Shadow of a Star: The Neutrino Story of Supernova 1987A

  • Alfred K. Mann
W. H. Freeman: 1997. Pp.210 $22.95, £16.95<)

Supernova 1987A is the most famous supernova of them all. There are two main reasons: it was the first supernova visible to the naked eye for some four centuries and it was the first ever to be detected by its neutrino flux. In fact the neutrinos were registered around three hours ahead of the first optical detection – not surprising really, because the neutrinos are produced deep down within the star that became a supernova and travel straight out from there. The light from the event, however, is not emitted until the shock wave reaches the surface of the precursor star; the passage from the deep interior took three hours in the case of 1987A. In all, 20 neutrinos were collected at the Kamioka and the Lake Erie installations, carrying between them about 10−10 joules, or roughly one part in 1056 of the energy released in the collapse of the precursor to a neutron star.

What a fantastic success; and the experiment had not even been planned that way. As Alfred K. Mann explains in his delightful book, the apparatus was designed to detect neutrinos emitted during the putative decay of protons. One tends to think of the proton as a stable constituent of the Universe, but theory has it that even protons do not last forever, with a lifetime possibly as short as 1030 years. In the event, this turned out to be an underestimate, and so the apparatus was left with nothing to look at. Mann tells the story of how he and his colleagues modified their experiment, what incredible care had to be taken with their procedures and how they made their great coup just months after the final adjustments. Those 20 neutrinos are probably the most important particles in the history of astrophysics, and will continue to be so until someone actually catches a magnetic monopole. But the biggest surprise of all is that nobody on the Kamiokande team has yet been awarded a Nobel prize. If ever recognition was overdue, here is a prime example.

Mann's book is compact, and focused on one essential aspect of astrophysics. By contrast, James B. Kaler's book is large and wide-ranging, although a little small for a coffee table. It is concerned with great theories, and all astrophysical life is there. The illustra-tions vie with each other in magnificence. Inevitably, the most striking of them are pictures of diffuse objects such as the Eagle Nebula, a region of active star formation in interstellar space, and of the Helix Nebula, a planetary nebula. Both photographs were taken with the Hubble Space Telescope – where would we be without it?

Kaler has organized his text around the pictures to trace the sequence of events whereby material in space takes its various known forms: how we can observe it and what we need to do to understand its physical and dynamical evolution. It is a bold scheme, but perhaps the author asks too much of his audience. It is hard to expect readers to spend great lengths of time ploughing through, say, the ins and outs of molecular spectroscopy when they could be feasting their eyes on all the gorgeous colour pictures. And quite right, too: as the Bard says, in Love's Labour's Lost: “Small have continual plodders ever won save base authority from others’ books.”

Both Kaler's and Mann's books illustrate one great eternal truth. If an author knows what he wants to say then his text is easy to read. When Kaler deals with the subject of planetary nebulae or when Mann describes his experiences with Kamiokande, then the reader is carried along willy-nilly, like a yacht with a following wind. But the going gets much rougher when they write about subjects outside their ken, as witness Kaler's strange views on barred galaxies or on synchroton radiation. And Mann, for all his wisdom, delivers himself of the following insight: “the supernova phenomenon… is an event with far more violence than humans can produce, but unlike much of our violence it is not mindless”. Something inside one boggles. A learned rabbi once told me that no human construct should ever be expected to be perfect, and that only the Almighty can achieve perfection. He was probably right.