N A K E D S I N G U L A R I T Y
The cosmic quicksands
by Glenn Santos
Philippine Science High School

What happens when a star dies?

When a star runs out its solar fuel, it will explode into a nova or supernova. The remaining mass condenses into either a white dwarf or a neutron star. White dwarfs are the result of a collapse of a star whose mass is less than 1.4 solar masses (1 solar mass = mass of Sun), and is formed from the remnants of a planetary nebula. On the other hand, neutron stars are created from the debris of a supernova explosion of a star that has a mass between 1.4 and 3 solar masses. It would continue to shrink until it would blink out of existence. It would become a black hole.

Black holes are the remnants of a neutron star that collapsed upon itself due to its immense gravitational force. Its gravity is so strong that not even light can escape from it! The collapse of the neutron star is determined by a critical radius called the Schwarzschild radius. If a star is compressed into radius smaller than Schwarzschild radius, it becomes a black hole. The black hole is compressed into a singularity, a point in its center. The event horizon, a point of no return, of the black hole is the spherical area around the hole where the escape velocity is just equal to the velocity of light. The Schwarzschild radius of a black hole is just the radius of the event horizon.To find the Schwarzschild radius of a star, just multiply the star's mass in solar masses by 3km.

Karl Schwarzschild Even though interest in black holes only emerged during the 20th century, thoughts about the existence of black holes started way back in the 18th century. A French mathematician Pierre Simon de Laplace made a treatise at this time about "black stars". He reasoned that when the mass of a star is increased, its gravitational pull would proportionally increase. Eventually even light particles would not be able to leave its surface and the star would become invisible. Albert Einstein stated in his special theory of relativity that nothing can go faster than light. This made Laplace's black stars into holes where nothing can escape. After the release of Einstein's theories, German astrophysicist Karl Schwarzschild calculated for the critical radius when a star would implode into a black hole based on those theories.

Black holes are particularly difficult to find especially when they are all alone. The strong pull of black holes does not permit anything to escape it, so scientists are relying on indirect ways of detecting them. Many stars come in pairs and are called binary systems. If one of the two stars turns into a black hole, a disk of matter from the other star would sink into the black hole. As the matter swirls into the hole, it heats up to very high temperatures and emits X - rays.

Detecting and observing dust and gas clouds are also good methods of finding black holes. It is similar to the way black holes are found in binary systems. The cloud forms a disk around the black hole or it rotates around an axis if the black hole is located in its center.

Some scientists believe that the center of most galaxies are black holes. Observations reveal that many galaxies, even our own, show high concentrations of matter in their centers. They concluded that the core was a black hole, because only a structure of this type can concentrate a small amount of matter in such a small space (around several billion solar masses into a sphere of a light year in diameter). Evidence also shows that the galactic cores are too dark to be stars or star clusters.

Quantum mechanics states that a black hole would eventually destroy itself. The black hole would emit radiation from its center. As it releases this radiation, it shrinks and its rate of release increases so that it would completely disappear.

A ideas have sprung about black holes. One is the idea of "white holes". Once you hit the singularity of the black hole, it is theorized that you would be spitted out through a white hole. A white hole is an exact opposite of a black hole. It is said that it can only spit out things the same way a black hole can suck in things. Though proven mathematically, we cannot be certain of their existence.

Another idea is of a "wormhole". A wormhole is, simply put, the system of a white hole and a black hole. It is just an imaginative idea, because if white holes don't exist, wormholes don't, too.

Black holes come in many varieties. They have different masses, may be charged or not, rotate or do not rotate, and so on. Normally, scientists only refer to non-charged, stationary black holes since it is difficult to explain the other types.

Due to its structure and density, black holes produce strange effects on the things that fall into it. Imagine you are traveling towards a large black hole . As you near the event horizon, you shut off your engines and go into free fall. Tidal forces begin to act on you as you fall nearer and nearer the center. You feel as if you are being stretched. The images of far away objects seem to be distorted because of the black hole's pull. It would take you a few minutes to reach the horizon (faster if the black hole was smaller) and several seconds before you hit the singularity. Theoretically, this event is inevitable since nothing can escape the hole.

NOTE: Contrary to popular belief, black holes DO NOT suck in everything within reach. If the object is far enough in the horizon and has enough energy to escape the pull of the hole, it is possible that it can get away!

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