Crab Nebula
8.4 may
6 ' x 4'
6300 Lj
1731
M 1 • NGC 1952 Sh 2-244 •
The Crab Nebula is both a supernova remnant and pulsar wind nebula in the constellation Taurus and is guided in the Messier Catalog as M 1 and in the New General Catalogue as NGC 1952.
Observation history
A monk in Flanders fell on April 11, 1054 a " bright disk in the afternoon ", which - as we now know - the Erstbeobachtung the light from a supernova explosion was that was so on April 11, 1054 for the first time perceived on Earth. Better known is that on July 4, 1054, a Chinese court astronomer discovered a star that was visible during the day next to the sun. In North America, provide drawings represent this supernova explosion, from which the mist was then. A total of 13 previously timely historical sources could be found for this celestial event of 1054.
The nebulous remnant was discovered in 1731 by John Bevis, and regardless of by Charles Messier on August 28, 1758 - this discovery was the trigger for Messier to create Messier's catalog in which the Crab Nebula is classified as the first object M 1. The name was coined in 1844 by the Crab Nebula Lord Rosse, who with his large telescope watching the fog in detail and also recorded. Based on the similarity of the filaments with cancer legs, he noted: "He looks like a cancer. " In 1948 the fog be identified with the radio source Taurus A and 1964 with the X-ray source Taurus X -1. In 1968/69 was the pulsar PSR B0531 21 are identified in the optical domain as the central star of the Crab Nebula.
When they had received the first photographs in the early 20th century, it turned out that the fog is expanding. By returning calculation this expansion you unlocked a supernova explosion about 900 years ago. The supernova was thus already about 7200 years ago - or based on today about 7260 years ago - since the light as an information carrier needs a certain time to reach Earth. However, it has become customary that one dated to the time of the sighting of a supernova.
Physical Properties
In visible light, the Crab Nebula can be seen as an oval body, which consists of wide filaments. This case is about 6 arcminutes long and 4 arcminutes wide and surrounds the diffuse blue region in the center of the body. The filaments are remains of the original atmosphere of the star and contain mostly ionized helium and hydrogen and also carbon, oxygen, nitrogen, iron, neon, and sulfur. The temperature of the filaments is usually between 11,000 K and 18,000 K and its density is about 1,300 particles per cm ³.
1953 suggested Iosef Shklovsky ago to explain the blue glow of the Centre by synchrotron radiation. This is the radiation which is emitted when electrons, which move at at least half the speed of light, are forced through a magnetic field to a circular path. Three years later this theory was confirmed by observations. 1960 was it concluded that the magnetic field of about 108 Tesla resulted from a neutron star in the center of the nebula.
The Crab Nebula stretches currently at a speed of 1500 km / s, and images that were made several years ago, confirm this. If we compare the extent and redshift, one can determine the distance. Thanks to modern observations one has determined a distance of about 6,300 light years.
Extrapolating the expansion back, you get a date for the formation of the nebula, which refers to several decades after 1054. It seems that the fog may have extended accelerated. It is believed that the energy required for the acceleration is derived from the pulsar, the magnetic field increased, and so the filaments are more away from the center.
It is necessary to estimate the mass of the nebula in order to determine the mass of the original star, which existed before the supernova. Estimates for the mass of the filaments of the Crab Nebula range from 1-5 solar masses.
Central star
In the center of the Crab Nebula are two faint stars. One of them is responsible for the formation of the nebula. 1942 Rudolph Minkowski realized that the Crab Nebula has an extremely unusual spectrum. It was found in the region around the star in 1949 a strong source of radio waves to X-rays in 1963, and it was one of the brightest objects in the field of gamma radiation in 1967. 1968, it was found that the radiation is emitted in pulses.
Pulsars are the sources of powerful electromagnetic radiation that are repeatedly emitted in short and extremely regular intervals in the second. 1967 was a big mystery how such a thing could be explained. The team that discovered the pulsar, went himself from a signal of an advanced civilization. Today we know that it pulsars is rapidly rotating neutron stars whose strong magnetic field is concentrated in narrow beams.
It is believed that the pulsar has a diameter of 28 up to 30 km. It transmits every 33 milliseconds radiation pulses which are distributed over the entire electromagnetic spectrum, from radio to X-radiation. As with all pulsars takes its period slowly. Sometimes the pulsar shows temporal disturbances in its period. It is believed that they result from a sudden rearrangement of the material in the neutron star. The energy lost to the pulsar, while it is slower, is enormous. Only the synchrotron has a luminosity that is about 75,000 times stronger than the sun.
Due to the extreme amount of energy emitted by the pulsar, creates an extremely dynamic region in the center of the Crab Nebula. While most changes of astronomical objects happen so slowly that you can perceive it only after many years, the interior of the Crab Nebula is changed within a few days. The areas with the greatest changes in the inner part of the nebula are at the point where the polar jets of the pulsar collide with the surrounding material, forming a shock wave. Together with the equatorial wind, they appear as a series of tuft -like structures that grow out steep, brighten and then fade when she and away - inside move from the pulsar in the fog.
Original star
The Crab Nebula was created from the supernova explosion of a star. For theoretical models of supernova explosions, it is concluded that the star must have had a mass of 8-12 solar masses. It is believed that stars that have less than 8 solar masses are too small to explode in a supernova and end their lives with the creation of a planetary nebula, while stars with more than 12 solar masses a mist with a different chemical composition than the form the Crab Nebula.
An unsolved problem in the Crab Nebula is that the mass of the pulsar and the nebula is composed smaller than that of the original star and you do not know where the missing mass remains. To estimate the mass of the nebula, it measures the amount of light emitted and the mass calculated at a given temperature and density of the fog. This yields an interval of 1-5 solar masses, while 2-3 solar masses is the most accepted value. The neutron star mass is estimated to be 1.4 to 2 solar masses.
A prevailing theory is that the missing mass was carried away from the original Star by the stellar wind before the supernova explosion. However, this would lead to a shell around the Crab Nebula. Although we had been looking for this sheath in different wavelengths, so far none have been found.
Transit of solar system bodies
The Crab Nebula is about 1.5 ° from the ecliptic plane of the Earth's orbit around the sun. This means that the Moon and planets can sometimes cross this seemingly fog in the sky or strip. The sun itself, however, does not pass through the mist, while its corona. Such events help to explore the fog and objects in front of the mist better by examining how changes the radiation of the nebula.
Moon transits were used to find the sources of X-rays in the fog. Before we had satellites such as the Chandra X - Ray Observatory, which were able to observe the X-ray, X-ray observations usually had a low resolution. However, when the moon moves in front of the fog, you can use the changes in brightness of the nebula to produce maps of the X-ray emission of the nebula. As had been observed for the first time X-rays in the Crab Nebula, the moon was, as he brushed the nebulae in the sky, used to identify the exact position of the X-rays.
The solar corona crosses the Crab Nebula every June. Due to changes in the radio waves of the Crab Nebula, you can deduce the density and structure of the solar corona. The first observations revealed that the solar corona is much more extensive than previously believed, later observations showed that it has significant density fluctuations.
Very rarely the Saturn crosses the fog. Its transit in 2003 was the first since 1296, the next will be in 2267. Using the Chandra X - Ray Observatory of Saturn 's moon Titan was examined more closely. It turned out that even X-rays emitted by titanium. The reason for this is in the absorption of X-rays in its atmosphere. This gave a value of 880 km for the thickness of Titans atmosphere. The transit of Saturn itself could not be observed because Chandra at the time the Van Allen belts crossed.