M1 - The Crab Nebula
Introduction
The Crab nebula is a supernova rementant that was discovered and recorded by Chinese Astronomers in 1054 when the central star went supernova creating a large explosion. The nebula has been expanding ever since and is now one of the easiest objects to observe with amatuer type equipment.
The Central Star
The central star in the crab nebula is a so called neutron star. As the star collapsed before going supernova it gathered up rotational speed due to conservation of angular momentum. This means that the star is now spinning with a period of some 33ms(one of the fastest pulsars known), this can be seen by observing the pulse interval time of the radio emmission(This type of star is also be known as a radio pulsar). The star emits in all wavelengths but has very strong emmission in the UV and X-ray due to synchotron radiation. Synchotron radiation is caused by electrons orbiting the magnetic field of the pulsar. Neutron stars are very, very dense with nuclear densities of up to 1x10^18 kg/m^3 the mass of the neutron star in crab is estimated to be between 1.5-2 solar masses and about 20-30km across.
Position
The Crab nebula is located in the constelation Taurus(click on picture for larger map). Using observations of the pulsation rate and arrival time for the radio frequency pulses we can place a distance to the central pulsar of around 1800pc (6300ly). Using photographs from different ages we can observe a transverse expansion of the nebula of ~1800km/s. The nebula is expanding so fast we can actually observe the movement across the sky over a short period of only a few years.
Structure
The outer shape of the crab nebula seems to be a kind of prolate spheroid almost like a lemon, this may be because not all the material ejected was accellerated uniformly. Observations of the central area near the pulsar show a diffuse blue thought to be caused by the synchotron radiation discussed earlier. A Chandra observation of the crab pulsar shows the high energy jets and emission in the torus surrounding the pulsar(see paper here for more details)
(Credit: X-ray: NASA/CXC/ASU/J.Hester et al.; Optical: NASA/ESA/ASU/J.Hester & A.Loll; Infrared: NASA/JPL-Caltech/Univ. Minn./R.Gehrz)