December 31, 1997

This colorful image shows the gaseous remnant of a supernova explosion as seen in X-rays. The supernova exploded approximately 2,000 years ago. The blues represent the locations of the most intense X-ray emission, while orange and red represent locations of less intense emission. The white square in the center identifies the location of the stellar remnant of the explosion, which is a spinning neutron star (also known as a pulsar).

Supernovae are the explosions of massive stars that have reached the ends of their lives. The explosions are powered by the collapse of a star's core. This collapse releases more energy in a fraction of a second than our Sun will during its entire lifetime of about 10 billion years! Most of this energy is carried away by elusive particles called neutrinos, but a small fraction of it goes into ejecting the star's outer envelope at speeds of thousands of miles per second. This ejected gas is known as a supernova remnant.

As the expanding shell of a young supernova remnant plows into the surrounding interstellar medium (i.e., the gas and dust present in the space between the stars), the gas gets heated and copious amounts of X-rays are emitted. This is what's seen in the image above.

The star's collapsed core, or pulsar (so named because in many instances we observe its radiation in pulses), has a mass comparable to that of our Sun but a size of only about a dozen miles. Thus, these are extremely compact objects. A spoonful of pulsar matter weighs more than a billion tons!

Most young pulsars spin extremely rapidly, typically about 100 times each second. In the course of billions of years, they slow down until they rotate only about once per second.

The pulsar in the above image rotates more slowly than most old pulsars, about once every 12 seconds, even though it is still very young. Why does it rotate so slowly?

Astronomers speculate that this pulsar has unusually strong magnetic fields, up to 100 trillion times the strength of the Earth's magnetic field. As the pulsar spins, its magnetic fields interact with the electrically charged particles of the surrounding supernova remnant, which creates a strong drag. This drag has slowed the pulsar's original fast rotation.

More Cool Stuff

We obtained the above image and information from the Space Sciences Pictures page of NASA's Goddard Space Flight Center:

http://pao.gsfc.nasa.gov/gsfc/spacesci/pictures/spacepic.htm

The image was taken with the "High Resolution Imager" onboard the German X-ray satellite ROSAT. For more information on ROSAT, go to:

http://heasarc.gsfc.nasa.gov/docs/rosat/rosgof.html

We have featured pulsars before in our Observations of the Week:

http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960403/ob960403.html (gamma ray pulsar)

http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960703/ob960703.html (pulsar in the Crab nebula)

As part of its Learning Technologies Project (LTP), NASA supports a number of educational Web sites that have excellent material on the space sciences:

http://observe.ivv.nasa.gov/nasa/education/edu/edudocs/topic_space.html