Galaxy survey to probe why the universe is accelerating

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June 30, 2015 by Bill Johnson

Galaxy survey to probe why the universe is acceleratingWe know that our universe is expanding at an accelerating rate, but what causes this growth remains a mystery. The most likely explanation is that a strange force dubbed “dark energy” is driving it. Now a new astronomical instrument, called the Physics of the Accelerating Universe Camera (PAUCam), will look for answers by mapping the universe in an innovative way.

The camera, which will record the positions of around 50,000 galaxies at once, could also shed light on what dark matter is and how the cosmos evolved.

In the 1990s, astronomers studying exploding stars – supernovae – in galaxies far away discovered that the universe’s expansion was accelerating. This came as surprise, as scientists at the time thought it was slowing down. With no obvious solution at hand, scientists argued that there must be some sort of mysterious force – dark energy – pulling the universe apart.

Fast forward about two decades and we still don’t know what dark energy is, thought to make up 71% of all the energy in the universe. One theory says it can be explained by an abandoned version of Einstein’s theory of gravity – known as the “cosmological constant” – which is a measure of the energy density of the vacuum of space. Another argues that it is caused by enigmatic scalar fields, which can vary in time and space. Some scientists even believe that a weird “energy fluid” that fills space could be driving the expansion.
Mapping the sky

Of course, the only way to find out is through observation. After spending six years under design and construction by a consortium of Spanish research institutions, PAUCam was successfully tested out for the first time this month – seeing “first light” on the 4.2 metre William Herschel Telescope on La Palma in the Canary Islands.

Using the information captured by PAUCam, an international team, including researchers from Durham University’s Institute for Computational Cosmology, is being set up to build a unique map of how galaxies are arranged in the universe.

Read more: Galaxy survey to probe why the universe is accelerating


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