A supernova is the massive explosion of a star, and is one of the most violent events in the Universe (Hall 3913). In a single deluge, a massive star may blow itself to pieces and release as much energy as an entire galaxy for a brief time. There are two types of supernovae. Type I involves stars of about 1 solar-mass, like our Sun, that would gently blow off about 50 percent of their mass into space. Gravity would pull the star’s remaining mass back, forming a white dwarf–a tight sphere about the size of Earth (Shubinski 70).
Type II covers stars of 8 solar-masses or greater and end their lives differently. As these stars run out of thermonuclear fuel and can no longer sustain itself against the inward pull of its own gravity, their cores collapse under the force of gravity only to rebound in tremendous explosions. The outer layers collapse as well, but when they encounter the extremely hard, rigid, collapse core, they bounce off. An immense cloud of glowing gas rushes outward and some of the nebulae visible in small telescopes are these dispersed outer layers of the collapsed star.
Gravity compresses whatever mass is not blown into space into a sphere only a few miles in diameter. The matter in this stellar remnant is crushed until it is packed as tightly as an atom’s nucleus, which finally stops the collapse. This object, known as a neutron star, spins at a tremendous speed (Cowen 87). Six thousand light-years away in the constellation Taurus lays an extraordinary object known as the Crab Nebula which is the tattered remains of a star that went supernova in the year 1054 (Talcott 42).
It is a maelstrom of high-energy particles and radiation powered by a pulsar – the ultra dense, rapidly spinning core of the exploded star that lies at the heart of the nebula. Astronomers have intently observed this supernova remnant for over two centuries, making it one of the best studied objects in the sky. Asian astronomers carefully documented the supernova, some Native Americans may have drawn it but no evidence clearly revealed that the supernova was seen in Europe (Cowen 87) even though the event was visible in the skies for almost two years.
According to Chinese chroniclers, the Crab supernova remained visible in broad daylight for more than three weeks. One reason was its relative proximity, a mere 6,300 light-years away (Seronik 52). This strange “guest star” entranced the Chinese. Astrological interpretations drove their study of the stars. Being an astrologer in the court of the Sung emperor was a deadly serious business. They predicted solar and lunar eclipses, and noted many guest stars. The guest star of 1054, however, received special attention (Shubinski 70).
Chinese astronomers first observed the guest star near the star T’ien-kuan, known to us as Zeta Tauri, a star representing the tip of one of Taurus the Bull’s horns. The new star that had split the heavens open has brought great anxiety to the emperor. Astrologer Yang Wei-te appeared before the emperor with this report: The guest star “does not trespass against Pi, the lunar mansion in Taurus, and its brightness is full meaning that there is a person of great wisdom and virtue in the country” (Shubinski 70).
The guest star first appeared on July 4, 1054, and faded from view April 17, 1056. Except for these few records, it has also faded from human memory for the next seven centuries. In the spring of 1758, Frenchman Charles Messier was hunting for a comet near the star Zeta Tauri, Messier thought he had found a new comet, but the object refused to move. Messier decided to start a catalog of these “non-comets,” and he made this object in Taurus the first on his list – M1. Although this object became the first in Messier’s now famous catalog, he was not the first to observe it.
That honor goes to Englishman John Bevis, who glimpsed this faint speck of light in 1731. Messier generously acknowledged the discovery by Bevis in a later edition of the catalog. In 1844, William Parsons, third earl of Rosse, who excelled at drawing what he saw in the eyepiece, observed M1 using his reflecting telescope with a 36-inch (91 centimeters) mirror and made some notes: “We see resolvable filaments singularly disposed, springing principally from its southern extremity, and not, as is usual in clusters, irregularly in all directions.
” The drawing of M1 looked rather like a beach crab, and the object soon came to be known as the Crab Nebula (Shubinski 70). At the turn of the 20th century, Vesto M. Slipher, the late director of Lowell Observatory in Flagstaff, Arizona found that M1’s spectral lines indicated the nebula was expanding fast. Today, we know the gas travels outward at 3. 3 million mph (5. 4 million kilometers per hour) (Shubinski 70). Images taken decades apart show the Crab Nebula changing over time.
Further studies placed the Crab about 6,000 light-years away. It engulfs an area of space greater than 10 light-years across. Studies of the Crab Nebula show that it is expanding with the enormous cloud of gas looking like it had been flung outward from a central point. Modern stellar evolution theory has provided a reason for this: the “guest stars” were the final acts in the lives of a massive star. These stars end their lives as supernovae, massive explosions that blast the stars’ outer layers into space.For a short time they can rival the brightness of a small galaxy; later, like a dying coal in a fire, they fade away (Hall 3913).
Cowen, R. “Shedding Light on an Ancient Supernova. ” Science News 7 August 1999: 87. Hall, Jeffrey. “Supernova. ” Gale Encyclopedia of Science. 3rd ed. 2004. Eds. Lee Lemer and Brenda Lemer. Vol. 3: p. 3913. Seronik, Gary. “The Crab Nebula. ” Sky & Telescope February 2007: 52. Shubinski, Raymond. “All About the Crab Nebula. ” Astronomy January 2007: 70. Talcott, Richard. “Inside the Crab Nebula. ” Astronomy December 1994: 42.