Sereno Jacob, age 12, of Allentown, Pennsylvania, for his question:

What occurs in a supernova?

The adjective for a supernova is stupendous. For centuries, astronomers were simply stunned by the measurable dimensions of its dazzling brilliance. They assumed it to be an explosion that totally disintegrated the dynamic substance of a star. Then, some years ago, the experts were challenged to explain the newly discovered pulsar objects. And of all things, the wild little pulsar led to a fuller understanding of the stupendous supernova. As the complete story unfolds, it promises to unveil a new chapter in our knowledge of the universe.

The sudden eruption of a supernova is more brilliant than 100 billion suns and may outshine all the stars in an entire galaxy. The dramatic event occurs suddenly, as the explosion shoots shells of the star's gases outward at speeds approaching the velocity of light. Centuries after this dazzling Phase One subsides, telescopes reveal filaments of the exploding gases, still rushing outward through a vast region of space.

However, there is far more to a star than its dazzling light. For some years, astronomers have speculated about what happens to the gravity, x rays, radio and other energies when a star explodes in a supernova. Some of these theories are still no more than educated guesses. Others have been proved by radio signals from intensely energetic pulsar bodies.

Phase One shoots out dazzling shells of stellar gases.. It now seems likely that this cosmic catastrophe also disrupts all the mighty energies of the star's nuclear powerhouse. As Phase One subsides, it is suspected that its enormous gravitational force crushes what remains of the star's materials into a tight little ball, made mostly of neutrons. This core may be merely five miles wide and a thimblefull of its dense material may weigh several hundred thousand tons.

Such a neutron star exists inside huge, intense magnetic fields and gravitational forces. It rotates perhaps 20 or more times a second    broadcasting strange, pulsing radio signals clear across the galaxy. Radio telescopes detected these pulsar signals; but at first ordinary telescopes failed to detect light from the tiny objects. Then astronomers looked for them in the remains of old supernova explosions. And in several cases, there they pinpointed a pulsar neutron star    the mighty midget left behind after the original star exploded almost all its gases across the galaxy.

For 1,000 years after the razzle dazzle Phase One explosion, the remnants of a supernova continue to emit more energies than 1,000 ordinary suns. Gradually they subside through perhaps 100,000 years. In the past few years, several pulsars in old supernovas have been clocked in fine detail. And their wild whirling rotations are slowing down, fraction by tiny fraction.

Many supernovas have been observed in other galaxies.. We know that a galaxy can expect one to occur every 100 years. But we do not know what causes a star to explode in such a stupendous catastrophe. We are not sure how the dramatic story ends. But it seems likely that fragments from past supernovas span the vast reaches of space and perhaps their energies affect all the stars, planets and moons in our entire galaxy.