M1, The Crab Nebula

In 1054 AD, the Anasazi Native Americans noticed a new star in the constellation of Taurus. It was initially so bright that they made note of it in cave paintings. Although once visible during daylight hours, it has long since faded from sight. However, nearly a millennium later we can turn robotic eyes to this spot to reexamine a past stellar mystery. The result is the picture above, taken within a few hundred miles of the original Anasazi discovery.

When stars die

Ironically, the “new star” detected by the Anasazi was actually the violent end of an old star. When a massive star reaches the end of its life, it runs out of light elements to fuse. Since the energy produced by fusion is necessary to counteract the inward gravitational pull of a star, its absence is catastrophic. Acted upon only by gravity, the stellar core collapses upon itself. The outer layers of the star initially rush inwards, and then explode outwards due to tremendous pressure near the star’s center. For a few weeks, the light from this explosion outshines anything else in its galaxy. This explosion is called a supernova, and is what the Anasazi witnessed.

The image above (known as the Crab Nebula), is the aftermath of this explosion, and is thus referred to as a supernova remnant. The red and green filaments in the image are ejected stellar material. The red material consists of hydrogen, while the green filaments are composed of oxygen. The light given off by this material is called fluorescence; it occurs as photons are emitted from electrons switching between energy states. The central blue region, however, is an entirely different light known as synchrotron radiation. Such light is emitted by electrons because they are gyrating around the Crab’s strong magnetic field at near-light speeds.

The Crab Pulsar

Slightly left of and below the center of the nebula is a pair of close, bright stars. The lower right one is the crab pulsar. It is the remaining core of the exploded star. Next to a black hole, pulsars are one of the densest known objects in the universe. At a mere 10 kilometers in diameter, the Crab Pulsar is so dense that one tablespoon of it would weigh 100 million tons. It is also spinning at a rate of 30 revolutions per second. Its ferocious magnetic field forces radiation out of its north and south magnetic poles, causing a pulse when the rotating beam sweeps past earth.