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The Hubble constant can be estimated from measurements of both the early and late Universe, but the two estimates disagree. In 2019 a number of independent measurements using different methods made this discrepancy harder to ignore.
In 2019, new optical phenomena have been revealed in stacks of atomically thin semiconducting transition metal dichalcogenides. These effects can be understood in terms of well-known, but also new, exotic, types of exciton.
Black holes — from which no light escapes — have now been ‘seen’ by electromagnetic and gravitational-wave observatories. Datasets from these observations, released in the past year, give important hints about the environment, origin and growth of black holes.
