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Melinda Portero, age 17, of Shreveport, Louisiana, for her question:

What causes those black holes in space?

The teeming majority of normal stars are tabulated in predictable classes. But the recently discovered pulsars do not perform like average stars. This cosmic mystery presented numerous problems, yet astronomers have solved most of it in the past couple of years. Their research hinged on two recent theories. One suggested tiny neutron stars, densely packed with nuclei particles. The other suggested fields of intense gravitation, strong enough to create black holes, somewhat like isolated prisons in the universe.

Space probes reported that the outer realms are filled with thin gases charged with dynamic energies. This filmy plasma appears to fill the universe, concentrating in dense gobs to form the stars. There seemed no room for empty black holes in this inter related universe. Then strange radio signals were detected from mysterious pulsars. Apparently they are those predicted neutron stars, energetic midgets, just a few miles wide and perhaps as massive as our sun.

Scientists suspected that pulsars could be the collapsed cores of exploded stars and telescopes pinpointed several of them in the remnants of old supernovas. Tabulations indicate that extra massive stars tend to burst apart in supernova explosions. And mass is related to gravity. As a cosmic force, gravitation is rather weak. But its persistent pull is exerted in every speck of matter and it spans out through the infinite universe. It patiently contracts a thin cosmic cloud and exerts its pressure until the crowded particles ignite the nuclear furnace of a star. It holds this mass together as the nuclear fuel is consumed to ashes.

This is how gravitation governs the life of an average star, with a mass perhaps ten times greater or smaller than our sun's. Apparently this pattern changes in more massive stars. After some of the fuel is consumed, the gravitational energy in the outer shell collapses. The seething outer gases explode in a stupendous supernova: The collapsed gravitation concentrates its enormous force in the central core, crushing it into a massive midget. This dense neutron star may emit pulsar radio signals as it rotates on its axis perhaps 30 times per second.

As we know, gravity spreads out from its source, diminishing with distance. Its force is counteracted by the spinning of rotating or orbiting bodies. The gravitational field around a massive neutron star may be so intense that no particle of matter can escape or enter. It may be forceful enough to create a barrier to the passage of light, magnetism and other energies that normally spread through the universe. Such an intense gravitational field could create an isolated black hole in space.

Some of the gravitational field may be cancelled by the fast rotation of an imprisoned pulsar. Gravity diminishes with distance and the strength of the field gets stronger toward the center. Perhaps these and other factors make it possible for radio and light from certain pulsars to escape and reach the earth. So maybe those black holes are not quite as isolated from the rest of the universe as we thought they were. We can expect more details when scientists have had another couple of years or so to probe the problem.

 

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