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Ultracompact stellar clusters in the Galactic Centre are likely to be major contributors to the Galactic cosmic ray flux in the multi-TeV energy range. Observations of the diffuse gamma-ray emission from the Galactic Centre and two young massive star clusters correlate with the cosmic-ray distribution.

Observations of γ-rays from the Crab pulsar suggest that the energy of the pulsar wind changes from electromagnetic to kinetic over a relatively short distance close to the light cylinder of the pulsar.

A magnetic galactic halo featuring coherent ridges several kiloparsecs above and below the Galactic Disk has been detected in multi-wavelength observations. The halo is probably a consequence of outflows driven by active star-forming regions in the disk.

A discovery of the brightening and decay of X-ray hot spots in the shell of the SNR RX J1713.˜73946 on a one-year timescale is reported. This rapid variability shows that the X-rays are produced by ultrarelativistic electrons through a synchrotron process.

The cosmic rays that permeate our Galaxy have been attributed to various sources. The discovery of high-energy γ-rays from a supernova remnant at last provides concrete evidence for one of the proposed theories.

High-energy radiation originating in the wind termination shock of young star clusters has been observed, without contamination from other sources such as supernovae. This adds the winds of star clusters to the list of cosmic-ray accelerators within the Galaxy.

Observations of γ-rays with energies up to 1.4 PeV find that 12 sources in the Galaxy are PeVatrons, one of which is the Crab Nebula.

Through mapping the gamma-ray flux in giant molecular clouds, it appears that low-energy cosmic rays hardly penetrate into dense, potentially star-forming, clumps. This finding implies a slower diffusion of cosmic rays in these clumps, possibly caused by higher levels of magnetic turbulence than anticipated.

The origin of Galactic positrons that produce gamma ray emission when annihilated is still debated. Mergers of two white dwarfs are likely to be the main source of these positrons. Such mergers produce sub-luminous, thermonuclear supernovae.

A bright patch in the Fermi bubbles, previously attributed to a jet launched by the Galaxy’s central black hole, is actually due to gamma-ray emission by millisecond pulsars in a background, satellite galaxy of the Milky Way.

Our understanding of the relatively newly recognized phenomenon of haloes of gamma-ray emission around Galactic pulsars is summarized, from observational and theoretical perspectives, together with their implication for the acceleration of cosmic rays.

Cosmic rays at petaelectronvolt energies permeate the Milky Way, but their origin is unknown. This Review Article summarizes the physics required to accelerate particles to these ultrahigh energies, and their potential astrophysical sources (‘PeVatrons’).

X-ray observations of the core of the Perseus cluster reveal a remarkably quiescent atmosphere in which the gas has a line-of-sight velocity dispersion of about 164 kilometres per second in the region 30–60 kiloparsecs from the central nucleus; turbulent pressure support in the gas is four per cent of the thermodynamic pressure, necessitating only a small correction to the total cluster mass determined from hydrostatic equilibrium.

High-resolution X-ray spectra show near-solar abundances of chromium, manganese and nickel with respect to iron in the Perseus cluster, suggesting that the progenitors of type Ia supernovae could be near- and sub-Chandrasekhar-mass white dwarfs.