Prior to the 1920s it was generally thought, with a few exceptions, that our galaxy, the Milky Way, was the entire Universe. Based on the work of Henrietta Leavitt with Cepheid variables, astronomer Edwin Hubble was able to determine that the Andromeda Galaxy and others had to lie outside our own. Moreover, based on the work of Vesto Slipher, involving the redshifts of these galaxies, Hubble was able to determine that the Universe was not static, as had been previously thought, but expanding. The number of galaxies has also been expanding, with estimates varying from 100 billion to 2 trillion. While every galaxy in the Universe is interesting just by its very fact of being, the author has selected 60 of those that possess some unusual qualities that make them of some particular interest. These galaxies have complex evolutionary histories, with some having supermassive black holes at their core, others are powerful radio sources, a very few are relatively nearby and even visible to the naked eye, whereas the light from one recent discovery has been travelling for the past 13.4 billion years to show us its infancy, and from a time when the Universe was in its infancy. And in spite of the vastness of the Universe, some galaxies are colliding with others, embraced in a graceful gravitational dance. Indeed, as the Andromeda Galaxy is heading towards us, a similar fate awaits our Milky Way. When looking at a modern image of a galaxy, one is in awe at the shear wondrous nature of such a magnificent creation, with its boundless secrets that it is keeping from us, its endless possibilities for harboring alien civilizations, and we remain left with the ultimate knowledge that we are connected to its glory.

The meaning of "quark matter" is twofold: 1) It refers to compound states known as "subquarks" (the most fundamental constituents of matter), with quarks consisting of nuclear matter or "nucleons" (the constituents of the nucleus), and 2) compound states of quarks that consist of roughly equal numbers of up, down, and strange quarks, and which may be absolutely stable. Recently, both types of quark matter have become very intriguing subjects in physics and astronomy since the recently discovered Higgs boson, which may be taken as a composite object (possibly, a bound state of subquark-antisubquark pairs). Additionally, many recently observed compact stars have been considered "strange stars" (stars consisting of quark matter). In this book, these subjects in physics and astronomy are discussed without requiring readers to comprehend mathematical details. This book consists of three chapters: Chapter One: "Quark Matter and Strange Stars", Chapter Two: "Composites of Subquarks as Quark Matter", and Chapter Three: "Dark Energy, Dark Matter, and Strange Stars". Their contents include the following: In Chapter One, quark matter and strange stars are discussed in detail. In Chapter Two, the unified subquark model of all fundamental particles (quarks, leptons, and gauge and Higgs bosons) and forces (strong, electromagnetic, weak, and gravitational forces) is discussed in detail. In Chapter Three, pregeometry, in which the general theory of relativity for gravity can be derived as an approximate theory at long distances, is briefly reviewed. Furthermore, special and general theories of "inconstancy" in pregeometry in which fundamental physical constants may vary are introduced. Finally, possible solutions to the most puzzling problem in current cosmology of dark energy and dark matter in the universe are presented. Between Chapters One and Two, pictures of Dr. Abdus Salam added, as Dr. Salam was one of the founders of subquark models. Also, between Chapters Two and Three, pictures of Dr. Andrei Sakharov are added, as Dr. Sakharov was the founder of pregeometry.

Recent cosmological observations have posed a challenge for traditional theories of gravity: what is the force driving the accelerated expansion of the universe? What if dark energy or dark matter do not exist and what we observe is a modification of the gravitational interaction that dominates the universe at large scales? Various extensions to Einstein's General Theory of Relativity have been proposed, and this book presents a detailed theoretical and phenomenological analysis of several leading, modified theories of gravity. Theories with generalised curvature-matter couplings are first explored, followed by hybrid metric-Palatini gravity. This timely book first discusses key motivations behind the development of these modified gravitational theories, before presenting a detailed overview of their subsequent development, mathematical structure, and cosmological and astrophysical implications. Covering recent developments and with an emphasis on astrophysical and cosmological applications, this is the perfect text for graduate students and researchers.