This post is going to be rather wordy, and probably dreadfully dull, so those of you without true grit may want to turn back now. For you, the intrepid adventurer into the cosmos, I must warn that we will be discussing such thrilling topics as stellar evolution, subatomic physics, Newtonian gravitational physics, General Relativity, and the final destiny of the Universe. If this fails to send you fleeing from your computer in a panic, you may proceed-but at your own peril! Don`t say I didn`t warn you.
Our topic today will be black holes. No, I`m not speaking of the yawning chasm between Jesse Jackson`s jaws, nor the place my taxdollars go, nor even Ted Kennedy`s liver or the region enclosed by Cindy Sheehan`s cranium. I`m speaking about collapsed stars (and I don`t mean Madonna!)
I thought this might be a good time to explain this, since I`ve been discussing black holes in relations to Entropy, and many of you, my learned readers, may be a bit hazy on the whole concept.
To begin this discussion, let me first explain the classifications of stars. There are, essentially, two groupings of stars-main sequence and non-main sequence. Main sequence stars have been carefully catalogued
based on their temperature, and if an astronomer determines this (by studying the stellar spectrum) he can determine the absolute magnitude (real brightness, or luminosity) of a star and where it will fit into an exact pidgeonhole on the main sequence. Astronomers catalogue this using the Hertzsprung-Russel diagram, which places a star where it ought to be. Stars of the same class will display similar spectrum when analyzed, and this allows the astronomer to determine a great deal about the star-such as where it is and how it is moving relative the the Earth. If the star is classified as a G2, for instance, the shifting of the spectrum will tell if the star is moving towards or away from us, and at what rate. The classifications of main sequence stars is a vital part of astronomy.
Now, the main sequence stars are classed as follows: M,K,G,F,A,B, and O. (They are also classed by a number to denote temperature-e.g. G2 for the Sun.) The M class stars are the red dwarfs, and 9 out of every 10 stars in the galaxy are M. These are also the oldest, many of which date back to the beginning of the galaxy, and, thanks to their niggardly output of energy, will outlast most other stars. Proxima Centari (the closest star to Earth) and Bernard`s star are two examples of M class stars.
K class stars are yellow-orange stars, generally smaller and cooler than our sun. 61 Signi A and B are examples of this type, as is Alpha Centari B.
Our own sun is a G2 star, a yellow dwarf. Alpha Centari A is likewise G2, although it is slightly larger than Sol. Tau Ceti is a G0 star.
F stars are yellow white. An example is Fomalhaut or Procyon.
A`s are Blue white-eg. Sirius.
B`s are the blue Supergiants, such as Rigel, and O`s radiate mostly in ultraviolet becaus they are unbelievably hot.
Now many of these stars will eventually move off of the main sequence to become non-main sequence stars. Stars similar to our sun generally swell and cool, eventually expanding their wastelines worse than Sally Struthers and becoming Red Giants. Red Giants are generally M class stars, and are the largest in size of all known stars. (Betelguese and Aldebaran are examples of Red Giants.) Many of these great gas bags would swallow much of the solar system, if they were to replace our sun. In fact, the Sun will someday become such a star, and will probably swell to the orbit of Mars.
Red Giants remind me of Howard Dean; red, dull, and full of hot air.
After a red giant exhausts its fuel, it collapses into a white dwarf. A white dwarf is generally an A class star, fairly hot and rich in ultraviolets. There is no longer any fusion process occuring in a white dwarf, and the radiation coming from such a star is the result of pressure and friction caused as the body contracts. Most white dwarfs last only about a million years.
There are a number of other non-main sequence stars, which do not particulary concern us here.
Now, this process of expansion holds for many stars comparable to our sun, and is a normal event in our Universe. But what about larger stars?
At 1.4 times the mass of the sun a strange thing can occur. Indian Scientist Subrahmanyan Chandrasekhar
worked out that any star above this mass limit will Supernova (explode) rather than collapse into a white dwarf after it has exhausted its nuclear fuel. That is, most stars above this limit will supernova. There are exceptions.
Sometimes, a star will refuse to blow, and will lose internal pressure. A star above Chandrasekhar`s Limit cannot become a white dwarf-it is simply too massive. It shrinks and shrinks, and eventually undergoes a frightening metamorphosis; it becomes a neutron star.
When the pulsars were first discovered, scientists thought that aliens were sending signals to them! They flashed radio waves with regular frequency, and appeared to be beacons of some kind. Eventually, it was discovered that they were rotating neutron stars.
Now, the matter we normally encounter is composed of protons (and neutrons) in the nucleus with electrons orbiting. These electrons generally maintain the same orbit (basic state) unless the atom is pumped with energy, in which case the electrons move into higher, set orbits (which are numbered) where they remain until the atom can spit out a photon of energy and the electron can return to the lowest orbit. (This fact laid the groundwork for quantum physics, by the way.) Now, inside of a star, matter is squashed together so tightly that the electrons are no longer able to maintain basic state. In fact, by being forced into the same space, the electrons cease to function as independent particles but become a kind of gas while remaining outside of the nucleus. This is called Degenerate Matter
, and exists inside of many stars.
But this process can go further, and the electrons can be forced inside
the protons in the nucleus of the atom. When this happens, the positive electical charge of the proton is canceled out by the negative charge of the electron, and the particle becomes a neutron.
A neutron star forms when a star with a mass higher than 1.4 solar masses fails to supernova, and collapses into a sphere generally about 10 miles in diameter. For two weeks during the collapse the dying star radiates x-rays, and then cools down. Often the collapse is accompanied by an acceleration of rotation, so a neutron star can rotate very rapidly (often a number of times per MINUTE). A hot spot on the surface of this strange star allows the body to release pent-up energy, and this causes the radio effect we witness with a pulsar. A neutron star is composed of pure neutronium-neutrons held by together by gravity and pressure. It is the densest matter in the Universe.
But what about the really
big stars? At 5 solar masses, a very disturbing thing can occur; the star passes through the neutron star stage and continues to collapse. Eventually, it reaches a point where it disappears...
Isaac Newton described the behavior of the force of Gravity with his equation g=G x m1xm2/d. (It`s hard to write equations on the keyboard!) This means that (g)gravitational attraction equals the (G) the gravitational constant times the (m1xm2)mass of the two bodies in question multiplied together and divided by (d) the distance between their centers
. What this means is that, as a massive body contracts, its total gravitational influence remains the same, but the gravitational attraction at the surface of the body increases. A neutron star is no more massive than the star from which it formed, but the gravitational attraction at its surface is enormous, since the center of the star is only about 5 miles away.
Now we have to get into General Relativity. (I promise I`ll be easy on you!) Einstein did not view gravitation as a force so much as a geometric configuration. Imagine, if you will, Bill Clinton snagging a leggy blond intern. After removing her panty hose he stretches them between the bedposts. Now, as he and his latest conquest remove jewelry and other items they toss these on top of the panty hose. What happens? The lighter objects make slight indentations on the surface of the hose. The heavy stuff (such as Bill`s little black book) make deep impressions on the hose. Now, when Bill rolls his wedding ring across the silk fabric (or cheap nylon), it does not move in a straight line but turns at the indentations in the fabric. Einstein viewed matter as bending the ``surface`` of the Universe in this manner. He saw gravity as being a matter of going down hill.
Vagueries in the motion of Mercury have proven his theory correct. (Einstein corrected problems in computation of orbits.) Anyone who has dropped a penny into a ``gravity well`` has seen just how this works.
This means that gravity can bend a beam of light; this effect is called the Gravity Lense, and is important if we are to understand why a black hole is black. Essentially, light can no longer strike the collapsing star. Gravity at the surface of the star is unbelievable, and the matter forms what is called a singularity. A singularity is a place where the mathematics which govern natural phonomena break down. Light can no longer strike the star, because it is being bent around it. This is called the event horizon
because we can no longer see or experience any events beyond this point. This is also refered to as the Schwarzchild radius
. Our star has disappeared from the perceptual universe.
Bear in mind, the total gravitational pull of the star remains the same (actually, it does grow a bit, as a result of swallowing up matter), but the gravitational attraction near the hole is tremendous. A normal star puts out radiation and solar wind, and has a magnetic field. A black hole has none of these, so black holes tend to suck in matter which comes too close (since they no longer have any repulsive forces). The diameter of the event horizon is generally a few miles.
For all intents and purposes, this object no longer exists as a part of our universe. Nothing can get out of the event horizon-not matter, not energy, not information. Black holes can only have three properties; Mass, Spin, and Charge.
(A black hole can spin, and can hold an electrical charge under some circumstances.)
Anything pulled below the event horizon is lost to our universe.
As a result, black holes act as great entropic sinks (contrary to what reader Tice with a J thinks
. Matter and energy enter, but they cannot leave, and this increases the overall entropy of the Universe, since that matter and energy is sequestered inside the hole. Since most stars are not single (like our sun) but are part of a binary system or cluster, matter is readily available to ``feed the beast``, and this is visible as an accretion disk. An accretion disk is like the whirlpool which forms when you pull the plug in your bathtub; it is a swirling vortex of matter and energy. Since most binary stars are relatively close together (Alpha Centari B is about as far from A as Uranus is from the Sun) there is usually plenty to go down the drain. This is all lost to the perceptual Universe we live in.
On exceedingly rare occasions a black hole can decay.
This happens because of quantum mechanicals affects; a charged black hole can form a particle and antiparticle (a virtual particle) just below the event horizon. (This happens all of the time in the perceptual universe, but since they are opposites they cease to exist immediately as they are in direct contact.) In a charged hole, if an electron and positron form and the hole holds a negative charge electromagnetic repulsion can split these particles, ejecting one from the hole while keeping the other. This ``particle fountain`` can eventually decay the hole.
On the topic of decaying black holes, I need to point out that our Universe itself bears an eerie resemblence to a decayed black hole. It started as a singularity, the so-called cosmic egg, which exploded for no apparent reason. This Big Bang started the Universe on a major course of expansion, and with it came stars and galaxies and the physical laws by which everything operates. Maybe we are inside of the event horizon of someone else`s Universe?
There is a theory which postulates the existence of white holes, which act as counterparts to black holes. The idea is that the black and white holes connect via a wormhole (which is like a tunnel cutting across ``underneath`` the surface of space-time. The matter absorbed by the black hole is ejected by a white hole. It was suggested that the Quasars
(Quasi-Stellar Radio Sources) were white holes. Quasars are the most distant objects know, and we really don`t know much about them, except they put out lots of radio waves and must generate unbelievable energies. This theory is no longer considered seriously, as black holes can account for the output of the quasars.
Oh, by the way, there may be a black hole at the center of our galaxy!
Another thing about black holes; they needn`t be formed from the great stars, as I have suggested in this piece. At the time of the Big Bang pressures on the newly liberated matter were immense, and black holes of all sizes could form. Many of these mini-black holes have disappeared through the process of decay, but we should eventually find some out there. It is thought by some that the Tunguska meteorite
which flattened forest land in Russia in 1908 may not have been a meteorite or comet at all, but a collision with a mini black hole. (The strange way the trees fell makes some people think that heavy tidal forces whipped through the forest.) Mini black holes can be asteroid mass and up.
Einstein showed that time is dependent on the observer. He also showed that the faster the observer is moving relative to an event, the slower time proceeds from his viewpoint. Also, the deeper into a gravity well an observer travels, the slower time seems to proceed to him. As a result, if you were to fly into a black hole, you would never make it. (Of course, tidal forces would crack you like a walnut long before you could come to the event horizon.) The closer you got to the singularity, the more time would stretch out so that you would fly for your entire life and never quite get there. You could spend a million years flying into the hole, but you would never reach it! That is from your vantage point, however; to the outside observer you would fly right in!
Just think what a boon that would be to your wine-cellar! You could buy new wine at bargain-basement prices, fly it close to the singularity, and bring it out aged to perfection! Of course, the cost of this little sortie may be a bit steep...
Finally, I would like to take a moment to think about the end of things. There are three options currently considered for the final fate of the Universe. If the Universe does not contain sufficient mass it will continue to expand. As matter gets farther and farther apart, entropic decay (the tendency to wind down) will result in a continual loss of heat/energy until the Universe reaches absolute zero. This is refered to as heat death. A second option is the Steady State; virtual quantum continue to form new matter in the gaps between galaxies, and the Universe continues along as it is. Not many people are Steady Staters any more. Finally, if there is enough ``dark matter``, matter we don`t see floating about, gravitational attraction could cause the Universe to contract. It will eventually crush down into a giant black hole. This is called the Big Crunch, and many astronomers believe that we are inside a giant oscillating black hole-ever expanding and contracting.
What of God in all of this? Well, what is beyond our meagre little Universe? Everything, including the Universe itself, moves; what of the unmoved mover? Our answers simply bring more questions. We are placing the world on the back of an elephant, which we place on the back of an elephant, etc. Darwinists would have you believe it is elephants all the way, while those of faith say that God lies at the bottom of the elephants.
Remember, in the Book of Genesis, God said ``Let there be light`` and there was light! Well, what happened when that cosmic egg exploded? There most certainly was light! Light is the measure of everything in this Universe, and the photon is the only thing we know for certain is real. Isn`t that an interesting concept? Isn`t it interesting that the author of the Book of Genesis understood this?
The study of such things should be a source of great humility for the Human race. Consider how puny and inconsequential we are in the grand scheme of things! We are like frogs in a pond; aware only of what is directly in front of our faces, while remaining blissfully ignorant of the majesty before us!
``There is more under Heaven and on Earth, Horatio, than is dreamt of in your philosophy`` according to the Bard. He was more right than he knew.
Anyway, I hope you diehards who stuck this out enjoyed it.