Analysis of starlight from more than 220,000 distant galaxies shows that the cosmos has lost half of its brightness in the past two billion years

Without applause or encore, the lights are going out across the universe, as old stars die faster than new ones are born to replace them.

Astronomers described the slow death of the cosmos in fresh detail on Monday after training some of the world’s most powerful telescopes on a vast region of space.



They analysed starlight from more than 220,000 distant galaxies and found that the universe has lost about half of its twinkle over the past two billion years. It will lose far more in the next two billion.

“The universe is curling up on the sofa and becoming a couch potato,” said Joe Liske, an astronomer at the European Southern Observatory in Garching, Germany, who took part in the study.



Universal dimming is driven by a slump in the rate of new star formation, which peaked about eight billion years ago. Stars shine by fusing hydrogen into helium, but as they consume their cosmic fuel supply, the birth rate of new stars falls dramatically.



A simulated fly-through of the universe as catalogued by the GAMA project, showing the real positions and images of the galaxies that have been mapped so far.

The fading will play out over billions of years, until the universe glows only faintly with a smattering of stars. “It’s not that we can define a point in the future when the universe goes out. A very small amount of activity will continue for billions of years,” Liske said.

The international team used land and space-based telescopes to observe an area of the sky the size of 1000 full moons. They measured light coming from galaxies as near as 500 million light years and as distant as several billion light years away.

The researchers then analysed the light at different wavelengths, ranging from the ultraviolet through to visible and the infra-red. By analysing starlight across so many wavelengths, they could calculate the rate of dimming more accurately than before. The latest measurements, for example, take account of dust particles in space that absorb visible light from stars and re-radiate it in the infra-red.

“We’ve been able to measure quite precisely how fast this dimming is proceeding,” Liske said. “It’s a piece of the puzzle in the history of the universe that reaches all the way back to the Big Bang.”



Far out, man: 13.1bn-year-old galaxy is most distant yet seen by humans Read more

The astronomers worked out the brightness of enormous cubes of space measuring one million light years on each side. The youngest cubes of space, about half a billion years old, glowed with the luminosity of 11 million suns, but the oldest, about 2.5 billion years old, were as bright as 19 million suns, said Will Sutherland, an astronomer at Queen Mary, University of London.

The dimming is exacerbated by the accelerating expansion of the universe, which is throwing material apart at an ever-increasing speed.



The results, part of the Galaxy and Mass Assembly (GAMA) project, drew on observations from a host of instruments, including Nasa’s Galex and Wise space telescopes, the European Southern Observatory’s Vista telescope in Chile, and the Anglo-Australian telescope at Siding Spring Observatory in New South Wales. The findings were presented at an International Astronomical Union meeting in Honolulu on Monday.



“The universe is not going to go black any time soon,” said Sutherland. “But it’ll fade. And then what you’re left with is little old red stars that shine away for a long time more.”

