The universe is slowly running out of energy and dying, according to the most complete study ever undertaken of the cosmos' total energy output.
But there's no need to panic quite yet, we still have around a hundred billion years or so before the last stars die, say scientists.
The finding, which is based on an energy survey of over 200,000 galaxies, was presented today by an international team of scientists at the General Assembly of the International Astronomical Union in Honolulu.
So it's rather bleak, I'm afraid. - Simon Driver, International Centre for Radio Astronomy Research
The fact that the universe is slowly fading has been known since the late 1990s, but the new data from the Galaxy and Mass Assembly (GAMA) project shows it's happening across 21 different wavelengths from the ultraviolet to far-infrared.
Today's galaxies are only producing half as much energy as galaxies were two billion years ago, says the project's head Simon Driver of the International Centre for Radio Astronomy Research in Western Australia.
"What we're seeing is that at every single wavelength, the amount of energy being generated today is almost a factor of two less than the amount of energy that was generated two billion years ago," says Driver.
"That tells us that the universe is essentially dying. It's now fading and dwindling and diminishing, and that result is robust regardless of whether dark energy or dark matter is right or wrong, it doesn't depend on any cosmological model."
The researchers calculate the oldest lowest mass stars, which burn through their fuel very slowly, should keep shining for about another 100 billion years.
"So it's rather bleak I'm afraid," says Driver.
Although there's less energy now than in the past, the study found that there are more stars now than at any other time.
"There is more stellar mass now than there ever has been in the past, or ever will be in the future, we're going through a turning point where stars are still forming and stars are dying," says Driver.
"But now we're at the stage where more mass is being lost than is being formed."
Driver and colleagues studied how different types of galaxies form by mapping all the energy generated within a set volume of space.
"Our survey, mapping out sections of the universe, is a lot like ice core drilling samples in Antarctica where the further down you go the more you start to find out about by the conditions of Earth ... 100 million years ago or 200 million years ago," says Driver.
"In this case we're looking at over five billion years and sampling galaxies at different stages. We can look at those galaxies at different time intervals and we can see how the galaxy population is changing over time."
All energy in the universe was created in the Big Bang with some of it locked up as mass.
Galaxies give out different amounts of energy at different wavelengths; young stars shine in the high ultraviolet, older stars in the optical, hot dust shines in the mid-infrared and cold dust shines in the far-infrared.
"So if you really want to measure everything that's out there, all the energy that's coming, you have to measure all these galaxies at all these different wavelengths," says Driver.
However he admits that not enough is known about the strange properties of dark energy to cover all possibilities, nor was the energy contribution from gamma-rays, X-rays and radio waves included in the survey.
Driver hopes to expand the research to map energy production over the entire history of the universe, and include additional observations using new X-ray telescope spacecraft and facilities like the Square Kilometre Array Radio Telescope now being built in Western Australia and South Africa.
The study has been submitted to the Monthly Notices of the Royal Astronomical Society.