A giant study that looked at more than 200,000 galaxies has measured the energy generated across a large region of space with the highest known accuracy, and determined the universe is slowly dying.

The findings revealed the energy in the observed area of the cosmos is only half of what it was two billion years ago, and is continuing to fade, the International Center for Radio Astronomy Research reported. To make their findings, a team of researchers used seven of the world's most powerful telescopes to look at galaxies at 21 different wavelengths from the far ultraviolet to the far infrared.

"We used as many space and ground-based telescopes 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 ICRAR Professor Simon Driver, who presented the findings at the International Astronomical Union's General Assembly in Honolulu.

All of the energy in the universe was created in the Big Bang, but some remains in stuck within the form of mass. Stars shine by converting this mass into energy, which is described in Albert Einstein's famous E=MC2 equation.

"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," Driver said. "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."

Researchers have known the energy in the universe has been declining since the 1990s, but this recent study outlines the phenomenon across all wavelengths.

"The Universe is fated to decline from here on in, like an old age that lasts forever. The Universe has basically plonked itself down on the sofa, pulled up a blanket and is about to nod off for an eternal doze," Driver concluded.

The findings were published in a recent edition of the journal Monthly Notices of the Royal Astronomical Society and the study is part of the Galaxy and Mass Assembly (GAMA) project.