Daniel John, age 13, of Duluth, Minnesota, for his question:

 Do we know how stars are formed?

This conundrum is a big problem for the astrophysicists and the stellar astronomers. A star has an immense life span and we cannot watch it progress from birth to death. The experts, however, have used masses of indirect evidence to figure out the most likely answers.

We cannot explain every detail that occurs in the formation of a star but we have a general idea. It is based on masses of data gathered with the help of telescopes and spectroscopes. Our knowledge of nuclear physics also helps, for stars are cosmic powerhouses of nuclear activity, In addition to all this data, researchers in recent years have also had the help of the radio telescope. This instrument gathers radio waves of cosmic energy from afar. It has corroborated the findings of the big telescopes and also added a new range of its own to our picture of the cosmos.

We know that our star studded Galaxy is strewn with immense clouds of hydrogen gas and cosmic dust. Since stars are more or less concentrated balls of these materials.. it seemed logical to regard such clouds as stellar breeding grounds. Evidence from both telescopes and radio telescopes has supported this idea. Surveys of the vast hydrogen nebulae in the constellations Orion, Taurus and Perseus reveal pockets of concentrated materials. They appear to be developing stellar eggs in cosmic nests of filmy hydrogen.

In such concentrated pockets, we can expect the gaseous particles to collide more often than those in the thinner parts of the cloud. With time and more time, colliding particles stick together and form larger fragments. Radio surveys have pinpointed a wide range of different materials in the stellar embryos. The dust fragments contain heavy atoms such as iron and nickel, compounds such as methane and ammonia and crystals of frozen water.

This process of building larger from smaller bits of matter seems reasonable. It seems logical to expect the same process to continue. But we are not certain how the dusty fragments congeal to form a massive, unborn star. One theory suggests that they are pushed together by the weak, slow acting pressure of star light. In any case, the star embryo takes eons to congeal. Gravitation and other cosmic forces cause the dusty pocket to shrink and become dense. It reaches a critical stage and the next operation occurs in perhaps a mere 100,000 earth years. It is ignited by its enormous pressure and heat and the infant star is born in a blaze of seething nuclear activity.

The basic ingredient in star formation is hydrogen gas. Radio images reveal the hydrogen atoms in nearby stars as sharp, narrow spikes. In cosmic clouds, the hydrogen image may be a blurred hump. Such distortions reveal the structure and turbulence of a cosmic cloud. The velocities of the streaming gases vary from 1,000 to 100,000 miles per hour and every 10 million years or so our galactic cloud collides with another one and gains fresh energy. If it has wild turbulence plus high heat and pressure, it is likely to form a batch of new stars.