Page 1, Black Holes, Intro to Our Galaxy: [Next Page] [Class Home Page] Text Pages 326 - 328

A black hole is defined when V (the velocity) equals the absolute MAXIMUM: The speed of light, C. That is, the escape speed of a Black Hole IS the Speed of LIGHT!


Re-arranging things a bit from the previous page, and substituting C for V:

R = 2GM/C²

R is called the Schwarzschild radius: it is the radius at which a certain Mass, ANY MASS, will by definition, be a Black Hole.


Anything that is not able to stay in orbit and falls within the Schwarzschild Radius of the black hole, will leave this Universe forever. This is sometimes referred to as the EVENT HORIZON because this boundary keeps us from viewing anything inside of this radius. We are unable to see any light escape from within this radius, thus information about what is occurring within this radius, so called events, are never known outside of the Black Hole.


An object of ANY MASS can be a black hole, it just depends on what radius it is. The Larger the Mass, the larger the radius, but they will all be Black Holes.

Typical Radii for Black Holes of Different Masses:

• Radius of the Sun, if its to be a black hole: 6 kilometers.

• Radius of the Earth, if its to be a black hole: 2 centimeters.

• Radius of YOU, if you were to become a black hole: Size of an atomic nucleus.

• Radius of the Universe, if it were to become a black hole? Its present size! Our universe *is* a black hole!

What would happen if the Sun (for some inexplicable reason) became a Black Hole?




What would happen to Earth?