THE universe is far more transparent at high energies than we thought. This discovery - based on sightings of unexpectedly bright objects that should be too far away to see so clearly - may call into question our understanding of how galaxies are born and evolve.
Most light travels through the cosmos unimpeded. But photons with very high energies of more than 100 gigaelectronvolts can collide with intergalactic infrared light. The longer these photons have to travel, the greater their chances of colliding and the less likely they are to reach Earth. As a result, distant blazars - galaxies with gluttonous black holes at their centres whose flares are pointing directly at Earth - are supposed to be much dimmer at higher energies than those that are not so far off.
Based on estimates of the amount of infrared light pervading the universe, blazars more than a billion years old ...
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