Union University
Union University Department of Physics

The Science Guys



Science Guys > October 2002

October 2002

How can you prove that there's such a thing as black holes in outer space and what would happen to you if you got next to it?

If a star is massive, it can undergo a cataclysmic explosion called a supernova. During this process gravity crushes the star’s materials, protons and electrons, into neutrons forming a neutron star. (A teaspoon of a neutron star would weigh billions of tons.) For stars several times the mass of our Sun, the crunch continues until an extreme amount of matter is in a tiny region of space and the gravitational field becomes so great, we call it a black hole.

Strange things can occur as you near a black hole. If you are near enough to a black hole, the gravitational pull on your feet would be much greater than on your head. Physicists call these force differences tidal forces. On Earth, there is a different gravitational field at our feet than at our head, but the difference is insignificant. However, the difference near a black hole can be extreme, leading to one’s body or a spaceship being ripped apart.

A black hole allows nothing to escape, not even light, so the evidence for black holes is necessarily indirect. We cannot look with a telescope and see one directly. However, we can observe objects near a black hole. Even objects far from a black hole are affected by the black hole’s gravity. The visible stars of some galaxies are observed to be whirling about the galactic center with speeds that imply a very massive object at their center. The most likely candidate is a black hole. Indeed, astrophysicists believe that our galaxy contains a black hole at its center with a mass greater than one million Suns. The galaxy NGC4261 has a core over one billion times more massive than our Sun, yet we see no star or star cluster at its center, which implies a black hole must be there.

As matter falls into a black hole it speeds up and emits --ray radiation before being totally absorbed by the hole and disappearing out of existence. X-rays are emitted from the cores of galaxies where black holes are believed to lurk. This gives further indirect evidence for black holes. Some stars also orbit an invisible companion. This mysterious companion draws gases from the star that end up orbiting it in what is termed an accretion disk. As material from the disk falls to the center, x-rays are produced. The only concept we currently have to explain this phenomenon is the black hole.

The dream of some physicists is to make a baby black hole in the lab and subject it to close scrutiny. However, there is still considerable debate over actually doing this. This seems to be the only way we might ever get "up close and personal" with a black hole.