PEERING INTO THE HEART OF THE CRAB NEBULA

In the year 1054 A.D., Chinese astronomers were startled by the appearance of a new star, so bright that it was visible in broad daylight for several weeks. Today, the Crab Nebula is visible at the site of this violent stellar explosion. In this new image, NASA's Hubble Space Telescope has zoomed in on the center of the Crab to reveal its structure with unprecedented detail.

Located about 6,500 light-years from Earth in the direction of the constellation Taurus, the Crab Nebula is the remnant of a star that began its life with about 10 times the mass of our own Sun. Such a massive star consumes its nuclear fuel so rapidly that it lives only some 50 million years before exploding as a supernova. For the Crab star, the end came on July 4, 1054. The explosion was witnessed as a naked-eye "Guest Star" by Chinese astronomers, and is also depicted in rock paintings of Native Americans in the southwestern United States.

The Crab Nebula image was obtained by Hubble's Wide Field and Planetary Camera 2 in 1995. Images taken with five different color filters have been combined to construct this false-color picture. Resembling an abstract painting by Jackson Pollack, the image shows ragged shreds of gas that are expanding away from the explosion site at over 3 million miles per hour.

The core of the star has survived the explosion as a "pulsar," visible in the Hubble image as the lower of the two moderately bright stars to the upper left of center. The pulsar has about 1.4 times the mass of the Sun, but jammed into an object only about 10 miles in diameter. This incredible object, a "neutron star," is even more remarkable because it spins on its axis 30 times a second.

The spinning pulsar heats its surroundings, creating the ghostly diffuse bluish-green glowing gas cloud in its vicinity, including a blue arc just to the right of the neutron star.

The colorful network of filaments is the material from the outer layers of the star that was expelled during the explosion and is now expanding outward at high speed. The picture is somewhat deceptive in that the filaments appear to be close to the pulsar. In reality, the yellowish green filaments toward the bottom of the image are closer to us, and approaching at some 300 miles per second. The orange and pink filaments toward the top of the picture include material behind the pulsar, rushing away from us at similar speeds.

The various colors in the picture arise from different chemical elements in the expanding gas, including hydrogen (orange), nitrogen (red), sulfur (pink), and oxygen (green). The shades of color represent variations in the temperature and density of the gas, as well as changes in the elemental composition.

These chemical elements, some of them newly created during the evolution and explosion of the star and now blasted back into space, will eventually be incorporated into new stars and planets. Astronomers believe that the chemical elements in the Earth and even in our own bodies, such as carbon, oxygen, and iron, were made in other exploding stars billions of years ago.

K. Davidson (U. Minn.) led the research team of W. P. Blair (JHU), R. A. Fesen (Dartmouth), A. Uomoto (JHU), G. M. MacAlpine (U. Mich.), and R. B. C. Henry (U. Okla.) in the collection of the HST data. The Hubble Heritage Team created the color image from black and white data processed by Dr. Blair.

Credit: NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgments: William P. Blair (JHU)