Crab Nebula Essay, Research Paper

The Crab Nebula

The Crab Nebula is the nearest, most conspicuous and appealing supernova remnant. In 1054, a star in the constellation of Taurus exploded in a supernova (the violent death of a star) so bright that it dominated the evening sky for more than a year. (History of the Crab Nebula) The nebula consists of the material ejected in the supernova explosion, which spreads over a volume of 10 light years in diameter, and is still expanding at a velocity of 1,800 km/sec. (Messier Object 1)

Discovered as a “guest star,” by Chinese astronomers on July 4, 1054 A.D., it was four to six times brighter than Venus. Although it is nearly 6500 light years away and has a diameter of 6 light years, it was visible in daylight for 23 days and 653 days to the naked eye at night. The “Chinese astronomers described the star as having pointed rays in four directions and a reddish-white color.” (Messier Object 1)

The Anasazi Indians in Arizona and New Mexico may have also seen the event and drawn pictures of it. Three pictographs have been found, on in a cave at White Mesa and on a wall of Navajo Canyon and the Chaco Canyon national park. (Messier Object 1) The drawings show a large star with a crescent moon nearby. “Scientists have calculated that on the morning of July 4, 1054, the Moon was located 2 degrees north of the Crab nebula’s current position.” (History of the Crab Nebula)

The supernova was discovered again more than 600 years later, in 1731, by English physicist and amateur astronomer, John Bevis. Then in 1758, while searching for Comets, Charles Messier spotted the nebula, noting that it had no apparent proper motion. The nebula became the first entry (September 12, 1758) in his famous “Catalogue of Nebulae and Star Clusters” which was first published in 1774. In 1844, Lord Rosse named the nebula the “Crab” because its tentacle-like structure resembled the legs of the crustacean. In 1892, the first photo was taken with a 20-inch telescope. In 1913-15, Vesto Slipher found that the spectral emission lines were split. Because of the Doppler Shift, parts of the nebula were approaching us (blue shifted lines) and the others were receding from us (red shifted lines). In 1919, R.F. Sanford discovered that the nebula emits light do to two reasons. “First, a reddish component which forms a chaotic web of bright filaments, which has an emission line spectrum like that of diffuse gaseous (or planetary) nebulae. Second a bluish diffuse background which has a continuous spectrum and consists of highly polarized `synchrotron radiation’, which is emitted by high-energy (fast moving) electrons in a strong magnetic field.” (Messier Object 1)

In 1942, Walter Baade discovered a prominent star near the nebula’s center that might have been related to its origin. Six years later, the Crab nebula was identified as a powerful source of radio waves, and in 1964, a high-altitude rocket detected X-ray energy from the nebula. It was a powerful source of radiation, but scientists were unsure about its origin. On November 9, 1968, astronomers of the Arecibo Observatory in Puerto Rico discovered an object in the nebula’s center–it was Baad’s prominent star, a small and dense star composed almost entirely of neutrons, that propels charged particles outwards and spins magnetic fields. Called the Crab pulsar, the fastest and most energetic pulsar, it emitted bursts of radio waves 30 times per second. However, because the pulsars are actually slowing down, the Nebula is also losing energy.

The Crab Nebula has been a major key in “understanding the death of massive stars and their material afterwards.” (Voyages Through the Universe) I think that by studying the crab nebula and other supernovas, astronomers are able to understand what happens to exploding stars. For example, of the explosion was only 50 light years away from the Earth, astronomers believe that all living things on Earth would have died because of radiation.