Five billion years ago, a dark, vast cloud of gas and dust stretched across hundreds of light-years of space. Inside the cloud, temperatures hovered just a few degrees above absolute zero. In one small region nestled deep within the cloud, the turbulent bulk motions of gas molecules bunched enough mass together that gravity could exert its inexorable force, causing part of the cloud to collapse. Millions of years later, gravity squeezed the densest regions of the shrinking cloud to temperatures and pressures high enough to ignite thermonuclear fires, forming thousands of newborn stars.
And 4.6 billion years after that, one of the small chunks of debris left over from the formation of one of those stars, intelligent beings emerged who could ask questions about their origin. Our Sun, our solar system, our planet, everyone we know, everything we love, everything we ever cared about ~ all of these owe their existence to a collapsing gas cloud some five billion years ago.
Our lives are intimately linked to the stars. Thermonuclear reactions deep inside the Sun provide the sustenance for life on Earth. The carbon in our cells, the oxygen we breathe, the calcium in our bones, and the iron in our blood were forged inside stars that expired billions of years ago. So, you see that virtually everything is made from star dust, we are star dust.
Black holes are bodies so massive and dense that their theoretical escape velocity is greater than the speed of light itself, due to the exceptionally strong gravitational field. This means that not even light can escape from such bodies, effectively rendering them invisible ~ hence the name.
At one time black holes were entirely theoretical. The black hole theory began in 1783 when Rev. John Michell used Newtons theory of gravity to predict the possibility of "dark stars". In 1915, Einsteins General Theory of Relativity predicted so-called "Schwartzschild singularities" (non-rotating black holes). And in 1963 the "Kerr" or rotating black hole solution was found. This was especially important, since most stars are rotating, and the rotation rate is expected to increase when such stars collapse. They were renamed "black holes" in 1967. Today their existence has been confirmed, both in our own galaxy and elsewhere in the universe, bringing the total known to 33 (the closest being at the center of the Andromeda galaxy, and the largest at the center of galaxy M106). We can infer the presence and location of a black hole by monitoring the gravitational effects that it has on surrounding objects like companion stars. They are also evidenced by the emission of x-rays, which are easily detectable.
A black hole is formed when a very large star (at least 30 times the mass of our Sun) dies or runs out of hydrogen, and collapses or implodes under its own weight. It shrinks down to an infinitely dense point known as a singularity (the point at which the stars mass is centered), and it is at this point that conventional mathematics can no longer cope. Around the singularity, at the opening of the black hole, there is a doughnut-shaped ring called the event horizon. It is the black holes gravitational boundary beyond which nothing, including light, can escape. And once this boundary is crossed, there is no return. Einstein has proven that gravity can not only capture light, but can also distort time and space. Inside the event horizon, the entire concept of time and space completely breaks down.
Black holes have a reputation for sucking in everything around them. Thankfully, the black holes we know about are of no danger to Earth. The closest stellar-sized black hole, V404 Cygni, is at least 15 light years away, and super massive black holes are confined to the centers of distant galaxies, so they pose no conceivable threat. Black holes are no more deadly than any other objects of the same mass ~ if you keep your distance. A black hole could suck in only enough material to equal its own mass, and no more.
There are other implications of other phenomena concerning black holes. Einsteins equations suggest that black holes theoretically should lead to parallel universes; i.e., one that is separate from our own. There may be multiple universes, each slightly different to the one we are presently existing in. There is also the possibly of time travel into the past and future. And the possibility of using a wormhole (where two black holes connect), to travel instantly to far places within the universe.
If you were standing on the edge of the event horizon and you fell feet first into a black hole, the difference between the gravitational pull on your head and your feet would be so powerful that it would instantly stretch you out like spaghetti. If you could look back as you fell, you would see the future history of the universe flash before your eyes. But once inside the event horizon, you would be unable to communicate anything you saw back to anyone outside it. As you neared the singularity at the center, you would have felt yourself being torn apart, atom by atom. Space and time would be so distorted at this point, everything we have ever known about the universe has broken down. Some say at this point, only a primordial froth exists.
Black holes could actually be beneficial. Mathematician Roger Penrose of Oxford University has calculated that a technologically advanced civilization could extract enough energy from a black hole to supply all of its power requirements.
Penroses idea requires the civilization to build a structure encircling the black hole, from which a stream of fuel can be "fed" into it. At the event horizon, each particle in the fuel stream is then split into two fragments ~ perhaps using suitably placed explosive charges. Penrose has calculated that at the very moment one of these fragments falls over the black holes event horizon, the other fragment will throw out a kick of pure energy supplied by the annihilation of its partner. This is something like the boost you get after jumping from a carousel.
The theory goes on to suggest that the "energy kicks" could be collected by the structure around the black hole, but energy extracted in this way would not be limitless. Calculations by Demetrios Christodoulou, a researcher at Princeton University, New Jersey, show that a black holes rate of spin is steadily reduced by the Penrose process. There would come a point when the black hole stops spinning, and its energy-producing properties would vanish.
If the same civilization could build a craft capable of withstanding the enormous forces that apply in and around a black hole, scientists have speculated that it might be possible to cross the event horizon into a new region of space-time, through what is known as a wormhole. So living next to a black hole could not only save on utilities, it could also provide the ultimate ticket to the rest of the universe ~ past, present and future.
- David D. Chittenden III
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