Magazine article Science News

Pulsar Hints at Supernova Asymmetry

Magazine article Science News

Pulsar Hints at Supernova Asymmetry

Article excerpt

The geometry of a fanshaped supernova remnant called G5.4-1.2 has fascinated radio astronomers for nearly a decade: Its structure resembles a crossbow launching an arrow. In 1985, Australian researchers linked a nebula sitting at the tip of the arrow with a nearby pulsar--a rapidly rotating, radio-emitting neutron star.

Now, two radio astronomers in the United States have determined that the pulsar lies within the arrow, where its energetic emissions likely power the nebula's radio broadcasts.

Using the Very Large Array radio telescope near Socorro, N.M., the U.S. team also traced an elongated trail of radio signals leading from the crossbow to the arrow. These suggest that the pulsar was indeed shot out of the supernova remnant. By estamating the pulsar's age (about 15,000 years) and the distance it seems to have traveled from the crossbow to the arrow, the scientists infer that this relatively youthful pulsar races along at an astonishing 2,300 kilometers per second, or 0.5 percent of the speed of light. This would make it by far the fastest neutron star ever found.

The pulsar, a Milky Way resident known as PSR 1757-24, appears to move so rapidly that it has overtaken the expanding shell of debris created at its birth during the supernova explosion. Pulsars form as gravity squeezes the remains of a massive, exploded star. Researchers often think of this squeezing as s symmetric process in which all sides of the dying star experience the same amount of compression.

But the speed and direction of PSR 1757-24 suggest that the compression may have occurred asymmetrically -- for example, with more material raining onto the shrinking star from above than from below. …

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