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New data, old rivalries, and enduring questions fill a welcome overview of black hole research

Einstein’s Monsters: The Life and Times of Black Holes

Chris Impey
Norton
2018
315 pp.
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What happens at the black hole event horizon, where time stands still and intuition breaks down? In the opening chapter of his new book, Einstein’s Monsters, astronomer and popular science writer Chris Impey puts the problem succinctly: “It made no sense for a physical object to have zero size and infinite mass density. Einstein’s theory had created something monstrous.”

Impey does an admirable job describing multiple facets of the often contradictory field of black hole astrophysics, including its history, science, and colorful human interactions. For example, we now know that most astrophysical black holes are notoriously difficult to detect and observe, and yet some are the brightest x-ray sources in the sky and can be seen from across the entire universe. They seem to come in two sizes: small and extra-extra-extra-large. The small ones have huge densities, whereas the largest ones are lighter than air.

Even the (seemingly) most fundamental fact about black holes—that not even light can escape one—is not entirely true. In the 1970s, Stephen Hawking proved that black holes of all sizes give off a faint glow of extremely low-temperature blackbody radiation.

In the far distant future, every black hole in the universe will eventually evaporate, leaving nothing behind but a dilute, near-uniform bath of radio waves. A related paradox: An astronaut plunging into a black hole would feel nothing as she slips quietly past the event horizon and reaches the singularity only a few moments later, yet to her crew mates watching from the safety of the nearby mothership, it would take an eternity for her to even reach the horizon. Like Zeno’s tortoise, she would seem to get closer and closer, fainter and fainter, but never quite disappear.

In addition to these physical contradictions, the book also covers many of the field’s more interesting human conflicts and competitions throughout the past century: Eddington versus Chandrasekhar, Zwicky versus Sandage, Thorne versus Hawking, even Einstein versus Einstein. Impey paints a colorful picture of the personalities involved, including personal anecdotes from his own firsthand interactions with many of the leading actors of the story.

One may reasonably ask, “Does the world really need another popular science book about black holes?” Anyone who has read and enjoyed Kip Thorne’s gold standard Black Holes and Time Warps will learn relatively little from Einstein’s Monsters. Yet the intended target audience is more likely to have read Hawking’s A Brief History of Time (if they have read anything on the topic) and thus may not be familiar with many of the critical observational discoveries over the past half-century.

For the next generation of popular astronomy buffs, Einstein’s Monsters is a reasonable entry point, covering a broad—if not particularly deep—range of theoretical and observational topics in black hole research. Particularly welcome, even for more experienced black hole aficionados, are the excellent chapters about the Laser Interferometer Gravitational-Wave Observatory’s recent discovery of gravitational waves and the Event Horizon Telescope’s imminent discovery of black hole shadows.

Impey’s broad and relatively cursory approach to black holes mirrors his earlier works in popular astronomy, this being his seventh book in about as many years. Unfortunately, this prolific productivity is occasionally betrayed by factual errors in the text, especially in the more theoretical passages. In chapter 8, for example, Impey claims that fermions and bosons cannot interact with each other, when in fact that is exactly how photons and gluons convey the fundamental forces of nature. Elsewhere, he asserts that Mercury’s precession is 5600 arc sec per century, which is off by an order of magnitude. A number of theoretical results—for example, using x-ray oscillations to measure black hole mass and spin—are also quoted as established fact despite widespread skepticism in the research community.

Certain passages, and even chapters, of Einstein’s Monsters have a distinctly haphazard feel to them, throwing together a collection of topics without an obvious theme. Chapter five jumps from g-ray bursts to intermediate-mass black holes to microquasars to numerical relativity and then cosmological N-body simulations. Perhaps the goal here is to impress the reader with how important black holes are in modern astronomy, but it gives the impression of disorganization.

Despite these few shortcomings, Einstein’s Monsters will be sure to capture the imagination of most who pick it up, simultaneously convincing the reader that these monsters, while in fact quite certainly real, should be loved and not feared.

About the author

The reviewer is at the Sciences and Exploration Directorate, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.