Black Holes: A great mystery of the universe

Black holes are one of the greatest mysteries of our universe. However, using just a few concepts that we have learned in class, we can understand the basic constructs of black holes. A black hole is the result of a single point in space containing extreme mass (this point is called a singularity). Similar to how we observe planets and stars exert gravitational force on nearby objects, a black hole singularity exerts a very strong gravitational force. Additionally, we know that celestial bodies all have unique escape velocities that depend on the bodies force of gravity (which is proportional to M/(R^2)). Escape velocity is the speed which an object must reach in order to escape from a gravitationally bound orbit. Because a black hole singularity is a point of immense mass, it has an extremely high escape velocity at nearby locations in space. What we call a “black hole” is really the spherical area of space in which the escape velocity from the black hole singularity is greater than the speed of light. This means that inside the black hole, no light (or any other particle) can escape. Because no light can escape this sphere of space, the region of space looks completely black to any outside observer. This is why it is called a “black hole.”

Black Hole Visualization

Despite the relatively simple physics that describe the construct of a black hole, there are many aspects of black holes that are still mysteries to even the greatest physicists/astronomers.

1. We know that “smaller” black holes are formed from the collapse of massive stars (at least 20 times as massive as the Sun). However, it is still unclear what forms the supermassive black holes that exist at the center of every large galaxy in our universe. These supermassive black holes are essential to our universe; yet their origins are quite a mystery.
2. The physics behind black hole singularities and the points in space very close to black hole singularities are not clear. These singularities seem to be points at which space-time just collapses, but what physical properties govern that collapse, and what this means for the nature of our universe is not known.
3. If supermassive black holes are at the center of large galaxies and galaxies often orbit in galaxy groups or clusters, might there be “super-super massive black holes” at the center of some large galaxy clusters?