The next time you get a little color after a day of fun under the sun, be sure to also give a little nod to some extra-galactic photons. According to a new study published in The Astrophysical Journal, our bodies are constantly pummeled by radiation from beyond the Milky Way.
"Most of the photons of light hitting us originate from the Sun, whether directly, scattered by the sky, or reflected off dust in the Solar System," astrophysicist Simon Driver of the International Centre for Radio Astronomy Research (ICRAR) said. "However, we're also bathed in radiation from beyond our galaxy, called the extra-galactic background light."
The study, which measured the light hitting the Earth from outside our galaxy over a very broad wavelength range, determined that lying under the open sky will result in roughly "sextillion photons of light per second" hitting your body. Of that massive number, about 10 billion photons per second originate from extra-galactic sources. Most traveled for billions of years through space before hitting your skin.
While alien photons sound alarming, Driver is quick to point out that it would take trillions of years of basking in extra-galactic radiation for there to be any detrimental effects. In contrast, the American Skin Association warns that most people suffer skin damage from the sun's ultraviolet light after only 20 minutes of exposure.
Driver's research comes as part of his work with the Galaxy and Mass Assembly (GAMA) survey, a catalog of 300,000 nearby galaxies. To accurately measure extra-galactic background light, the team sourced data from an array from of space-based instruments including NASA’s Galaxy Evolution Explorer and Wide-field Infrared Survey Explorer telescopes, the Spitzer and Hubble space telescopes, and the European Space Agency’s Herschel space observatory.
By studying the various wavelengths present in space, Driver and his team are hopeful they can better understand how galaxies form.
"The problem is that galaxies are so complicated, you’ve got hot and cold gas, dust, stars and dark matter and it’s the interplay of these components that leads to galaxy evolution," he said. "To look at that you have to look across the full wavelength range and that’s never been done on such a large scale until now."
For an incredible look at GAMA's survey to date, check out the simulated fly-through below showing the real positions and images of galaxies mapped so far. According to ICRAR, the proportion of sky that's in this video is very small — 60 square degrees, "or just 0.14% of the whole sky."