The Makeup of a Black Hole
The point of the Black hole at which all of the mass of the former star is concentrated at is called a singularity. It gets this moniker because all the mass is crushed together by the force of gravity until it becomes a point of infinite density, but yet it takes up virtually no space. Every black hole has at its center a singularity. Black holes also have what is called an event horizon. The event horizon is where gravity’s pull is so tremendous that nothing can move outward from the black hole, only in towards the center. It’s called an event horizon because nothing about the events happening beyond this horizon are known. Because light cannot escape from a black hole, we cannot actually ‘see’ a black hole. The existence of a black hole must be determined from events happening around it. One of the most common is to observe gas and dust particles being ‘torn off’ from a star. Since stars have tremendous mass, only something with more mass could pull the gas or dust from the star.
The black hole also can be ‘weighed’. By measuring the speed of the light of the companion star as the star comes towards and away from the earth, an effect known as the Doppler shift, the velocities can be determined. The faster the velocities mean a faster orbit for the companion star, which means the stronger the gravity pull on it. This necessarily means the black hole has more mass.
If a black hole only has an event horizon and the singularity at the center, it is known as a Schwarzschild black hole in honor of the German physicist Karl Schwarzschild who used Einstein’s equations of general relativity to predict a black hole would form. A Schwarzschild black hole has no spin or charge associated with it. A Reissner-Nordstrom black hole does have a charge associated with it. This charge causes an inner event horizon and an outer event horizon to form. The outer event horizon funnels matter and light toward the inner event horizon. Once inside the inner event horizon, the light continues toward the singularity, but it’s no longer funneled towards it. It will eventually get to the singularity. A Kerr black happens when there is a spin present. This causes the singularity to become a loop or ring. It also causes an Ergosphere to form. While in the ergosphere, light is bent toward the singularity but some of it can still escape.