for National Geographic News
For centuries astronomers have trained their gaze on the matter that brightens the universe: the moon, the planets, the stars, and the galaxies. But these bright spots only comprise four percent of the cosmos.
The rest is seemingly a void, nothing but darkness. But the darkness is not empty: It is filled with dark matter and dark energy that has, over the course of the 14 billion years since the big bang, molded the universe into the dynamic structure and shape it holds today. The big bang is the name given to the theory that the universe started with a single cosmic explosion.
Welcome to the dark side.
In a series of papers presented in the June 20 issue of the journal Science, astrophysicists document what is known and waiting to be discovered about the 96 percent of the cosmos that can't be seen.
"We are incredibly lucky to be working just at the moment when the pieces of the cosmic jigsaw puzzle are falling into place, locking together, and revealing the outline of the pieces yet to come," writes Robert Kirshner, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, in the paper on dark energy.
Any exploration on the dark side of the universe would not be complete without a look at black holes: the mysterious voids that seem to suck in all matter that comes within their reach and are blamed for the disappearance of everything from a favorite pair of earrings to notorious criminals.
In reality, black holes are places where gravity is so strong that once something crosses their horizon it will never escape, not even light. But in the process of their consumption they may have helped develop galaxies and the structure of the universe.
Mitchell Begelman, an astrophysicist at the University of Colorado at Boulder and author of the review paper on black holes says that to understand the stars, galaxies, and the gas that lies between them, it is necessary to understand black holes.
"Black holes are not really pathological places that are strange in the normal scheme of things," he said. "In fact, the structure of the galaxies and how they and the planets and ultimately life form could be directly affected by what happens close to black holes."
While it is true that once something crosses their horizon it will never escape, only a small fraction of the material that comes under the influence of a black hole is actually sucked in. The rest is expelled as excess energy.
Research shows that black holes can only consume material that spins at a relatively slow speed, so as an object falls into a black hole it gives off all the excess energy to material that is farther out.
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