In the year 5346 B.C. a large mass star in the constellation of Taurus went supernova. It exploded. As this star is 2000 parsecs (6,400 light years) from Earth, the increase in brightness was not observed on planet Earth until July of 1054 A.D. All cultures that could observe Taurus recorded this event. The Chinese astronomers labeled it a guest star. It's magnitude (brightness) increased to -6. It was shining four times brighter than Venus and for a period of 23 days could be seen in daylight. At night with an absent moon, people could easily walk around without the use of torches. Unknown to all cultures at the time, they were witnessing a supernova event. The photons of light coming from this explosion took 6,400 years to reach Earth, all the while traveling at 186,000 miles per second for all those 6,400 years.
Early astronomers, like John Bevis who discovered this nebula in 1731 and Charles Messier who cataloged it as M1 in 1758, deemed it to be an unusual nebula but nothing too suspicious. For awhile it was believed to be a planetary nebula. The first photograph of it was taken in 1892 with a 20" telescope. Again it appeared unusual in comparison to other nebulae but the difference could not be explained at that time.
In 1967 Sir Anthony Hewish , Jocelyn Bell and graduate students constructed a large dipole array (a radio antenna for listening in on the universe). Almost immediately they began receiving a regular pulse signal coming from the Crab Nebula located in the constellation of Taurus. They had just discovered a Neutron Star and this star is unlike any other star in the universe.
Hewish and Bell realized that this object had to have an intense radio source, very powerful. Neutron stars spin and this one was spinning 30 times per second and sending out a radio signal like a light beacon from a light house as it sweeps by. How did this star come to be? This was a high mass star, many times the solar mass of our sun. It ejected the layered gas that surrounded its core and sent it speeding out into space at the rate of 1,800 kilometers per second. Then the exposed core of this high mass star, estimated to be about 6,000,000 kilometers in diameter, collapsed by its own gravity into a star of 10 kilometers in diameter. Think about it. All of the matter in the original core crushed and compacted into an area 10 kilometers in diameter. Super, super dense. It is estimated that a teaspoon of matter from this star would weigh 100,000,000 tons and a school bus size chunk would out weigh the Earth. It is safe to assume that the fabric of space is severely dimpled in this region. The gas ejected has now expanded out to about 4 parsecs (12.8 light years) or 75 trillion miles and continues to expand.
Now that astronomers know what to look for, many Neutron Stars have been discovered since Hewish and Bell. It would not benefit Earth to be 93,000,000 miles from this Neutron Star as Earth would be engulfed in synchrotron radiation. Sounds bad doesn't it. It is, especially for soft tissue human beings. X-rays, cosmic radiation and all manner of events would eradicate all life on Earth not to mention the planet itself. We are safely 6,400 light years from this object but it is believed that the Crab Nebula is a source of the primary cosmic rays that continually bombard Earth. Even after 7,350 years, we feel the effects of this supernova event and will continue to do so for thousands of years into the future.
The universe is elegant and complex. It is estimated that there are approximately 100,000 Neutron Stars in the Milky Way galaxy. Models of the structure of Neutron Stars indicate that the crust may be only a few centimeters thick, under which is a crystalline crust about one kilometer in depth. Beneath the latter the material is thought to act like a superfluid of neutrons all the way to the core.
We regulary observe the Crab Nebula with the observatory's telescopes and delight in explaining this object to visitors. We always point out to our guest that they are observing a supernova remnant, a star that exploded 7,350 years ago.