Neutron stars, whether isolated or in a binary system, display a varied and complex phenomenology, often accompanied by extreme variability of many time scales, which takes the form of pulsations due to the object rotation, quasi-periodicities associated to accretion of matter, and explosions due to matter accreted on the surface or to starquakes of highly magnetized objects. This book gives an overview of the current observational and theoretical standpoint in the research on the physics under the extreme conditions that neutron stars naturally provide. The six chapters explore three physical regions of a neutron star: the space around it, where accretion and pulsar companions allow testing of general relativity its surface, where millisecond pulsation and X-ray burts provide clues about general relativistic effects and the equation of state of neutron matter its interior, of course, inaccessible to direct observations, can nevertheless, be probed with all observational parameters related to neutron star variability.

This book summarizes the recent progress in the physics and astrophysics of neutron stars and, most importantly, it identifies and develops effective strategies to explore, both theoretically and observationally, the many remaining open questions in the field. Because of its significance in the solution of many fundamental questions in nuclear physics, astrophysics and gravitational physics, the study of neutron stars has seen enormous progress over the last years and has been very successful in improving our understanding in these fascinating compact objects. The book addresses a wide spectrum of readers, from students to senior researchers. Thirteen chapters written by internationally renowned experts offer a thorough overview of the various facets of this interdisciplinary science, from neutron star formation in supernovae, pulsars, equations of state super dense matter, gravitational wave emission, to alternative theories of gravity. The book was initiated by the European Cooperation in Science and Technology (COST) Action MP1304 “Exploring fundamental physics with compact stars” (NewCompStar).

This book is an introduction to gravitational waves and related astrophysics. It provides a bridge across the range of astronomy, physics and cosmology that comes into play when trying to understand the gravitational-wave sky. Starting with Einstein's theory of gravity, chapters develop the key ideas step by step, leading up to the technology that finally caught these faint whispers from the distant universe. The second part of the book makes a direct connection with current research, introducing the relevant language and making the involved concepts less mysterious. The book is intended to work as a platform, low enough that anyone with an elementary understanding of gravitational waves can scramble onto it, but at the same time high enough to connect readers with active research - and the many exciting discoveries that are happening right now. The first part of the book introduces the key ideas, following a general overview chapter and including a brief reminder of Einstein's theory. This part can be taught as a self-contained one semester course. The second part of the book is written to work as a collection of "set pieces" with core material that can be adapted to specific lectures and additional material that provide context and depth. A range of readers may find this book useful, including graduate students, astronomers looking for basic understanding of the gravitational-wave window to the universe, researchers analysing data from gravitational-wave detectors, and nuclear and particle physicists.

When a massive enough star dies, it can undergo a supernova explosion, releasing enormous amounts of energy and leaving behind a turbulent dead star core. The matter and gas of the star compresses down, and due to conservation of angular momentum, the dead star core begins to rotate many times faster and demonstrates many extreme properties. These dead star cores, called neutron stars, possess densities trillions of times those of the Sun, rotate hundreds of times per second, and have magnetic fields trillions of times those of Earth. The explosion and core-collapse event that results in these objects have been studied and analysis of these events allow researchers to better understand the fringes of physics. Despite vigorous simulations and studies by many astronomical researchers for 50 years, much still eludes us on supernovae explosion and neutron star phenomenon. Because of their distance and other observational challenges, very little is still known about the processes inside of neutron stars and the supernovae core collapses that generate them. One of the promising aspects for future investigation involves determining properties based off of their emitted gravitational waves and neutrinos, one of the few potential ways we can gather insight into their internal mechanisms. The LIGO observatory has detected gravitational waves from merging neutron stars, providing useful data to discover more of the state of matter inside neutron stars. For my project, I investigate the gravitational wave signals from singular neutron star sources. During the proto-neutron star phase (PNS), where the star core is still thermodynamically unstable and highly energetic right after supernova collapse, gravitational waves have been predicted to be generated. These waves can be generated from internal means, such as convection, or external means, such as the accretion of matter. Modeling these events will provide deeper comprehension into what modes of oscillation are dominant and capable of emitting gravitational waves. This, in turn, will guide the interpretation of future observations.

This book includes nine chapters written by internationally recognized experts, covering all aspects of millisecond pulsars in one concise and cohesive volume. These aspects include pulsations powered by stellar spin, accretion and thermonuclear burning of accreted matter, their physics and utility, stellar evolution and the extreme physics of super-dense stellar cores. The book includes substantial background material as well as recent theoretical and multi-wavelength observational results. The volume will thus be useful for professional astronomers and graduate students alike. What is the behavior of the strong nuclear interaction, and what are the matter constituents at ultrahigh densities in neutron star cores? How do old neutron stars in binaries evolve? How does their magnetosphere interact with the surrounding plasma to accelerate particles and emit radiation observed at all wavelengths? These are just a few of the questions that millisecond pulsars are helping us answer and will settle in the near future with the next generation of instruments. Such quickly rotating, highly magnetized neutron stars are remarkable natural laboratories that allow us to investigate the fundamental constituents of matter and their interactions under extreme conditions that cannot be reproduced in terrestrial laboratories.

This volume extends the ISSI series on magnetic fields in the Universe into the domain of what are by far the strongest fields in the Universe, and stronger than any field that could be produced on Earth. The chapters describe the magnetic fields in non-degenerate strongly magnetized stars, in degenerate stars (such as white dwarfs and neutron stars), exotic members called magnetars, and in their environments, as well as magnetic fields in the environments of black holes. These strong fields have a profound effect on the behavior of matter, visible in particular in highly variable processes like radiation in all known wavelengths, including Gamma-Ray bursts. The generation and structure of such strong magnetic fields and effects on the environment are also described.

This book deals with the interdisciplinary areas of nuclear physics, supernovae and neutron star physics. It addresses the physics and astrophysics of the spectacular supernova explosions, starting with the collapse of massive stars and ending with the birth of neutron stars or black holes. Recent progress in the understanding of core collapse supernova (CCSN) and observational aspects of future detections of neutrinos from CCSN explosions are discussed. The other main focus in this text is the novel phases of dense nuclear matter, its compositions and equation of state (EoS) from low to very high baryon density relevant to supernovae and neutron stars. The multi-messenger astrophysics of binary neutron star merger GW170817 and its relation to EoS through tidal deformability are also presented in detail. The synthesis of elements heavier than iron in the supernova and neutron star environment by the rapid (r)-process are treated here with special emphasis on the nucleosynthesis in the ejected material from GW170817. This monograph is written for graduate students and researchers in the field of nuclear astrophysics.