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.
Long ago, when the light left this distant supernova, the universe appears to have been slowing down due to the mutual tug
of all the mass in the universe, explained Riess. Billions of years later, when the light left more recent supernovas, the
universe had begun accelerating, stretching the expanse between galaxies and making objects in them appear dimmer.
Hubble's ability to find titanic stellar explosions at these extreme distances is what it takes to confirm this theory that
the universe must have been slowing down before it switched into high gear, said Dr. Anne Kinney, Director of NASA's Origins
program at NASA Headquarters, Washington, DC. Later this year astronauts will install a new camera on Hubble that will give
us 10 times better resolution than the current camera, which will give us even better capability to find answers to grand
cosmic questions like this.
Observations of several distant supernovae by two teams of astronomers in 1998 led to the theory that the universe got the
green light to accelerate when it was half its present age. Astronomers say the new Hubble findings rule out other
explanations.
Shortly afterwards, astronomer Edwin Hubble made the celebrated discovery that the universe was expanding. He assumed that
the universe must be slowing down under gravity and might even come to a halt, leading Einstein later to say that his
cosmological constant was the biggest blunder of his career. Now it appears Einstein was on the right track after all.
The source of the repulsive gravity may be something akin to Einstein's cosmological constant -- referred to as the energy of
the quantum vacuum, a subatomic netherworld pervading space -- or it may be something entirely new and unexpected.
While we don't know what dark energy is we are certain that understanding it will provide crucial clues iuest to
unify the forces and particles in the universe, and that the route to this understanding involves telescopes, not
accelerators, said astrophysicist Michael Turner of the University of Chicago.