(NASA/Goddard Space Flight Center) NASA’s Hubble Space Telescope has looked deep into the distant universe and detected the feeble glow of a star that exploded more than nine billion years ago. The sighting is the first finding of an ambitious survey that will help astronomers place better constraints on the nature of dark energy, the mysterious repulsive force that is causing the universe to fly apart ever faster.

(DOE/Lawrence Berkeley National Laboratory) Two teams at the US Department of Energy’s Fermilab and Lawrence Berkeley National Laboratory have independently made the largest direct measurements of the invisible scaffolding of the universe, using the gravitational lensing effect known as “cosmic shear” to build maps of the distribution of dark matter. Their methods show that surveys with ground-based telescopes can measure cosmic shear with enough accuracy to aid in better understanding the mysterious space-stretching effects of dark energy.

(DOE/Lawrence Berkeley National Laboratory) Two teams at the US Department of Energy’s Fermilab and Lawrence Berkeley National Laboratory have independently made the largest direct measurements of the invisible scaffolding of the universe, using the gravitational lensing effect known as “cosmic shear” to build maps of the distribution of dark matter. Their methods show that surveys with ground-based telescopes can measure cosmic shear with enough accuracy to aid in better understanding the mysterious space-stretching effects of dark energy.

(DOE/US Department of Energy) Secretary of Energy Steven Chu today congratulated Saul Perlmutter, a physicist at DOE’s Lawrence Berkeley National Laboratory and a professor of physics at the University of California at Berkeley, for winning the 2011 Nobel Prize in Physics. DOE’s Office of Science has supported Perlmutter’s research efforts at LBNL since 1983 and currently supports supernova surveys and several additional projects studying dark energy.

(Carnegie Institution) Observations of Type Ia supernovae has led to the discovery that the universe is expanding at an accelerating rate and the notion of dark energy. However, astronomers do not know for certain how the explosions take place and whether they all share the same origin. Now, a team of researchers has examine 41 of these objects and concluded that there are clear signatures of gas outflows from the supernova ancestors, which are likely not white dwarfs.

(University of California – Santa Barbara) “Zombie” stars that explode like bombs as they die, only to revive by sucking matter out of other stars. According to an astrophysicist at UC Santa Barbara, this isn’t the plot for the latest 3-D blockbuster movie. Instead, it’s something that happens every day in the universe — something that can be used to measure dark energy.

This is the part of the Universe that the research group ESSENCE has been observing. To the left you see a famous cluster of galaxes, Abell 168 Photo: Peter Challis

Researchers at the University of Copenhagen’s Dark Cosmology Centre at the Niels Bohr Institute have brought us one step closer to understanding what the universe is made of. As part of the international collaboration ESSENCE they have observed distant supernovae (exploding stars), some of which emitted the light we now see more than half the age of the universe ago. Using these supernovae they have traced the expansion history of the universe with unprecedented accuracy and sharpened our knowledge of what it might be that is causing the mysterious acceleration of the expansion of the universe.

Background and outline

At the end of last century astronomers discovered the startling fact that the expansion of our universe is not slowing down, as all our previous understanding of gravity had predicted. Rather the expansion is speeding up. Nothing in conventional physics can explain such a result. It means that either the universe is made up of around 70% ‘dark energy’ (something that has a sort of anti-gravity) or our theory of gravity is flawed.

Now, as part of the international collaboration “ESSENCE”, researchers at the Danish Dark Cosmology Centre have added a new piece to the puzzle. In two papers recently released they detail observations of supernovae (exploding stars) that allow them to trace the expansion history of the universe in unprecedented detail. ESSENCE is an extension of the original team that discovered the acceleration of the universe and these results push the limits of technology and knowledge, observing light from dying stars that was emitted almost half the age of the universe ago. 

In a third paper, led by the Danish team and released this week, the many new theories that have been proposed to explain the acceleration of the universe are critically assessed in the face of this new data. Dr. Jesper Sollerman and Dr. Tamara Davis lead the team who show that despite the increased sophistication in cosmological models over the last century the best model to explain the acceleration remains one that was proposed by Einstein back in 1917. Although Einstein’s reasoning at the time was flawed (he proposed the modification to his theory so it could support a static universe, because in those days everyone ‘knew’ the universe was not expanding, it may be that he was right all along.

Scientific details:

The primary aim of the experiment is to measure the ‘dark energy’ – the ‘thing’ that is causing the acceleration of the universe – to better than 10%. We measure the dark energy’s ‘equation of state’.  This also allows us to check whether our theory of gravity needs modification. So far it looks like our theory is correct and that the strange acceleration of the expansion of the universe can be explained by Einstein’s ‘cosmological constant’.

In modern terms the cosmological constant is viewed as a quantum mechanical phenomenon called the ‘energy of the vacuum’. In other words, the energy of empty space.  It is this energy that is causing the expansion to accelerate. The new data shows that none of the new theories that have been proposed in the last decade are necessary to explain the acceleration. Rather, vacuum energy is the most likely cause and the expansion history of the universe can be explained by simply adding this constant background of acceleration into the normal theory of gravity.

The ESSENCE team includes 38 top researchers from many different countries on four continents.

For further information contact:

Tamara Davis, Astrophysicist, Ph.D.
DARK Cosmology Centre, Niels Bohr Institute, University of Copenhagen,
Phone: +45 3532-5981, tamarad @ dark-cosmology.dk

Jesper Sollerman, Astrophysicist, Ph.D.
DARK Cosmology Centre, Niels Bohr Institute, University of Copenhagen,
Phone: +45 3532-5899, jesper @ astro.su.se