Nonthermal particles and photons in starburst regions and superbubbles

Abstract

Starforming factories in galaxies produce compact clusters and loose associations of young massive stars. Fast radiation-driven winds and supernovae input their huge kinetic power into the interstellar medium in the form of highly supersonic and superalfvenic outflows. Apart from gas heating, collisionless relaxation of fast plasma outflows results in fluctuating magnetic fields and energetic particles. The energetic particles comprise a long-lived component which may contain a sizeable fraction of the kinetic energy released by the winds and supernova ejecta and thus modify the magnetohydrodynamic flows in the systems. We present a concise review of observational data and models of nonthermal emission from starburst galaxies, superbubbles, and compact clusters of massive stars. Efficient mechanisms of particle acceleration and amplification of fluctuating magnetic fields with a wide dynamical range in starburst regions are discussed. Sources of cosmic rays, neutrinos and multi-wavelength nonthermal emission associated with starburst regions including potential galactic "PeVatrons" are reviewed in the global galactic ecology context.

The origin of Galactic cosmic rays: Challenges to the standard paradigm

“…It is possibly for this reason that several alternative ideas to the SNR paradigm, proposed years ago to explain the origin of CRs, have been recently revived. The list includes the acceleration of particles at the Galactic centre (see 12 for an early reference, 255 for a recent one), at stellar winds (see 280 for an early reference, 281 for a recent one), in superbubbles (see 282,283 for early references, [259][260][261] for recent ones), or the explanation of at least part of the CR spectrum with a single (or very few) sources (see 284 for an early reference, 285 for a recent one). Finally, other classes of sources (such as X-ray binaries 286,287 or pulsar wind nebulae 288 ) have been considered, and attempts to develop truly heterodox scenarios were published, as we briefly discussed in Section 3.1.5.…”

“…According to the most popular alternative view, superbubbles rather than isolated SNRs may explain the entire spectrum of Galactic CRs up to the ankle. 256,[259][260][261] This scenario, however, surprisingly received much less attention than the SNR paradigm, and thus needs to be further investigated. In a (definitely non-orthodox) paper in 1972 Brecher and Burbidge 262 proposed that all (hadronic) CR b are extragalactic (EG) and fill the universe at the same level as in the Galaxy.…”