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How to Get an Intergalactic Sun Tan Without Leaving Earth

Ten trillionths of your sun tan is the result of photons made by distant stars and supermassive black holes.
Image: Flickr/ludovic

There are many different ways to get a tan: some people go to the beach, others to a salon, Donald Trump gets dunked headfirst into a vat of orange goop, and still others go out at night to get bombarded by 10 billion intergalactic photons per second.

According to a new study published on Friday in Astrophysical Journal, that is approximately how many photons generated by stars and supermassive black holes outside the Milky Way are colliding with Earth every second of the day and night. While this may sound like a lot, it's only ten trillionths of the sextillion photons that hit your skin every second that are generated by the Sun.


These numbers are so large as to be almost meaningless, so here's what they look like written out:

Photons/second from the Sun: 1,000,000,000,000,000,000,000

Photons/second from intergalactic space: 10,000,000,000

According to the researchers who lead the study however, you're unlikely to improve your farmer's tan by waiting on photons that have spent billions of years crossing the void just to kiss your skin. It would take "trillions" of years before these photons could cause any lasting damage.

Still, the study of this otherworldly radiation, called extragalactic background light, is scientifically valuable.

According to the international team of researchers—who used observations collected by six different astronomical surveys, including NASA's Wide-field Infrared Survey Explorer and the Hubble space telescope, to make the most accurate measure of extragalactic background light ever—the data will help astronomers and cosmologists understand how the universe evolved from a smooth distribution of atoms shortly after the Big Bang to the complicated structures and distributions of mass and energy we see today.

"The processes which shape and shuffle mass generate vast quantities of energy, dwarfed only by the vastness of space," said Simon Driver, an astrophysicist at the International Centre for Radio Astronomy Research.

"The precise physics as to how this energy is released is still not fully understood and work continues to build numerical models capable of explaining the energy that we've now measured."