The concordance cosmology model is poorly tested at high redshifts. Here the expansion rate of the Universe in the range 0.5 < z < 5.1 is measured based on a Hubble diagram of quasars, whose distances are estimated from their X-ray and ultraviolet emission.

Simulations of early galaxy formation suggest that the dynamics of structure formation, rather than the Lyman–Werner flux, drives the formation of massive black holes in the early Universe.

The second decade of fast radio burst (FRB) astronomy has started at pace, with detections of tens of new FRBs from newly operational facilities such as ASKAP and CHIME. Evan Keane looks forward to the upcoming years and the discoveries they will bring.

Gravitational-wave observations of binary neutron-star mergers will enable precision measurements of the Hubble constant within five years.

The primordial abundance of helium, set minutes after the Big Bang, is typically measured in star-forming regions in local metal-poor galaxies. Here the helium abundance of an intergalactic gas cloud is calculated using the light of a background quasar instead.