A Crack in Everything

Title: A Crack in Everything – How Black Holes Came in From the Cold and Took Cosmic Centre-stage
Author: Marcus Chown
Publisher: Head of Zeus, 2024 (First)
ISBN: 9781804544327
Pages: 334

The strange thing about the concept of black holes is that even people with hardly any exposure to science writing are well aware of it and its propensity to gobble up anything that ventures near it. Black holes were predicted as a corollary to Einstein’s General Relativity, but they were physically traced only in the 1960s. Sophisticated instruments detected gravitational waves caused by merger of two black holes and new concepts have emerged in the last few decades that revise our understanding of these elusive celestial bodies. Latest research hints that black holes are not exactly ‘black’, but they are some of the most prodigiously luminous objects in the universe. They are not only holes down which matter is sucked in, but sources of immense jets of matter spraying outwards and extending to millions of light years across space. This book envelops the journey of black holes from the periphery of imagination into the very heart of science. Marcus Chown is a science-writer and broadcaster who was a former radio astronomer at California Institute of Technology at Pasadena. He is the author of several books and also launched the Solar System for iPad app, which won ‘The Book Seller’ Digital Innovation of the Year.

The first two chapters make a solid foundation on the theoretical concepts of black holes without appearing too scientific. The first hint of the possibility for existence of this intriguing phenomenon was made by the mathematical solution of Einstein’s General Relativity carried out by Karl Schwarzchild while fighting on the Western front in World War I. He died just five months later but the spark he lit caught on in scientific circles. Beyond a specified size, matter behaved strangely. Subrahmanian Chandrasekhar developed the theory while on a voyage to Europe by sea. Stars up to 1.4 solar masses ended up as white dwarfs when their nuclear fuel was exhausted. If the mass is around 2 to 3 times that of the sun, it may explode as a supernova but the core will turn into a neutron star. Even bigger stars collapse down to a point of infinite gravity. Space will fold in on itself and the star will vanish from view, turning into a black hole. This was hard to grasp for the conservative establishment and the book records the intellectual rivalry between Chandrasekhar and his superior Arthur Eddington which was also tinged with dark shades of racism. However, the threshold size of the star which becomes a black hole is now called the ‘Chandrasekhar Limit’, vindicating the Indian. Chown narrates some amusing effects expected at the ‘event horizon’, the fictitious surface that masks the point of no-return for matter and light falling in. To a distant observer, time at this surface appears to run slower and slower because the space-time is highly distorted. When in fact the matter had gone inside, the observer still sees that the fallen object is hovering on the event horizon. Stephen Hawking once quipped: “In space, no one can hear you scream; and in a black hole, no one can see you disappear”. If you accidentally fell into a black hole, you can be pretty sure that there will be no eye-witnesses.

Even though the discoveries of Schwarzchild and Chandrasekhar occurred much before World War II, the field lay barren and eventless till 1963. In that year, a New Zealand physicist Roy Kerr theoretically found the exact shape of the warped space-time around a spinning black hole by solving Einstein’s equations. The accepted opinion at that time was that when a crushing big star rotates, its centrifugal forces would balance at some point the push of gravity and prevent it from becoming a black hole. Kerr demonstrated that the centrifugal force of a rapidly spinning star could not prevent the formation of a black hole. He also proved that energy is also a form of gravity and the increased kinetic energy would add to gravity and enhance the formation of black hole instead of preventing it. The behaviour of mass and energy are weird when they are very large. The observational proof came just eight years later, in 1971. Paul Murdin and Louise Webster found a blue supergiant in Cygnus galaxy orbiting a black space every 5.6 days that was emitting X-rays. The first black hole was found – on circumstantial evidence. Many were found thereafter and astronomers estimate an astonishing 100 million to exist. Almost every galaxy has a black hole in its centre. Our own Milky Way certainly has a supermassive black hole at its centre. The few dozen black holes so far discovered are no more than the tip of an enormous iceberg.

Early theories of black holes posited them as truly black, set in a black universe and so impossible to identify. This was logical and shaped the minds of many enthusiasts. However, later investigations exposed the fallacy of this postulate. It failed to realise that black holes are likely to be embedded in an environment of interstellar gas and ripped-apart stars. In consuming the material, black holes would superheat it to such high levels as to emit even X-rays, apart from visible light. This idea suggested that, far from being black, black holes could be the most brilliant beacons in the universe. In 1963, quasars were discovered which emitted radiation hugely in excess of its size. These were found to be powered by spinning, supermassive black holes when matter swirls down into such a black hole like water going down a plug hole. This is also a source of energy in the universe. Nuclear fusion which powers the sun has a conversion rate of only one per cent whereas the new source provided up to 40 per cent. In the 1980s, better radio telescopes observed jets of matter stabbing out of the black hole core of galaxies into adjacent radio lobes. It definitively erased the idea that nothing comes out of a black hole. Another concept that changed along with the new influx of data was that supermassive black holes were a rarity that powered only one per cent of galaxies. Observational data from the Hubble Space Telescope proved the existence of many such entities. In fact, one is found to be present in virtually every galaxy, including our own.

Apart from the theoretical and observational aspects of black holes, the author investigates whether these have any significance for the human race. Supermassive black holes have an essential role in the birth and evolution of a galaxy. Through its huge outflow of energy, it transfers the energy into the surrounding galactic environment, gradually clearing the central regions of gas and throttling back star formation. If this did not happen, galaxies would have used up all their gaseous raw material soon after its birth. There would not have been time to produce higher elements which are very much required to sustain higher forms of life, like ours. In this sense, we owe our very existence to the black hole feedbacks that ensured that star formation continued at a sedate rate after the birth of our galaxy and that there was gas left over to give birth to the sun. Chown updates the readers of the recent revolutionary discoveries in relativistic physics such as the experimental detection of gravitational waves from merger of two black holes in 2015. In 2019, intense light was observed from the accretion disk of the merger of two supermassive black holes. Merger of such heavy-gravity stars churn up interesting material too. When two neutron stars merge, gold is generated in copious quantities. The book follows a diligent timeline of the major events related to black holes and the readers observe a conspicuous gap between 1963 and the launch of the Hubble telescope in the 1990s. The reason for this barren period – if it was not coincidental –is not elaborated. One is tempted to assign it to the manned lunar missions of NASA which riveted America’s attention and resources for the race they ran with the Soviets in a bid to reach the moon first. However, the Soviet Union did not make it to the moon.

The book is very agreeably written so as to be interesting to readers having no advanced training in science. Chown has taken care not to include any equations or unnecessary numbers. Hawking had one remarked that had he omitted the lone equation E = mc^2 in his epic book, ‘A Brief History of Time’, it would have doubled its sales. A lot of scientific facts are seamlessly interspersed with interesting biographical accounts of the inventers along with amusing asides. It appears that the nomenclature of ‘potential energy’ which we had studied in school has now changed to ‘gravitational energy’; just as kinetic energy is now referred to as ‘energy of motion’ in this book. A good popular book on physics was the need of the times as the old crop ended in the first decade of this century. This book neatly fits the bill. Latest findings and information till 2023 are updated in the book. However, the last third of the book seems to be full of somewhat uninteresting speculation and unnecessary elaboration of not very important ideas, some of which may never be discovered or disproved. They may remain just intelligent speculation for a long period to come. In spite of this minor hiccup, this book is a must-read for enthusiasts of physics, astronomy and cosmology.

The book is highly recommended.

Rating: 4 Star