What a wonder is the universe, and what a privilege it is to peer into its depths-to witness events removed from us by billions of lights years of space and time. The Hubble Space Telescope (HST) and the photos which comprise Hubble: The Mirror on the Universe are a testament to both the wondrous technology that equips this image-collecting satellite and the majesty of a universe we are now, more than ever, capable of seeing and understanding. What is there to see and marvel at? The sheer vastness of the cosmos, the magnitude of the forces coursing through it; forces that trigger reactions powerful enough to cause the formation of multitudes of stars; forces that tear apart whole galaxies as the gravitational pull of larger neighbor galaxies effects mergers' or takeovers'; forces that bring about the destruction of giant stars; forces causing either the collapse or the expansion of huge portions of space; forces producing phenoma of awesome beauty which we are now able to delight in thanks to the light-gathering mirror of the HST, perfectly positioned to observe through "the pristine clarity of airless space."
What do these images help us to understand? Nothing less than the evolution of the cosmos. Since it has been calculated that the universe is thirteen to fifteen billion years old, and since the HST is able to collect light reaching it from a distance of 13 billion light years away, the resulting images relate events "close to the time when we believe the universe was born." Other images of objects-stars and star clusters, nebulae and galaxies-at varying distances from us, enable astronomers and cosmologists to study the various chronologically linked stages of stellar and galactic activity-to learn about the present by observing the past unfolding of the universe.
Hubble, the Mirror on the Universe isn't just a collection of beautiful and fascinating images-it's an intelligently organized book, appropriate for most readers (though the text may challenge preadolescents), that manages to construct a big picture-both of the Big Bang and of the universe's ultimate fate-out of the various, and now visible, aspects and stages of cosmic life.
The sections or chapters in the Hubble follow in logical order: The first section deals with the birth of stars, describing the composition of interstellar medium, the clouds of gas and dust which contain the raw material necessary for star formation. The second section explains stellar life cycles, and covers the demise of different types of stars. Interestingly, the self-destruction of stellar supergiants leads either to the formation of black holes or the release, into the surrounding medium, of elements (heavier than iron) which are vital for the formation of new stars. This supernova event is itself a crucial trigger; it initiates a disturbance in the interstellar medium and jump-starts the process of nebular collapse, which in time results in the dense, gravity-cased clump of matter, the core of which is the protostar or the "star in embryo". The third section the Hubble explains the three basic types of galaxies. We are also told that galaxies are always on the move, acquiring a particular shape or losing their original one, pulled apart as they are gravitationally overpowered by the greater mass of a companion galaxy. Galactic collisions or mergers also cause the massive interstellar disturbance that leads to star formation. Why do galaxies travel in numbers and have the tendency to merge with others into clusters and superclusters? In the fourth section, " The Expansive Universe", we read about the scientifically perplexing dark matter-which cannot be seen but exerts sufficient gravitational force to hold entire clusters of galaxies together as they hurl through space. It is this dark matter that holds the key to predicting the ultimate fate of the universe. Will there be enough dark matter to rein in the expansion of the universe or will the universe continue expanding until all the objects in it are strewn too far apart to interact. New starts wouldn't be born, the old would simply die, and eventually all the galaxies would fade away.
Fascinating and informative, I recommend Hubble for young and older readers alike.