This book highlights the biggest gaps in our understanding of the universe. The text aims to clarify what exactly it is that we do not understand in our current picture of the universe and the objects it contains. After briefly describing how astronomers see and gather information from our universe, the book describes topics where our knowledge is incomplete - dark matter, dark energy, the Hubble constant/tension, deaths of massive stars, mysteries associated with black holes, neutron stars, binary/multiple systems, and more.

Each chapter gives a summary of the state of knowledge in a particular astrophysics research area and then proceed to explain where the mysteries lie - where we have new territory to explore and much to learn. To appeal to students and researchers, there is also a separate section in each chapter containing some simple maths/calculations plus references to more technical books and sources. This book fills an important need in the current scientific literature. It not only serves the scientifically interested public, but also burgeoning astronomy students, by clarifying where we lack a solid understanding of our universe. The book helps elucidate research areas to pursue for young students with astronomy career aspirations. It also helps the general audience gain a better appreciation for where to critically examine scientific results reported in the media. This book is intended for both general audiences, students, and researchers in other fields.