Active Galactic Nuclei

  • Julian H. Krolik
Princeton University Press: 1999. 598pp $39.50, £23.95 (pbk)

A significant minority of galaxies possess a monster at their centre. These objects, known as active galactic nuclei (AGN), spew out vast quantities of radiation and rapidly moving material into space. Most astronomers now accept that AGN, one of the most extreme classes of objects in our Universe, are powered by the release of energy as material falls into the gigantic black hole that resides at the centre of each galaxy.

The plethora of terminology and concepts that have arisen in the field of AGN research means there is a desperate need for a comprehensive and up-to-date text. Active Galactic Nuclei by Julian Krolik fulfils that role. In varying levels of detail, Krolik treats almost every aspect of the AGN phenomenon, starting with the properties of the black hole itself and working outwards to the impact of AGN on their host galaxies. This global survey of AGN physics makes Krolik's book the most useful in the field for years.

Krolik's strength is his emphasis on the well-established physical principles underlying the phenomenology. The more speculative aspects of the field, such as the exotic physics occurring in the immediate vicinity of the black hole, are (justifiably) touched upon only briefly. Thorough descriptions of the fundamental physical processes punctuate the astronomical discussion. In particular, the description of the various mechanisms that generate and influence the observed radiation will be a valuable reference to both students and active AGN researchers. Throughout the book, the reader is given a flavour of the difficulties faced by observers, some of the modern observational breakthroughs and the interplay between the observational and theoretical sides of this vibrant branch of astrophysics.

A few parts of the discussion are confusing. For example, it might be difficult for anyone without a prior knowledge of stellar dynamics to follow the book's treatment of this subject. However, such sections are rare and detract only slightly from the overall strength of the book. One word of warning — the book assumes the reader to be fluent in college-level physics. The brief tutorials in the appendices (on general relativity, magneto-hydrodynamics and other important topics) will serve only to refresh a rusty mind on these topics and may be too brief for the non-specialist.

That said, this is an excellent text and a valuable reference for anybody interested in the physics of these cosmic powerhouses.