Physics: Principles and Problems



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X Marks the Spot for Black Holes
Posted September 2002

They are the most powerful forces in the universe. They are so powerful that nothing can escape them - not even light. They are black holes - supermassive stars that collapsed upon themselves millions of years ago. Their mass is so large that when they collapse, their gravity pulls in everything around them.

Even though light has no mass, it is affected by gravity. When light comes too close to a black hole, it is bent towards gravity. If the gravity is strong enough, the light is bent so much that it will never escape. Because light can't escape black holes, they cannot be seen by conventional methods. They appear as black nothingness in space.

Some scientists believe that occasionally, black holes encounter each other in space and collide - each trying to pull the other into its grasp. When this happens, monumental bursts of gravitational waves are emitted, causing ripples in space-time.

The colliding black holes leave their mark, an X to mark the spot. The black holes spew out jets of matter and radiation in opposite directions, similar to two balloons attached to each other as they release air. This spewing of matter and radiation can last as long as a billion years, forming ejection plumes thousands of light-years long.

Most scientists agree that in the center of every galaxy, including our own Milky Way, is a black hole. Sometimes galaxies themselves collide, and in these cases the internal black holes will collide as well. Of course, because galaxies are primarily filled with empty space, they do not crash together, instead they affect each other with their gravitational fields.

Scientists are trying to find evidence of black hole collisions, but they are rare. Even those that have occurred, happened millions of years in the past, and scientists are simply able to look at the end results. It is like shattering a watch and trying to figure out how it worked beforehand.

Because there are so few colliding black holes in the observable universe, and there is no way to predict if any will happen in the near future, scientists have turned to computers for an answer. Using computers, scientists have simulated these situations, but the models break down when the black holes approach one light-year from each other.

Computer modeling evidence has led some scientists to believe that colliding black holes are less realistic. However, others believe these X-type radio sources, shown on the models, are the "smoking gun" that proves this sort of thing happens in the universe.

Use the Internet to research black holes. Make a poster for the class that explains how scientists can "see" black holes.



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Physics: Principles and Problems