Astronomers have long used terms like “ultra” and “hyper” to describe just how luminous the brightest galaxies in the universe truly are, but eight new galaxies discovered by researchers at the University of Massachusetts Amherst take it up a notch.
The UMass team, led by senior undergraduate student Kevin Harrington, and an international group team of colleagues used the 50-meter diameter Large Millimeter Telescope in Mexico to discover galaxies so bright that no current terminology accurately describes them.
“We’ve taken to calling them ‘outrageously luminous’ among ourselves, because there is no scientific term to apply,” Harrington explained in a statement. An ultra-luminous galaxy has a rating of one trillion solar luminosities, and a hyper-luminous one reaches levels of close to 10 trillion solar luminosities, he said. The new galaxies top 100 trillion solar luminosities.
The eight galaxies are believed to be approximately 10 billion years old, meaning that they were formed just four billion years after the Big Bang, according to the authors. A study detailing their findings has been published online by the Monthly Notices of the Royal Astronomical Society.
These galaxies are so bright they defy current naming conventions. Credit: K.C. Harrington et al.
Galaxies appear brighter from Earth due to gravitational lensing
Using the Large Millimeter Telescope (LMT), a device that is said to be the largest and the most sensitive single-aperture instrument of its kind on Earth, as well as space-based telescopes and a cosmology experiment on the NASA/ESA collaboration Planck satellite, they were able to detect the glow of the Big Bang and observe the newfound galaxies for the first time.
UMass astronomy professor Min Yun, Harrington’s advisor and a co-author on the new study, noted that galaxies such as these “were not predicted by theory to exist; they’re too big and too bright, so no one really looked for them before.”
“Knowing that they really do exist and how much they have grown in the first 4 billion years since the Big Bang helps us estimate how much material was there for them to work with,” the professor added. “Their existence teaches us about the process of collecting matter and of galaxy formation. They suggest that this process is more complex than many people thought.”
The researchers note that, despite their extreme brightness, these galaxies are not as large as they first appear. Follow-up research revealed that their high luminosity levels are partially due to the phenomenon known as gravitational lensing, which causes light passing close to massive objects to become magnified and appear brighter. In this case, Yun said, gravitational lensing causes the galaxies to appear to be 10 times brighter than they really are when viewed from Earth.
He also emphasized that gravitational lensing of a distant galaxy by another galaxy is a rather rare phenomenon, and that finding up to eight potentially lensed objects during the course of the study “is another potentially important discovery.” Harrington added that findings gravitational lensing is like finding a needle in a haystack, but “finding lensed sources this bright is as rare as finding the hole in the needle in the haystack.”
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Messier 81 is an example of a known bright galaxy, although it isn’t an example of a new “outrageously bright” galaxy. Image credit: NASA
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