Observations of radio emission from distant quasars have given new weight to the theory of dark energy – a kind of vacuum energy density that changes the acceleration of the universe.
Quasars are incredibly bright – they emit more light than 100 galaxies from a volume no larger than our solar system. In the recent study, radio astronomers searched for quasars that had been gravitationally lensed (Einstein’s theory of general relativity shows that the gravitational pull from massive objects is able to deflect rays of light as a lens does).
The astronomers compared the number of gravitationally lensed quasars with the number predicted from observations of intervening galaxies capable of lensing. From this they deduced that around two-thirds of the universe’s energy appears to be in the form of dark energy – without the influence of dark energy, only about half the number of lensing events actually observed would be seen.
This is independent evidence in support of dark energy, and confirms previous analysis based on observations of supernovae and of the cosmic microwave background (CERN Courier June 2001). The study was carried out using the MERLIN radio interferometer based at Jodrell Bank, UK, the Very Large Array and the Very Long Baseline Array, US.
