A Supernova Sheds Light on Dark Energy

A discovery by astronomers using the Hubble Space Telescope supports the notion that the Universe is filled with a mysterious form of energy pushing galaxies apart at an ever-increasing rate.

NASA's Hubble Space Telescope has spotted a burst of light from an exploding star located much farther from Earth than any previously seen - a supernova blast in the early Universe that is casting light on a mystery of truly cosmic scale.

This stellar explosion is extraordinary not only because of its tremendous distance - 10 billion light-years from our planet - but also because it greatly bolsters the case for the existence of a mysterious form of "dark energy" pervading the cosmos. The concept of dark energy, which shoves galaxies away from each other at an ever-increasing speed, was first proposed, then discarded, by Albert Einstein early in the last century.

The Hubble discovery also reinforces the startling idea that the universe only recently began speeding up -- it offers the first tantalising observational evidence that gravity began slowing down the expansion of the universe after the Big Bang, and only later did the repulsive force of dark energy win out over gravity's grip.

The team of astronomers, led by Adam Riess of the Space Telescope Science Institute (STScI), made the discovery by analysing hundreds of images taken by Hubble to study how galaxies formed.

"This supernova appears to be one of a special class of explosions that allows astronomers to understand how the universe's expansion has changed over time, much as the way a parent follows a child's growth spurts by marking a doorway," said Riess. "It shows us the universe is behaving like a driver who slows down approaching a red stoplight and then hits the accelerator when the light turns green."

The record-breaking supernova appears relatively bright, a consequence of the Universe slowing down in the past (when the supernova exploded) and accelerating only recently.