M1 (Crab Nebula)

Constellation: Taurus

Distance: 6500 Light Years

Like the Veil Nebula, M1 (the Crab Nebula) is a remnant of a supernova that occurred in our own galaxy, the Milky Way, and is the most famous and studied supernova remnant.  A supernova occurs when a supergiant star runs out of nuclear fuel at the end of its life.  As the heat and pressure in the star’s core diminish, the outer layers lose their support and collapse under their own gravity.  The collapse then rebounds in an enormous explosion.  Astronomers estimate that a supernova occurs in the Milky Way 2 to 3 times every 100 years.  However, because interstellar dust obscures so much of the view of our own galaxy, these supernovae are rarely observed (most observed supernovae occur in other galaxies).  The last was observed by Johannes Kepler in 1604.

The supernova that resulted in M1 was observed and documented by Chinese astronomers in the year 1054 (they termed it a “guest” star).  Its brightness was 4-6 times brighter than Venus, comparable to the full moon, and visible in the daytime sky for 23 days.  The resultant gaseous nebula is one of the brightest supernova remnants in the sky, but detection of it required the advent of the telescope, with the first observation occurring  in 1731.  Charles Messier placed it as his first entry in his list of deep sky objects that may be mistaken for comets (the Messier Catalog, hence the designation M1) in 1758.  In 1844 Lord Rosse coined it the “Crab Nebula” because its filaments reminded him of crab legs.

M1 currently measures about 10 light years across in size, and is expanding at over 1500 kilometers per second. It is mostly composed of gaseous and filamentary material expelled from the explosion,   mostly ionized hydrogen glowing red, as well as some other elements including oxygen glowing  blue.  At its center lurks a neutron star, the remaining core of the star that exploded (it can be seen in the image, the fainter of the 2 stars at the center of the nebula).  This neutron star is VERY dense, about 1.4 solar masses contained in a space about 28 kilometers wide, has a powerful magnetic field and is spinning rapidly – 30 times per second -  with the ejected radiation sweeping over earth like light from a lighthouse, earning these types of stars the designation “pulsars”.