Using NASA’s Wide-field Infrared Survey Explorer (WISE), astronomers have catalogued 20 previously undetected galaxies that are so bright they belong to an entirely new class of objects, including one that releases 10,000 times more energy than the Milky Way — even though it’s smaller.
Two decades ago, astronomers first described “hyperluminous infrared galaxies,” or HyLIRGs. These galaxies shine as bright as 10 trillion Suns (1013 L☉ where 1 L☉ is equal to the luminosity, or solar flux, of our Sun). But as a new paper published in the May 22 issue of The Astrophysical Journal now shows, there are galaxies even brighter than HyLIRGs. Called “extremely luminous infrared galaxies,” or ELIRGs, they’re as bright as 100 trillion Suns (1014 L☉) or more.
The new study, led by Chao-Wei Tsai of NASA’s Jet Propulsion Laboratory, describes 20 previously unseen ELIRGs, including what is now considered the brightest-known galaxy in the Universe. These extremely luminous galaxies were not found earlier owing to their extreme distance from the Earth, and because they feature thick layers of dust that converts their visible light into infrared. Thanks to WISE, these galaxies have finally come into view.
The brightest of the newly discovered galaxies, called WISE J224607.57-052635.0, is located 12.5 billion light-years away. Its luminosity has been measured at a jaw-dropping 3x1014 L☉, which is as bright as 300 trillion Suns. At its center is a particularly large and voracious supermassive black hole that’s gorging itself on gas. The resulting orbital disk is soaring at temperatures of millions of degrees, sending out bursts of high-energy, visible, ultraviolet, and X-ray light. All this light is smashing against a layer of dust that, after getting heated up, radiates detectable infrared red light.
The researchers have posited three theories to explain the presence of ELIRGs.
First, these bright galaxies may be born that way, which would suggest that embryonic black holes might be bigger than we assumed.
Alternately, the supermassive black holes resident at the core of the galaxies are either bending or breaking the theoretical limit of black hole feeding. A NASA release explains:
The pressure of the light actually pushes the gas away, creating a limit to how fast the black hole can continuously scarf down matter. If a black hole broke this limit, it could theoretically balloon in size at a breakneck pace. Black holes have previously been observed breaking this limit; however, the black hole in the study would have had to repeatedly break the limit to grow this large.
Alternatively, the black holes might just be bending this limit.
“Another way for a black hole to grow this big is for it to have gone on a sustained binge, consuming food faster than typically thought possible,” said Tsai. “This can happen if the black hole isn’t spinning that fast.”
If a black hole spins slowly enough, it won’t repel its meal as much. In the end, a slow-spinning black hole can gobble up more matter than a fast spinner.
As study co-author Andrew Blain of the University of Leicester in the United Kingdom put it: “It’s like winning a hot-dog-eating contest lasting hundreds of millions of years.”
More research will be required to solve this intriguing celestial mystery.
Read the entire study at the pre-print arXiv: “The Most Luminous Galaxies Discovered by WISE”.