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Added by
Christopher S. Reynolds
Publication date
2019
fields
Physics
and research's language is
English
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With each passing decade, we gain new appreciation for the dynamic, connected, and often violent nature of the Universe. This reality necessarily places the study of high-energy processes at the very heart of modern astrophysics. This White Paper illustrates the central role of high-energy astrophysics to some of the most pressing astrophysical problems of our time, the formation/evolution of galaxies, the origin of the heavy elements, star and planet formation, the emergence of life on exoplanets, and the search for new physics. We also highlight the new connections that are growing between astrophysicists and plasma physicists. We end with a discussion of the challenges that must be addressed to realize the potential of these connections, including the need for integrated planning across physics and astronomy programs in multiple agencies, and the need to foster the creativity and career aspirations of individual scientists in this era of large projects.
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Neutrinos are unique cosmic messengers. Present attempts are directed to extend the window of cosmic neutrino observation from low energies (Sun, supernovae) to much higher energies. The aim is to study the most violent processes in the Universe which accelerate charged particles to highest energies, far beyond the reach of laboratory experiments on Earth. These processes must be accompanied by the emission of neutrinos. Neutrinos are electrically neutral and interact only weakly with ordinary matter; they thus propagate through the Universe without absorption or deflection, pointing back to their origin. Their feeble interaction, however, makes them extremely difficult to detect. The years 2008-2010 have witnessed remarkable steps in developing high energy neutrino telescopes. In 2010, the cubic-kilometre neutrino telescope IceCube at the South Pole has been completed. In the Mediterranean Sea the first-generation neutrino telescope ANTARES takes data since 2008, and efforts are directed towards KM3NeT, a telescope on the scale of several cubic kilometres. The next years will be key years for opening the neutrino window to the high energy Universe. With an instrumented volume of a cubic kilometre, IceCube is entering a region with realistic discovery potential. Discoveries or non-discoveries of IceCube will have a strong impact on the future of the field and possibly mark a moment of truth. In this review, we discuss the scientific case for neutrino telescopes, describe the detection principle and its implementation in first- and second-generation installations and finally collect the existing physics results and the expectations for future detectors. We conclude with an outlook to alternative detection methods, in particular for neutrinos of extremely high energies.
Modern astrophysics, especially at GeV energy scales and above is a typical example where several disciplines meet: The location and distribution of the sources is the domain of astronomy. At distances corresponding to significant redshift cosmological aspects such as the expansion history come into play. Finally, the emission mechanisms and subsequent propagation of produced high energy particles is at least partly the domain of particle physics, in particular if new phenomena beyond the Standard Model are probed that require base lines and/or energies unattained in the laboratory. In this contribution we focus on three examples: Highest energy cosmic rays, tests of the Lorentz symmetry and the search for new light photon-like states in the spectra of active galaxies.
We discuss some of the tests of Lorentz symmetry made possible by astrophysical observations of ultrahigh energy cosmic rays, gamma-rays, and neutrinos. These are among the most sensitive tests of Lorentz symmetry violation because they are the highest energy phenomena known to man.
High-energy astrophysics observations provide the best possibilities to detect a very small violation of Lorentz invariance, such as may be related to the structure of space-time near the Planck scale. I discuss the possible signatures of Lorentz invariance violation that can be manifested by observing the spectra, polarization, and timing of gamma-rays from active galactic nuclei and gamma-ray bursts. Other sensitive tests are provided by observations of the spectra of ultrahigh-energy cosmic rays and very high-energy neutrinos. I also discuss a new time-of-flight analysis of observations of GRB 090510 by the Fermi gamma-ray Space Telescope. These results, based on high-energy astrophysical observations, have fundamental implications for space-time physics and quantum gravity models.
Electromagnetic observations of the sky have been the basis for our study of the Universe for millennia, cosmic ray studies are now entering their second century, the first neutrinos from an astrophysical source were identified three decades ago, and gravitational waves were directly detected only four years ago. Detections of these messengers are now common. Astrophysics will undergo a revolution in the 2020s as multimessenger detections become routine. The 8th Astro2020 Thematic Area is Multimessenger Astronomy and Astrophysics, which includes the identification of the sources of gravitational waves, astrophysical and cosmogenic neutrinos, cosmic rays, and gamma-rays, and the coordinated multimessenger and multiwavelength follow-ups. Identifying and characterizing multimessenger sources enables science throughout and beyond astrophysics. Success in the multimessenger era requires: (i) sensitive coverage of the non-electromagnetic messengers, (ii) full coverage of the electromagnetic spectrum, with either fast-response observations or broad and deep high-cadence surveys, and (iii) improved collaboration, communication, and notification platforms.
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