Don't Get Sucked In

by Andrew Crumey

Review of Black Hole by Marcia Bartusiak. Literary Review, July 2015.

In 1756 troops of the Nawab of Bengal over-ran a fort manned by British forces. The captured occupants were imprisoned in a cell where most died overnight from heat exhaustion. The precise numbers are unknown, but the Black Hole of Calcutta was a colonial horror story imprinted on the minds of schoolchildren over the next two centuries of British imperialism. The tale was well known to American astrophysicist Robert Dicke, and according to Marcia Bartusiak's engagingly written scientific history, it was Dicke who transferred the epithet to those escape-proof cosmic dungeons that are the subject of her book.

Science writers, unlike biographers or political historians, aren't generally expected to come up with some new opinion or revelation in order to justify adding another volume to the bookshelf. Discovery, after all, is what the scientists are meant to have done, and Bartusiak's work is for the most part a faithful and accurate chronicle of a well-trodden subject. We are led through Einstein's general relativity, its unexpected prediction of gravitationally collapsed objects, their possible discovery by means of their influence on surrounding matter, and Stephen Hawking's realisation that black holes "ain't so black", emitting radiation of their own. All of this is well told, in non-technical terms that stretch imagination rather than comprehension. For me, though, it's Dicke's place in the story that comes as an interesting surprise. Read just about any other book on the subject, and credit for the name is more likely to be attributed to Dicke's contemporary, John Archibald Wheeler.

Dicke died in 1997, Wheeler in 2008, and the latter claimed only to have popularised the name "black hole", which first appeared in print in 1964. But Bartusiak cites physicist Hong-Yee Chiu who attended a talk Robert Dicke gave around 1960, where he said the hypothetical objects were "like the Black Hole of Calcutta". According to Bartusiak, "It was one of Dicke's favourite expressions... His sons recall their father exclaiming, 'Black Hole of Calcutta!' whenever a household item appeared to have been swallowed up and gone missing."

Whether this is more interesting than getting to grips with spherically symmetric solutions of general relativity is a matter of personal taste. Die-hard physicists can be apt to see the history of their subject as trivial gossip about the contingencies of human life, which is exactly why we need people with a different outlook to chronicle what they do. But it is science that occupies most of this fairly brief book, and Bartusiak relates it with aplomb.

The astronomical story in fact begins, like the name, in the eighteenth century. Isaac Newton and his followers believed light to be made of tiny solid particles. Throw a ball in the air and Earth's gravity will bring it back down; shoot it upwards at a speed greater than eleven kilometres per second (Earth's "escape velocity") and it won't come back, instead flying off into space. What if a planet or star were so massive that its escape velocity was greater than the speed of light? John Michell asked this in 1783, and suggested that astronomers search for light-trapping "dark stars" which might betray themselves through their tug on neighbouring objects. He was a black-hole theorist ahead of his time.

Newton's particle theory of light was wrong, and so was his theory of gravity. Einstein's general relativity offered a more accurate one, describing gravitation as a distortion of space-time. As a consequence, light would be bent by strong fields. Michell had the right idea for the wrong reason.

Einstein's theory was a recipe rather than a meal: his equations had to be solved in order to make predictions, and finding solutions was hard. Karl Schwarzschild found one in 1916. It showed that if an object's mass could be contained within a certain volume, then light - or anything else - would be unable to escape the interior. The boundary of this critical volume is known as the event horizon, and its size is the Schwarzschild radius, a curiously appropriate name since Schwarzschild roughly means "black shield".

Bartusiak recounts the decades of controversy that followed. The equations suggested that a very large star could collapse under its own weight, shrinking right down to a point or "singularity", hidden within its own event horizon. It was not until the 1960s that the existence of such objects began to seem plausible, and in 1971 the first candidate emerged, named Cygnus X-1 after its location in the night sky, in the neck of the celestial swan. It is now believed to be a collapsed star roughly fifteen times more massive than the Sun, compressed within a radius of about forty four kilometres. It is closely orbiting a visible star, some of whose material gets pulled round the black hole, creating the intense X-rays that reveal its presence.

Since then, numerous black holes have been discovered, including a "supermassive" one at the centre of our galaxy. Exactly how it formed is still debated, whether from a coalescing of stars or a merger of smaller black holes. What is no longer doubted is the existence of these bizarre objects.

Bartusiak explains the unpleasant result of falling into one, being stretched like spaghetti while to observers on Earth you would seem frozen forever at the point of no return. She deals with some popular questions such as why black holes don't just eat up everything. The answer is that you could orbit one forever without noticing ill effects, it's only if you stray too close that things go awry. She ends with the hunt for gravitational waves, produced when black holes form. She reports on what seemed like the most exciting astronomical news of 2014, the claim by the BICEP2 team that gravitational waves from the Big Bang had been detected. That has now been discounted; but since my copy was an advance proof, maybe that false alarm will be quietly removed from what is otherwise a reliable and readable account of an amazing story.