Crab Nebula

The Crab Nebula

Crab Nebula

In the year 1054 Chinese astronomers and other sky watchers saw what they thought was a bright new star and is now thought to have been a supernova. Today's astronomers think that this exploding star created the Crab Nebula (also known as M1 and NGC 1952), a supernova remnant.

In the 1960s the pulsar signal of a suspected neutron star was discovered inside the Crab, supporting the theory that a supernova can leave behind these superdense, rapidly spinning balls of neutrons.

Image: A Hubble image of the Crab Nebula (credit: NASA/ESA/JPL/Arizona State Univ.)

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The Crab Nebula

Introduction

Astronomers find a star that exploded in the year 1054.

About Crab Nebula

The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus. Corresponding to a bright supernova recorded by Chinese astronomers in 1054, the nebula was observed later by English astronomer John Bevis in 1731. At an apparent magnitude of 8.4, comparable to that of the largest moon of Saturn, it is not visible to the naked eye but can be made out using binoculars under favourable conditions.

At X-ray and gamma ray energies above 30 keV, the Crab is generally the strongest persistent source in the sky, with measured flux extending to above 10 TeV. Located at a distance of about 6,500 light-years (2 kpc) from Earth, the nebula has a diameter of 11 light years (3.4 pc, corresponding to an apparent diameter of some 7 arc minutes) and expands at a rate of about 1,500 kilometers per second (0.5% c). It is part of the Perseus Arm of the Milky Way galaxy.

At the center of the nebula lies the Crab Pulsar, a neutron star 28–30 km across with a spin rate of 30.2 times per second, which emits pulses of radiation from gamma rays to radio waves. The nebula was the first astronomical object identified with a historical supernova explosion.

The nebula acts as a source of radiation for studying celestial bodies that occult it. In the 1950s and 1960s, the Sun's corona was mapped from observations of the Crab's radio waves passing through it, and in 2003, the thickness of the atmosphere of Saturn's moon Titan was measured as it blocked out X-rays from the nebula.

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