Transparent Universe Reveals Hidden Galaxies


Earth Changes Media

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 were expected to be mostly invisible to telescopes looking for very high-energy gamma rays, says astrophysicist Simon Swordy of the University of Chicago.

But in 2006, the HESS telescope in Namibia reported the discovery of two unexpectedly bright blazars that are more than 2 billion years old. What’s more, bright light from a blazar called 3C279, spotted one night in 2007 by the MAGIC telescope on La Palma in Spain’s Canary Islands, survived some 5 billion years of travel. “We can see significantly further than we thought we could,” says Swordy.

The mystery grew last month, when the VERITAS telescope in southern Arizona, following up on observations made by NASA’s orbiting FERMI telescope, reported the discovery of yet another blazar that glows unusually brightly with very high-energy gamma rays. The new source, named 1ES 0502+675, is 4 billion years old. While it is not as distant as the one discovered by MAGIC, it could provide more useful information as it is bright, sits at a well-established distance and has been observed steadily for more than a month.

These blazars suggest that the amount of infrared light between galaxies must be quite low. This infrared background is light left over from star formation processes that occur early in the life of galaxies. We can estimate the background by counting galaxies in deep space, but now astrophysicists are beginning to question these estimates. “The amount of infrared is really right at the minimum you would expect from what we know about star formation and evolution,” says Rene Ong of the University of California, Los Angeles, and spokesperson for VERITAS. “It’s becoming a problem.”

Continued observation of 1ES 0502+675 could help solve the puzzle. “This source could produce better and more reliable constraints on the extragalactic background than any source that has come before,” says Ong.


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