Scientists find precise measurement of how brightly the universe glows

The sky is not actually completely dark, scientists say

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Scientists have found the best measurement yet of how much the universe glows.

The universe has what researchers liken to a cosmic night light: a very dim, faint glow that spreads right through the cosmos.

And researchers have now found how bright that is, more precisely than ever before. The light – known as the cosmic optical background – is 100 billion times fainter than the sunlight that reaches the Earth’s surface.

That makes it impossible to see with the naked eye, and very difficult to see even with advanced telescopes. As such, they had to use Nasa’s New Horizons spacecraft, which flew past Pluto in 2015 and is now billions of miles from Earth.

That allowed researchers to get away from the light that surrounds Earth, and which reflects off the dust and debris that is near to our planet. With that, they could get a view deep into the universe.

They were still not totally clear from dust. But they were able to extract that “halo” of light that sits around our galaxy from their calculations and work out the light that is left behind.

That light is the background glow of the universe that was left behind by the trillions of stars and galaxies that have formed and then died since the universe began.

Finding an exact measurement of it is useful because it allows scientists to check whether their accounting of the growth of the universe is correct – or if there are other, unaccounted, sources of light in our universe.

Scientists found that the background is about 11 nanowatts per square meter per steradian. A steradian is a bit of sky about as wide as 130 of our moons.

That is roughly what researchers expected to find. That means there doesn’t seem to be any strange objects – particles or galaxies – that are putting out more light than we had realised.

The work is described in a new paper, ‘New Synoptic Observations of the Cosmic Optical Background with New Horizons’, published in The Astrophysical Journal.