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Brightest galaxy in the universe discovered

Scientists have discovered the brightest galaxy in the universe, one so luminous it would outshine 300 trillion suns.

Known as WISE J224607.57-052635.0, this beacon in the universe may have a behemoth black hole at its belly, gorging itself on gas.

"We are looking at a very intense phase of galaxy evolution," said Chao-Wei Tsai of NASA's Jet Propulsion Laboratory in Pasadena, California, lead author of a new report appearing in the Friday issue of The Astrophysical Journal. "This dazzling light may be from the main growth spurt of the galaxy's black hole."

The galaxy was spotted using data from NASA's Wide-field Infrared Survey Explorer (WISE). The galaxy belongs to a new class of objects recently discovered by WISE - appropriately named extremely luminous infrared galaxies, or ELIRGs. In their paper, the scientists said they have found 20 new ELIRGs, including the most luminous galaxy found to date.

Supermassive black holes draw gas and matter into a disk around them, heating the disk to roaring temperatures of millions of degrees and blasting out high-energy, visible, ultraviolet and X-ray light.

That light is blocked by surrounding cocoons of dust. As the dust heats up, it radiates infrared light. The conversion of visible light into infrared explains why these galaxies were not found earlier.

Immense black holes are common at the cores of galaxies, but finding one this big so "far back" in the cosmos is rare. Because light from the galaxy hosting the black hole has traveled 12.5 billion years to reach us, astronomers are seeing the object as it was in the distant past. The black hole was already billions of times the mass of our sun when our universe was only a tenth of its present age of 13.8 billion years.

There are several reasons why black holes in these ELIRGs may have grown so big. They probably started out big and then involved either breaking or bending the theoretical limit of black hole feeding, called the Eddington limit.

When a black hole feeds, gas falls in and heats up, blasting out light. The pressure of the light actually pushes the gas away, creating a limit to how fast the black hole can continuously swallow 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. This one, however, 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," Tsai said. "This can happen if the black hole isn't spinning that fast."

"The massive black holes in ELIRGs could be gorging themselves on more matter for a longer period of time," said Andrew Blain of University of Leicester in the United Kingdom, a co-author of this report. "It's like winning a hot-dog-eating contest lasting hundreds of millions of years."

Going forward, the team is hoping to better determine the masses of the central black holes. Knowing these objects' true hefts will help reveal their history, as well as that of other galaxies.