half-cycle brings about the re-constructive abilities needed.