Multimessenger astronomy

1. Introduction -- 2. Background -- 2.1. What powers cosmic emission? -- 2.2. Cosmic messengers -- 3. Current directions -- 3.1. Gravitational wave observations--LIGO -- 3.2. High-energy neutrino observations--IceCube -- 3.3. Connecting the messengers : combined observations and interpretation -- 4. Outlook -- 5. Conclusion.;With the recent discovery of gravitational waves and high-energy cosmic neutrinos, we are witnessing the beginning of a new era in multimessenger astronomy. The exploration of the Universe through these new messengers, along with electromagnetic radiation and cosmic rays, gives us new insights into the most extreme energetic cosmic events, environments and particle accelerators. The objects of interest range from galaxies with accreting supermassive black holes in their centre to collapsing stars and coalescing stellar black holes. In this ebook we provide an introduction to the scientific questions surrounding these new messengers and the detectors and observational techniques used to study them, together with an overview of current and future directions in the field.