One of the few remaining mysteries of science is the black hole. When a star runs out of fuel to keep it burning, it explodes into a supernova(Intro. to Black Holes 1) After a supernova, some of the matter that was blown off leaves in pockets to different places in space. These pockets contract to from a pulsar, or new born star. The rest of the matter left from the massive explosion of the supernova comes back together forming a neutron star. If the dead star was too massive, the neutron star will be so large that its own gravity will crush it(Intro. To Black Holes 1). This is called its maximum density(Filkin 202). After all of the matter has collapsed in on itself, it becomes a black hole(Filkin 202). After being compressed infinitely, almost to nothing, the point in space that it makes is called a singularity(Filkin 216). The singularity is the bottom of the black hole.

Every stellar body has an escape velocity(Intro. to Black Holes 1). The escape velocity is the speed at which one must be going to escape the gravity of the object in question(Intro. to Black Holes 1). The Earth s escape velocity is seven miles per second(Intro. to Black Holes 1). This means that to leave the Earth s gravitational pull, you must be able to travel at least seven miles per second(Intro. to Black Holes 1). To escape a black hole, your velocity must reach at least the speed of light(Intro. to Black Holes 1). Because the speed of light(186,000 miles per second) is not possible because you must have infinite force to achieve the speed of light, nothing can escape a black hole s gravitational field(Intro. to Black Holes 1). This is why a black hole is a black hole. No light can escape from it, therefore, we cannot see it.

A binary star system consists of two stars that orbit around each other. They were discovered by Yakov Zeldovitch(Filkin 224). Sometimes, one star in a binary star system will die and become a black hole. When this happens, the force of the black hole s gravity will literally suck the matter away from it s sibling, and in doing this emitting X-rays that can be received on Earth(Filkin 225). This is one way that astronomers can find black holes.

It is possible that our galaxy is powered by a black hole(Freedman 69). Astronomers Linda Dressel, Tim Heckman, Roeland Van Der Marel and Meg Urry are looking into this(Olson 48). Because you cannot see a black hole, you can use one of two other ways to find it(Intro. to Black Holes 1). First, if a star is sighted that was circling something that could not be seen, that object is likely a black hole(Filkin 224). Second, view X-rays that are given off by the black hole through the use of radio telescopes(Filkin 225).

In a galaxy without a black hole at the center, stars closer to the center would move slower than those on the outside(Olson 51). On the other hand, if the galaxy is indeed powered by a black hole, the force of the black hole will make the stars near the center move the fastest(Olson 51). The object in the center of the Milky Way Galaxy is named, Sgr A*(Freedman 69). The stars in our galaxy that are closest to Sgr A* move at about 900 miles per second(Freedman 69). That means that the mass has to be about 2.5 million solar masses compacted into a space no larger than our solar system(Freedman 69). With a density of that magnitude and orbits of that speed, it is most certainly a black hole(Freedman 69).

Works cited:

Filkin, David. "Stephen Hawking s Universe." New York: Harper Collins

Publishers, Inc., 1997

Freedman, David H. "The Mysterious Middle of the Milky Way." Discover.

November 1998: 66-75

"Introduction to Black Holes" n. pag. Online. America Online. 18 April 1999.

Available: http://www.damtp.cam.ac.uk/user/gr/public/bh_intro.html

Olson, Steve. "Black Hole Hunters." Astronomy. May 1999: 48-55