Black Holes

Loosely speaking, Black holes are thought to be formed when massive stars collapse under their own weight down to a singularity (a point). Due to this process they become a new type of object. One with an infinitely small radius, a singularity; roughly the same mass they had before the collapse; and therefore, an infinite density. Since the force of gravity is inversely proportional to the square of the distance between two masses, the gravitational force on any mass increases to infinity as the mass nears the singularity. It is this increase to infinity that provides Black Holes with their oddest propertities.

The escape velocity of a body is defined as the minimum velocity with which it must be projected from a surface such that it will not return. The escape velocity can be calculated by equating 'the amount of energy that must be supplied to a body of mass "m" such that it will reach infinity with a zero velocity' with its 'change in Kinetic Energy over the same period.'

In this equation: R is the initial radial distance from the center of the body one is escaping from (the singularity) and M is the mass of that body. Since the distance between the bodies ("R") goes to zero, it is easily seen that there has to be some distance at which the escape velocity is equal to the speed of light. That is the distance (radius) that is normally assigned to be the "size" of the Black Hole. For shorter radii, the escape velocity exceeds the speed of light and nothing, even light, can escape from within the black hole.

The fact that light cannot escape from a Black Hole is generally taken to mean that Black Holes are invisible. In actuality, due to simple optics concepts, this inferrence cannot be true. In fact, asside from our sun (due to its proximity), Black Holes should look like the brightest stars in the night sky.

Stars radiate approximately equally in all directions arround their surfaces. They are so far away that we see them as points in the sky rather than extended disks. In essence we see one ray of light from each star. That is unless there is a large gravitational field in the sky that bends a second ray to us. In that case we not only see the star in its original location from the direct ray, we also see an image of the star from the redirected ray. As with mirrors, the image would look to us as a second star in the sky located directly back along the redirected ray. Due to the longer distance traveled by the redirect ray, the image would, of course, be a little dimmer than the original star.

The really interesting thing about Black Holes, is that their Gravitational field is so strong that every light source in the sky (star, galaxy, etc.) will be imaged arround the perrifery of the hole. Additionally, it dosen't even matter where the earth is. Since every light source in the universe, emits a ray in every possible direction, every point in the universe would see exactly the same thing; just using different rays.