An artist's concept of a black hole, surrounded by an accretion disk. The gas in this disk is heated to millions of degrees Celsius and emits X-ray radiation.
Credit: Nasa/Honeywell Max-O digital group/Dana Berry.
The brightest lights in the universe often come from the blackest pits of deep space.
Black holes, so named because even light cannot escape their gravitational grasp, can only be sensed through their tug on other matter. While black holes themselves are invisible, the regions around them are reigned by powerful magnetic and gravitational forces that create some of the most luminous radiation ever seen.
Super-bright anomalies like cosmic rays, plasma jets and gamma-ray bursts pour forth to fly across the universe, and researchers are just beginning to untangle the mysteries of how they arise.
Black holes are extremely dense masses jammed into single points of space. At their centers, all the matter is crushed to infinite density inside a space of zero volume, called a singularity. There, the pull of gravity is thought to be infinitely strong, warping space-time to be infinitely curved.
Yet, for all the bizarre happenings inside black holes, if you are sufficiently far enough away from them, they act like any other matter. That means that if the sun were replaced with a black hole of the same mass, all the planets would continue to orbit around it just as usual, scientists have said, though Earth would not be habitable due to lack of sunlight.
Black holes are thought to form during the explosive deaths of very massive stars. When a star exhausts all its fuel, it implodes under the crushing force of gravity into a denser and denser ball, eventually reducing down to a black hole. Meanwhile, the outside layers of the star are expelled in a powerful blast called a supernova.
Rays, bursts and jets
Scientists think some of the energy released by the explosion and formation of a black hole goes toward accelerating particles to great speeds, creating marvels called cosmic rays that fly through the universe at almost the speed of light. We detect some of these particles on Earth, where they still pack such a punch they can knock out electronics systems.
Another consequence of black holes and supernovas are short flashes of high-energy gamma-ray light called gamma-ray bursts. They originate in distant galaxies and are the brightest things ever seen in the universe. The bursts likely arise when a very massive, rapidly-rotating star collapses into a black hole during a supernova explosion, and releases a short, intense beam of gamma-ray radiation.
And black holes also seem to be to blame for the jets of hot charged gas seen spewing from the hearts of distant galaxies. These galaxies, called blazars, likely have supermassive black holes in their centers that are warping space-time in extreme ways. As dust and gas gets dragged toward a black hole, some of it is spit back out and accelerated by twisted magnetic fields around the black hole to shoot out in luminous jets that can be seen across the universe.
"We studied a battery mechanism to extract the energy of a spinning black hole, and it provides a compelling way to power jets in high-energy gammaray sources," said Govind Menon, a professor of physics at Alabama's Troy University.
Menon recently wrote the book "High Energy Radiation from Black Holes: Gamma Rays, Cosmic Rays, and Neutrinos," (2009, Princeton University Press) with astrophysicist Charles Dermer of the Space Science Division of the Naval Research Laboratory. The two scientists spoke about the topic Nov. 4 at the 2009 Fermi Symposium in Washington, D.C.
The researchers said even more secrets of black holes are likely to be discovered soon thanks to new experiments like the Fermi Gamma-ray Space Telescope, the South Pole IceCube Neutrino Experiment, ground-based TeV (1000 GeV) gamma-ray detectors, and the Pierre Auger Cosmic Ray Observatory in Argentina.
"This is a decade of incredible scientific discovery in high-energy astronomy and astroparticle physics," Dermer said.
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