Your cosmic suntan

Lie on the beach, and your body is bombarded by about sextillion photons of light per second. Most of these photons, or small packets of energy, originate in our sun. But – according to a study published August 12, 2016 in the Astrophysical Journal – a very small fraction have travelled across the universe for billions of years before ending their existence when they collide with your skin.

In the new study, astronomers accurately measured the light hitting the Earth from outside our galaxy over a broad wavelength range. Astrophysicist Simon Driver of Australia’s International Centre for Radio Astronomy Research (ICRAR), who led the study, said that – day and night – we are constantly bombarded by about 10 billion photons per second from intergalactic space when we’re outside. He said in a statement:

We’re bathed in radiation from beyond our galaxy, called the extra-galactic background light.

These faint glimmerings of radiation are minted in the cores of stars in distant galaxies, and from matter as it spirals into supermassive black holes.

The study was part of ICRAR’s ongoing work to understand the evolution of energy, mass and structure in the universe.

Driver and his team measured ambient radiation from the universe, from a wide range of wavelengths, by combining deep images from a flotilla of space telescopes.

He and collaborators from Arizona State University and Cardiff University collated observations from NASA’s Galaxy Evolution Explorer and Wide-field Infrared Survey Explorer telescopes, the Spitzer and Hubble space telescopes, the European Space Agency’s Herschel space observatory and Australia’s Galaxy And Mass Assembly survey to make what these researchers say is:

… the most accurate measurements ever of the extra-galactic background light.

While 10 billion photons a second might sound like a lot, Driver said we would have to bask in it for trillions of years before it caused any long-lasting damage.

Rogier Windhorst, from Arizona State University, said the universe also comes with its own inbuilt protection as about half the energy coming from the ultraviolet light of galaxies is converted into a less damaging wavelength by dust grains. He said:

The galaxies themselves provide us with a natural suntan lotion with an SPF of about two.

Bottom line: We’re bathed in radiation from beyond our galaxy, called the extra-galactic background light.