A group of astronomers studying more than 221,000 galaxies has measured the energy generated within a large portion of space more precisely than ever before, discovering that it’s only half what it was two billion years ago and fading.

Their study, which is part of the Galaxy And Mass Assembly (GAMA) project, the largest multi-wavelength survey ever put together, involved many of the world’s most powerful telescopes, including ESO’s VISTA and VST survey telescopes at the Paranal Observatory in Chile, NASA’s orbiting telescopes GALEX and WISE, and ESA’s Herschel Space Observatory.

“We used as many space and ground-based telescopes as we could get our hands on to measure the energy output of over 200,000 galaxies across as broad a wavelength range as possible,” said team leader Prof Simon Driver from the University of St Andrews, UK, and ICRAR.

The survey data, released to scientists around the world today, includes measurements of the energy output of each galaxy at 21 wavelengths, from the ultraviolet (UV) to the far infrared (IR). This dataset will help them to better understand how different types of galaxies form and evolve.

All energy in the Universe was created in the Big Bang with some portion locked up as mass. Stars shine by converting this mass into energy as described by Einstein’s famous equation E=mc2.

The GAMA study sets out to map and model all of the energy generated within a large volume of space today and at different times in the past.

“While most of the energy sloshing around was created in the aftermath of the Big Bang, additional energy is constantly being released by stars as they fuse elements like hydrogen and helium together,” said Prof Driver, who is the first author of a paper submitted for publication in the Monthly Notices of the Royal Astronomical Society.

“This newly released energy is either absorbed by dust as it travels through the host galaxy, or escapes into intergalactic space and travels until it hits something such as another star, planet, or very occasionally a telescope mirror.”

The fact that the Universe is slowly fading has been known since the late 1990s, but this study shows that it is happening across all wavelengths from the UV to the IR.

“The Universe will decline from here on in, sliding gently into old age. The Universe has basically sat down on the sofa, pulled up a blanket and is about to nod off for an eternal doze,” Prof Driver said.

Prof Driver and co-authors hope to expand the work to map energy production over the entire history of the Universe, using a swathe of new facilities, including the Square Kilometre Array, the world’s largest radio telescope, which is due to be built in Australia and South Africa over the next decade.

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Simon P. Driver et al. 2015. Galaxy And Mass Assembly (GAMA): Panchromatic Data Release (far-UV—far-IR) and the low-z energy budget. MNRAS, submitted for publication