Astronomers have confirmed by a new method one of the saddest stories of the Universe - one day the stars in the sky will all stop twinkling.
As old stars die, new ones are born, but, for billions of years, the rate of star formation has been in decline.
According to recent estimates, there are 10 times more stars in the visible Universe than all the grains of sand on every beach and desert in the world.
The good news is that they should last for a very long time yet. One day, however, the Universe will fade into darkness.
"It'll be thousands of millions of years before you get big changes in the night sky," says the appropriately named Alan Heavens of Edinburgh University, UK.
"The Universe will carry on forever, as far as we know, but eventually all the stars will go out and it will become a very dark and very cold place."
Fossil record
It has been known for many years that the rate of star formation is slowing.
This has been estimated by observing very distant galaxies. The light from these galaxies has taken thousands of millions of years to reach Earth, giving a picture of what they were like when they were very young.
Professor Heavens and colleagues used data from the Sloan Digital Sky Survey, one of the most ambitious astronomical survey projects ever, to get a more complete picture of the history of star formation.
They looked at what they call the "fossil record" of the Universe - the star light from 40,000 nearby galaxies.
Galaxies shine with the combined light of all the stars they contain. When most of the stars are young, blue light from very hot, massive stars predominates.
These blue stars decay relatively quickly and die out, meaning that the light from older populations of stars is dominated by reddish light from the remaining smaller stars.
The astronomers analysed the spectrum of light using a new compression method to cope with the vast amount of information.
It confirms what we already knew - that star formation peaked around six billion years ago, when our own Sun came into being.
Nevertheless, it gives a more accurate, if gloomy, prediction of what the Universe might be like in the distant future.
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