Your suntan is truly cosmic. We are not just paying you a compliment, it’s an actual fact. A tiny fraction of the light responsible for darkening your skin originated far beyond our galaxy.
An international team of astronomers was able to accurately measure the extragalactic background radiation that arrives on Earth each day and night. The measurement, published in the Astrophysical Journal, goes from the far-ultraviolet (the damaging dangerous kind) to the far-infrared.
Understanding this background light emission is very important, as it encodes a record of the entire energy production history of the Universe, from the formation of the first stars to the present day. And thanks to the high precision of the measurement, they can tell us that about ten-trillionths of our suntans come from sources beyond the solar system.
"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," said lead author Professor Simon Driver, from the International Centre for Radio Astronomy Research, in a statement. "However, we're also bathed in radiation from beyond our galaxy, called the extragalactic background light. These photons are minted in the cores of stars in distant galaxies, and from matter as it spirals into supermassive black holes."
Infographic explaining where the photons the Earth receives come from. ICRAR/Dan Hutton
Every second, every square meter (11 square feet) is bombarded by 10 billion intergalactic photons. This might seem like a lot, but it is dwarfed by the amount of light we receive directly or indirectly from our star. They are not going to make much difference to your suntan, but they are very precious for astronomers.
The sources of this radiation are either too far away or too faint to be resolved, however this measurement will give us a clue as to how this light was produced.
“The processes which shape and shuffle mass generate vast quantities of energy, dwarfed only by the vastness of space,” continued Driver. “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.”
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