Black holes are formed when massive stars collapse in on themselves after exhausting their nuclear fuel. The collapsed star becomes incredibly dense, with such strong gravity that not even light can escape. There are two main types - galactic black holes, which are relatively smaller and formed from collapsed stars, and supermassive black holes, which are millions to billions times the mass of our sun and reside at the center of most galaxies. The event horizon marks the point at which a black hole's gravity becomes so intense that nothing, not even light, can escape.

1. Black Holes An Interactive PowerPoint By: Mike Micallef

2. Black Holes What Are They? How Are They Formed? Galactic Black Holes Supermassive Black Holes Black Hole Growth The Event Horizon Gravitational Lensing Black Hole Video About Me Resources Exit Exit

3. What Are They? In short, a black hole is an imploded star. When a massive star undergoes a supernova explosion, it may leave behind burned our stellar remnant. With no outward forces on these remnant, the star collapses on itself, to a point with no volume and infinite density. The gravitational force from this point is so vast that light itself cannot escape the gravitational field, and therefore gets sucked up into the mass itself. Thus creating a black hole. No, those aren’t stars. They’re black holes. As seen through an X-ray Telescope.

4. What Are They? (Cont.) Contrary to popular belief, black holes are not stellar vacuum cleaners. Instead they only affect what cannot escape their gravity. If you replaced the sun with a black hole of the same mass, we would not be sucked up into that black hole, instead our orbit would remain unscathed. To be “sucked” into the black hole, you must pass over the event horizon, or the point in which gravity is so strong, not even light itself can escape. As the example state above, the event horizon of the black hole replacing the sun would be approximately 3km. Compared to the nearly 700,000km radius of the already present sun. Exit

5. How Are They Formed? Although a black hole has not been discovered, the idea of one is widely accepted among the scientific community. A black hole is formed when a star runs out of stellar fuel. When the star burns this fuel, it creates an outward force, which counters the force of gravity. When this force is gone, such as when the star burns out, the only force left acting upon the matter is gravity. Thus pulling all the matter towards the center of the star, and causing an extremely dense ball of matter. Sometimes the matter can collapse in a fraction of a second. The combined gravitational force, and speed in which it collapses creates the tiny ball of matter in which we call a black hole. Exit Formation Video

6. Galactic Black Holes Astronomers have found that the Milky Way Galaxy contains millions of black holes. Some part of binary star systems, others just collapsed stars. In the binary star systems containing black holes, the black hole actually rips gas off of the star. The gas falls violently into the black hole. Since the gas particles are moving so fast, they create friction against each other to heat up the area around the event horizon to a few million degrees, thus radiating x-rays, which is our evidence of the black hole’s existance. Astronomers believe that a number of binary systems contain black holes, largely in part to the large amount of x-rays emitted, and the extreme velocity of the remaining star. Exit

7. Supermassive Black Holes Astronomers also believe that there are supermassive black holes at the center of every galaxy. Somewhere in the range of one million to one billion solar masses. This would keep the galaxies in the groups that we find them in, and in the shape they are in. There is strong evidence that there is a supermassive black hole in the center of the Milky Way galaxy. This would keep everything in a spiral shape, rotating around it. Also there is an extreme radio-wave source called Sagittarius A* (SgrA*). The clearest indication of the presence of a black hole is the speed in which the stars rotate around SgrA*. Since they rotate so fast, and are so close to the center, the only thing that could create the gravitational force to keep everything in orbit and not be visible or interfere with the stars orbit is a black hole. Exit

8. Black Hole Growth Once a black hole is formed, it can continue to grow by absorbing more matter. Every black hole will continually absorb cosmic dust and radiation but the amount is so small it does not affect the overall mass of the black hole. If the black hole is in a binary star system, that would significantly affect the mass. Or if the black hole were to collide with another stellar object such as a star or planet. This is the proposed formation of the supermassive black holes in the center of the galaxies. Exit

9. The Event Horizon The event horizon is a very important piece of the black hole puzzle. The event horizon is the point in which a black hole’s gravity is so strong, that the escape velocity (the speed needed to escape the objects gravity) is greater than the speed of light. This is important because there is nothing that can travel faster than light itself, thus causing everything that crosses this theoretical field, to be permanently enveloped into the black hole. This is also one of the main reasons for creating the particle smasher in Europe, to help study this phenomena. Exit

10. Gravitational Lensing A gravitational lens is when light from a very distant object is “bent” around a very massive object. This is a very strange phenomena. When the massive object, such as a black hole, is directly in between the observer and a distant object the object seems to bend around the black hole and appear distorted. Gravitational lensing is not only caused by black holes but also by large stellar objects. Exit

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12. Who Am I? My name is Mike Micallef. I am a student at Grand Valley State University, and an aspiring teacher. I hope to one day teach physics back in my hometown of Hartland, MI. You can reach me for any additional information at my email: [email_address] . Exit

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14. Resources Many Thanks to: NASA Stephen Hawking For his research on black holes. Google (Images) All images are artist’s depictions of black holes. WikiPedia Discovery Channel Exit