Gamma rays from the Crab nebula.Gamma rays Gamma rays Electromagnetic radiation emitted from excited atomic nuclei as an integral part of the process whereby the nucleus rearranges itself into a state of lower excitation (that is, energy content). from the Crab nebula Crab Nebula, diffuse gaseous nebula in the constellation Taurus; cataloged as NGC 1952 and M1, the first object recorded in Charles Messier's catalog of nonstellar objects. The Crab nebula, the optical remnant of a stellar explosion observed more than 900 years ago, is already known as one of the strongest sources of X-rays and radio waves Radio waves Electromagnetic energy of the frequency range corresponding to that used in radio communications, usually 10,000 cycles per second to 300 billion cycles per second. . Now a team of astronomers has established that the Crab nebula is also a steady source of highly energetic gamma rays. "We have seen a very clear signal from the Crab nebula," says Trevor C. Weekes of the Harvard-Smithsonian Center for astrophysics The Harvard-Smithsonian Center for Astrophysics (CfA) is located in Cambridge, Massachusetts. It consists of the Harvard College Observatory and the Smithsonian Astrophysical Observatory. The Center is located at 60 Garden Street. in Cambridge, Mass. "It's a completely steady source of gamma rays." The energy source powering the crab nebula is most likely a rotating neutron star, which has a highmagnetic field and can accelerate electrons to relativistic rel·a·tiv·is·tic adj. 1. Of or relating to relativism. 2. Physics a. Of, relating to, or resulting from speeds approaching the speed of light: relativistic increase in mass. energies. These accelerated electrons interact with low-energy photons in the region surrounding the neutron star to generate gamma rays. The resulting gamma rays typically have energies exceeding those achievable in any particle accelerator or collider col`lid´er n. 1. (Physics) a The steadliness of the signal establishes the Crab nebula as a standard against which to measure other gamma-ray emissions. A number of research teams have previously detected high-energy gamma rays from cosmic sources, but nearly all these signals proved sporadic and unpredictable. The existence of a single, well-understood source of cosmic gamma rays may help astronomers interpret other, more puzzling gamma-ray observations. "The Crab is a weak gamma-ray source, but it's the strongest source yet detected," Weekes says. "It provides a standard signal." |
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