This is a charming and accessible introduction to black holes by YouTube's popular astrophysicist, Dr Becky. To help understand the characteristics of black holes and the science behind them, Dr Becky provides background summaries of a range of associated astrophysics topics including the nature of light, atomic structure, gravity, and the classification and life cycles of stars. The text is a mix of science and history with the reader being introduced to the development of all the relevant scientific concepts and key players whom Dr Becky calls "BNiP's" (Big Names in Physics).

Dr Becky notes that astrophysics is a young science, where mankind has only appreciated the true scale of the universe for the past 100 years. Black holes were only accepted theoretically in the 1960s (thanks to Hawking, Penrose & Kerr) and the black hole in the centre of the Milky Way was only confirmed by observation in 2002: "...humans managed to put someone on the Moon before we could comprehend that all our lives have been spent inexorably orbiting around a black hole".

The full title of the book is "A Brief History of Black Holes and why nearly everything you know about them is wrong", so what misconceptions can we possibly have about them? Firstly, the term "black hole" is a bit of a misnomer. It is easy to think of a black hole as a "hole" as they are usually illustrated in 2D (to help people better understand the concepts behind general relativity) with the warped space-time resembling a whirlpool or drain that everything passing beyond the event horizon falls towards. Dr Becky corrects this view in Chapter 3: "...a black hole is the furthest thing from a hole you can get. A black hole isn't the absence of something, it's the presence of everything; matter in its densest possible form. I like to think of them more like mountains of matter than holes in the ground."

Black holes may be considered "black" because nothing, not even light, can escape from beyond the event horizon, however, the accretion disks of hot material encircling many large black holes (and located further out than the event horizon) are very strong emitters of energetic X-rays and other forms of energy. Dr Becky tells us that, "Because of accretion, black holes are not black at all; they end up being the brightest objects in the Universe." As a result, she offers a revised descriptive metaphor for black holes, calling them "... blindingly bright mountains"(!)

In this book, Dr Becky discusses black holes from small to "supermassive" and even gets excited about the concept of one in the further reaches of our solar system which may seem a worrying concept to the layman. She takes this opportunity to tell the story of the hunt for "Planet X" which was sparked by something apparently causing anomalies to the orbits of Neptune & Uranus. This eventually led to Clyde Tombaugh's discovery of Pluto back in 1930 which was immediately hailed as a new planet. However, Pluto (and its moon, Charon) are much too small to create the "wobbles" in the orbital path of the ice giants which have subsequently been found to coincide with the Sun's 11-year activity cycle.

Where does the black hole come in? Well, there may still be something beyond the orbit of Neptune that is shepherding "dwarf planet wannabe" Sedna on its highly elliptical 11,000-year orbit around the Sun. Sedna could be interacting with a large "Planet X" or Dr Becky suggests a small primordial black hole. At about five times the mass of the Earth, she explains that such a black hole would have to be very small with an event horizon only "about the size of a tennis ball"! Devoid of an accretion disk, such a black hole would continue to elude astronomers and remain hidden.

All in all this book is a pleasant read and flows well despite its fixation with frequent, often overly-long footnotes that insist on pulling the reader away from the main body of text. The information is informed, up-to-date and delivered with humour, analogies and popular culture references. Rather akin to a chat with a friendly astrophysicist over a drink at your favourite coffee house.