Scientists calculate how much starlight the universe has ever produced

'This has never been done before'

Many of the articles in Sky & Telescope are written by professional astronomers (Pete Martin / Clemson University)

Scientists have worked out how much starlight our universe has ever produced.

The answer – which roughly translates to an awful lot – could illuminate some of the most profound mysteries about the cosmos.

Stars first started forming soon after our universe began, roughly 14 billion years ago. Ever since, it has got far more efficient in producing them, going on to create about a trillion-trillion stars that sit in two trillion galaxies.

Now scientists have worked out for the first ever time just how those stars formed, and how much light has been emitted over that vast time period.

They did so using data from Nasa's Fermi Gamma-ray Space Telescope, which gives a picture of the light that is swirling deep in the universe.

"From data collected by the Fermi telescope, we were able to measure the entire amount of starlight ever emitted. This has never been done before," said astrophysicist Marco Ajello​, who is lead author of the paper. "Most of this light is emitted by stars that live in galaxies. And so, this has allowed us to better understand the stellar-evolution process and gain captivating insights into how the universe produced its luminous content."

The calculations allowed scientists to work out the total number of photons ever emitted.

Expressing the number they found is very difficult, in part because it relies on a number of variables. But it is also literally difficult to write out, because there are so many zeroes.

In all, there have been four and then 85 zeroes of them.

Despite that vast amount of light ever emitted, very little of it ever gets to us beyond the light we see from our own sun and galaxy. The brightness of the universe as it reaches us is roughly equivalent to looking at a 60-watt lightbulb in complete darkness, from 2.5 miles away.

That is because the universe is so vast and distant. But the Fermi telescope allowed the researchers to look at the dim swirl of light that comes from stars, and in so doing calculate how much light was being absorbed and therefore how much there might ever have been around.

The new discovery will now allow scientists to peek out into the very beginnings of the universe.

"The first billion years of our universe's history are a very interesting epoch that has not yet been probed by current satellites," Ajello said. "Our measurement allows us to peek inside it. Perhaps one day we will find a way to look all the way back to the Big Bang. This is our ultimate goal."