Crab Nebula (redirected from Messier Object 1)

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. It is the remnant of a supernova that was observed in 1054 by Chinese and Arab astronomers to be as bright as Venus; markings in northern New Mexico depict a star near a crescent moon that might be a record of this supernova. Only three other supernovas have been observed in our galaxy since then. The explosion of the Crab Nebula produced a large expanding shell of delicate filaments. The filaments contain ionized gas in which unusually energetic electrons twist through magnetic fields at speeds close to that of light, emitting synchrotron radiation. Although this radiation is what makes supernova remnants visible in radio wavelengths, in this nebula it is so strong that observers can see the filaments through moderate-sized optical telescopes under good conditions. The nebula is also a strong emitter of X rays. At its center is a pulsar, PSR 0531+21, that spins 30 times per second. The youngest pulsar observed, it gives off radiation at radio, optical, ultraviolet, X-ray, and gammay ray wavelengths, as well as electrons that power the synchrotron radiation in the surrounding nebula.

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Crab Nebula

Bright nebula in the constellation Taurus, about 5,000 light-years from Earth. Roughly 12 light-years in diameter, it is the remnant of a supernova, first observed by Chinese and other astronomers in 1054, that was visible in daylight for 23 days and at night for almost two years. Identified as a nebula c. 1731, it was named (for its form) in the mid-19th century. In 1921 it was discovered to be still expanding; the present rate is about 700 mi/second (1,100 km/second). The Crab is one of the few astronomical objects from which electromagnetic radiation has been detected over the entire measurable spectrum. In the late 1960s a pulsar, thought to be the collapsed remnant star of the supernova, was found near its centre.

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Crab Nebula [′krab ′neb·yə·lə]

(astronomy)

A gaseous nebula in the constellation Taurus; an amorphous mass which radiates a continuous spectrum involved in a mesh of filaments that radiate a bright-line spectrum.

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Crab Nebula 

a galactic nebula, the result of a supernova explosion in 1054 in Taurus. The distance to the nebula is 1,700 parsecs, and its radius is about 1 parsec. It is expanding at a speed of 1,000–1,500 km/sec. The nebula has the form of an elongated ellipsoid and a filamentary structure. The total mass of gas in the Crab Nebula is about 0.1 solar mass. About 80 percent of the nebula's luminosity (it has a visual stellar magnitude of 8.5) is concentrated not in the filaments but in the amorphous mass occupying the interior of the ellipsoid.

The Crab Nebula is a source of radio emission (Taurus A). In the interval between the radio and the optical regions of the spectrum there is a noticeable maximum in the radiation, the nature of which is not yet known. In the direction of shorter wavelengths, the spectrum extends to the X-ray region; only the central part of the nebula and the star itself radiate in this region. The radiation of the amorphous mass at all wavelengths is produced by fast (relativistic) electrons (with energies of 10⁸–10¹² eV) moving in a magnetic field (of intensity 10^-3 oersted, or 8 X 10^-2 A/m); this is what is known as synchrotron radiation. The generation of particles and of the magnetic field is associated with the remnant of the supernova, which is a pulsar with a radius of about 10 km, rotating with a period of 0.033 sec and producing bursts of optical, X-ray, and radio radiation. The star has a magnetic field of large intensity. The rapid rotation of this field produces electromagnetic effects, resulting in the acceleration of the particles and bursts of radiation. The field itself “twists” and then expands into the nebula. The pressure of the field and the particles accelerates the expansion of the nebula.

The study of the Crab Nebula, a unique celestial object, has made it possible to solve a number of problems of stellar evolution connected with the origin of pulsars.

S. B. PIKEL'NER