Oldest Galaxy to be Discovered is an Anachronism

September 22, 2015 | Sarah Tse

Hubble eXtreme Deep Field (XDF), 2012
Photo credit: NASA

The most ancient, distant galaxy has been imaged, but there’s one problem: it shouldn’t exist.

Scientists have found the oldest, most distant galaxy yet: EGS8p7 appears to be a mere 600 million years younger than the universe itself. But according to current theories on the history of the universe, this galaxy shouldn’t even exist.

Soon after researchers at Caltech spotted EGS8p7 using the Hubble and Spitzer Telescopes, they set about to determine its approximate age. This is done by examining the amount and spectrum of light radiated by the galaxy and comparing its “redshift” to those of other galaxies. Redshift is a distortion caused by distance akin to the Doppler effect, except it works on light instead of sound. The further away an object is, the redder and dimmer its light appears to the observer. The researchers used a detection device called multi-object spectrometer for infrared exploration (MOSFIRE) to pick up the galaxy’s spectral signature.

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EGS8p7 has a redshift of 8.68, which makes it the most distant galaxy yet to be discovered. When we start dealing with exceptionally distant cosmic objects, light emission and age are linked by the speed of light and the time it takes for an object’s image to reach us across space. Based on this combination of data, this ancient galaxy is approximately 13.2 billion years old. It’s so far away that we’re looking at a snapshot of the galaxy from its infancy, as it first formed.

This takes us back to a time in the universe’s first billion years when it was full of clouds of uncharged hydrogen atoms. A few hundred million years later, young galaxies heated up the hydrogen gas and gave it an electric charge. This boiling, ionized hydrogen created a spectral light signal called the Lyman-alpha line, and it is this signal that gave away the existence of EGS8p7.

But the detection of this Lyman-alpha line is at odds with our current timeline for the universe. The galaxy’s redshift and age indicates that it created this light signature during a phase when there was no medium for light to travel through. 13.2 billion years ago, the universe’s hydrogen gas had yet to become ionized, and these thick clouds would have absorbed the photons making up EGS8p7’s light signal before they had a chance to travel across the light-years towards us. The researchers should not have picked up the signal at all.

Astrophysicists are still fumbling to explain the galaxy’s spectral presence. The authors of the paper speculate that hydrogen ionization occurred in fits and bursts across the universe. EGS8p7 may have contained extraordinarily bright and powerful stars that released strong enough ultraviolet rays to ionize a bubble of hydrogen gas, allowing the galaxy’s light signature to propagate. Further analysis of the data will reveal whether this theory holds, or if astrophysicists need to rewrite their timeline for the infancy of the universe.

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