When looking at light from distant galaxies, the very brightest examples are often given labels like "ultra" or "hyper-luminous." Now, astronomers from the University of Massachusetts at Amherst (UMass Amherst) have observed a new set of galaxies for the very first time that are as much as 10 times as luminous as previous findings. The galaxies aren't quite all they seem, however, with their notable appearance a result, at least in part, of a phenomenon known as gravitational lensing.

When astronomers categorize luminous objects in the night sky, if it has a rating of 1 trillion solar luminosities, then it's referred to as "ultra-luminous." Similarly, it it's rated at 10 trillion solar luminosities, it gets the label "hyper-luminous." But the new objects are much brighter, as much as 100 trillion solar luminosities, with the researchers responsible for their discovery dubbing them "outrageously luminous."

The observations were made using a number of instruments, including the Herschel Space Observatory, the Large Millimeter Telescope (LMT), which is the world's largest single dish steerable millimeter installation, and the Planck telescope. The latter was particularly instrumental in making the discoveries possible, with its all-sky coverage allowing the astronomers to spot the objects in the first place, while the higher resolution of Hershel and the LMT allowed their locations to be precisely pinpointed.

The Planck telescope's all-sky coverage allowed the astronomers to spot the objects (artist's impression)(Credit: ESA/C Carreau)

The astronomers estimate that the galaxies are around 10 billion years old, having formed just 4 billion years following the Big Bang. According to the researchers, the galaxies appear so big and bright that no one expected such objects to exist, meaning that the discovery could significantly advance our understanding of galaxy formation.

"Their existence teaches us about the process of collecting matter and of galaxy formation," said the University of Massachusetts at Amherst's Professor Min Yun. "They suggest that this process is more complex than many people thought."

That said, the galaxies aren't quite as massive as they first appear. After initially spotting the objects, the researchers performed follow-up investigations, and discovered the extreme level of brightness is actually, in part, due to a phenomenon known as gravitational lensing, wherein an object sits in the foreground between the point of observation and the galaxy being studied, magnifying the light as it passes.

Even in light of the lensing, which makes the galaxies appear as much as 10 times brighter than they actually are, they're still, by any standard, extremely luminous. Finding so many lensed objects in a single study – a total of eight were discovered – is also very rare, with the researchers equating it to "finding the hole in the needle in the haystack."

Analysis of the recorded data revealed that the brightness is likely due to an astonishingly high rate of star formation. It's not yet known exactly how or why the galaxies are capable of such rapid star birth, though the researchers intending to continue their investigations in the hope of unraveling the mystery.

The researchers published their findings online in the Monthly Notices of the Royal Astronomical Society.

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