News in Science

New evidence backs dark energy

Dark confimation A new study of quasars has provided further evidence that dark energy is accelerating the expansion of the universe.

The study to be published in the Astronomical Journal supports earlier work by scientists including Nobel Laureates Professor Brian Schmidt from the Australian National University, Saul Perlmutter and Adam Riess.

Their discovery was based on the measurement of exploding stars called Type 1a supernovae.

The new work by scientists led by Professor Masamune Oguri from Japan's Kavli Institute for the Physics and Mathematics of the Universe reached their findings by examining gravitationally lensed quasars.

Gravitational lensing uses the mass of a foreground object, such as a galaxy, to act as a lens to bend light coming towards us from a more distant object.

Oguri and colleagues spent ten years examining 100,000 quasars charted by the Sloan Digital Sky Survey. These powerful jets of particles and energy are produced by supermassive black holes in the heart of galaxies from the early universe.

Within this set, the researchers identified 50 gravitationally lensed quasars, allowing them to determine their likely frequency over a given area.

Because accelerated expansion would increase the distance to each quasar and the chances of gravitational lensing, they were able to infer the expansion speed of the universe.

"Our new result using gravitational lensing not only provides additional strong evidence for the accelerated cosmic expansion, but also is useful for accurate measurements of the expansion speed, which is essential for investigating the nature of dark energy," says Oguri.

New approach

Professor Charlie Lineweaver, a cosmologist from the Australian National University, says this study demonstrates a new way to confirm the accelerated expansion of the universe.

"There are five ways to determine how fast the universe's expansion rate is accelerating," says Lineweaver.

"Schmidt used supernovae, which is still the most accurate method. There's also baryonic acoustic oscillations which are density waves that propagate through the universe, there's the cosmic microwave background radiation and you can also count the numbers of star clusters at given distances."

"Having the same conclusions reached by different methods is a tremendously important tool in any scientific research."

"All science is built on that. You can imagine if one method gave you one answer and another method gave you a different answer, so what you're looking for is consistency."