Black Holes, in general, have developed a certain hype. It has been said that they are an important key in developing portals to other galaxies. Supposedly in a Black Hole, time and space do not exist; there is no space to travel or time to pass. Recent writings have also claimed that when two Black Holes form a connection between each other they become what has been labeled as a "Wormhole". These "Wormholes" are considered to be portals that can take you from one point in the universe to another instantly - no matter the distance between these points. The reasoning behind such a claim is that since time and space do not exist in a Black Hole, the distance between two objects is irrelevant. This is because distance is a measurement of space, which theoretically does not exist. If you are having difficulty understanding this concept, try the following experiment: Take a sheet of paper and draw a dot at the top and bottom ends of the paper. Label the dot at the top end of the paper "Point A", and the dot at the bottom end of the paper "Point B". Now draw and measure a line between the points A and B (refer to diagram 1). Next, fold the paper so that Point A is lying directly over Point B (refer to diagram 2). Finally, stick a pencil through the two Points, and measure the distance the pencil has had to travel to get from Point A to Point B (refer to diagram 3). Upon completion of this experiment, you should easliy have been able to imagine how two Black Holes - like the two adjoining points (A & B) - come together to form a Wormhole, no matter what the original distance between them.

Diagram 1:

Diagram 2:

Diagram 3:

To understand Black Holes, you must first understand some other components of the universe. Firstly, you must understand that every body of mass exerts a certain amount of gravitational pull on other bodies of mass. For instance, when you write with a pencil the mass of your body exerts a gravitional pull on the pencil towards your hand, and vice versa. Now, there are those of you who are going to ask, "How can this be true?".If you were to place a pencil on the desk, then place your hand on top of it, then according to what I just explained the pencil should stick to your hand because of the gravity your hand is exerting on the pencil. But we all Know, hopefully, that this is not what happens, and infact the pencil stays on the table's surface. So how do I explain this? First I want to point out that the earth is also exerting it's gravitional force on the pencil in the opposite direction. Earth's gravitational force is much larger than that of anyone's hand, because it is so much more massive. Note: be careful not to misinterpret what I have just said. Though the Earth applies a stronger gravitational force than that of your hand, this does not necessarily mean that the ratio of mass to force is greater for Earth than your hand. The second concept you must understand is the life cycle of stars. An understanding of why stars go through this cycle is very important. Once a star has undergone a supernova, the core of the star may become a neutron star. This neutron star is so tightly packed with neutrons, that the star's density becomes much larger than that of our sun, though its radius may vary between 6 to 15 miles.If after the supernova, the star has a remaining mass greater than two or three solar(sun) masses, it becomes impossible for a neutron star to form. In such a case the remnants of the supernova continue to collapse into one central point. This point now becomes a black hole. This newly formed stellar object, develops such a powerful gravitational field, that no form of energy or matter can escape from it. Not even light can avoid it's influence; hence the color black - which is formed by the absence of color (light).



Comparison
The diagram above is a comparsion of the sizes of Our Sun,
A neutron star, and a Black Hole. The diameter of Our sun is
870,000 miles, while the diameter of the neutron star
can vary between 12 and 30 miles. The Black hole is smaller
than both the neutron star and Black Hole in diameter,
due its extremely powerful gravitational field.

You might be asking yourself,"Now what does all this and that shifting have to do with locating black holes?" Remember that light is a wave, and that all waves are subject to Doppler Shifting. Light waves are what allow us to see objects. Without light the human eye would not be able to perceive anything except blackness. Applying Newton's Law of Inertia to light waves passing by a black hole, you should be able to see that the light waves will bend dramatically towards a black hole. This is one sign that scientists use to locate black holes. Some light waves are sucked into the Black Hole, and some are far away enough to escape it, but their path of travel is nevertheless, affected (usually bends towards the black hole). Still other light waves are somewhere in the middle and they soon find themselves orbiting around the Black Hole much like the earth orbits around the sun. This means that the light orbits the Black Hole in an eclipse. This also means that like the earth's velocity (distance/time) changes as it rotates around the sun, so does the light around the Black Hole. Now if we know that the velocity of the light changes, then we also know that the frequency changes. Moreover, like the Earth, light's velocity change is consistant. This means that if you were to look at the frequency of a light wave at any given point of it's revolution, and compare it to the frequency of that same point 'X' number of revolutions later, it will virtually be the same. So what does this mean? Well, this means that the light has a definite period of time where it is moving away from the Black Hole on the light's orbit. According to the Doppler Shift, when the light is moving away from an observer then the frequency is decreasing, which means the light is red shifting. This means the light around the Black Hole seems to become increasingly red. If the light has a period when it is moving away from the Black Hole, it also has a period in which it moves towards the Black Hole. According to the Doppler Shift when the light is moving toward an observer, then the frequency is increasing, which means the light is blue shifting. This means the light around the Black Hole seems to become increasingly blue. If you are having a hard time visualizing what has just been said, refer to the diagram below.

The following is an actual picture, taken by the Hubble Telescope, of the Doppler Shifting of light waves around a Black Hole.

This page was written by Lionel Nimmo in the Astronomy class of BCC/Broward county July 1998