Grand Puzzle What Triggers the Formation of Stars

Star formation is a very important part of modern astrophysics. One of the great quests is to understand how the rate of star formation in the Universe has changed from the very early Universe to the present epoch. This is still a controversial subject. It does seem clear that the rate at which stars formed in the Universe was much higher 6-8 billion years ago, mostly in the more massive galaxies, than it is now. Just how large the star formation rate was at even earlier times is still uncertain, partly because of the effects of dusty masks in these young galaxies that are observed at early epochs.

One of the difficulties in studying star formation rates is that we do not understand star formation itself! The reader may be alarmed at this, but our knowledge of how gas is triggered to form stars is still very rudimentary. For example, the Large Magellanic Cloud, so beautifully seen from South African and Australian skies, is rapidly converting its gas into stars, but we do not really understand why this is happening.

Why does the Large Magellanic Cloud show a magnificent pattern of huge gas bubbles everywhere (Figure 170) but no regular spiral pattern? Star formation here could be stochastic (random). As has been emphasized at our international conferences on galaxies held in South Africa, we really do not understand what kick-starts the star formation process in this breed of galaxy.

There does indeed seem to be an element of unpredictability. One of the major thrusts for morphology in the new millennium will be to understand better how stars form. Our understanding needs much enlightenment; we want to know enough so as to begin with the observed infrared backbones of galaxies and predict what the optical images would look like: star formation is a vital link in this process.

If one could make this prediction, then one would understand the Hubble sequence. At the present time, we do not understand star formation and our knowledge of spiral structure is still rudimentary. Our understanding of galaxy morphology is thus truly precarious.

But there is no need for despair. In 1835, the philosopher Auguste Comte remarked about the stars:

We see how we may determine their forms, their distances, their bulk, their motions, but we can never know anything of their chemical structure or their mineralogical structure

(emphasis, ours)

How insights do change. It was in the same period that Joseph Fraunhofer passed sunlight through a prism, revealing its spectrum, and today we do know a lot about the chemical compositions of stars!

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