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Most luminous galaxy in the universe

This galaxy is very distant. It shines with a luminosity of some 300 trillion suns. It’s one of a new class of objects discovered via NASA’s WISE mission.

View larger. | Artist's concept via NASA

View larger. | Artist’s concept of the most luminous galaxy via NASA

NASA said today (May 21, 2015) that its WISE mission has discovered a remote galaxy shining with the light of more than 300 trillion suns. That makes this galaxy the most luminous one found to date. Chao-Wei Tsai of NASA’s Jet Propulsion Laboratory in Pasadena, California is lead author of this study, which appears in the May 22 issue of The Astrophysical Journal. He said in a statement that the galaxy’s great luminosity is likely linked to its central, supermassive black hole:

We are looking at a very intense phase of galaxy evolution. This dazzling light may be from the main growth spurt of the galaxy’s black hole.

WISE – the Wide-field Infrared Survey Explorer – has the job of scanning the entire sky in infrared light. Thus this galaxy was seen in the infrared, not in visible light. WISE astronomers have recently discovered a whole new class of objects like this galaxy, which they are calling extremely luminous infrared galaxies, or ELIRGs. The new study reports a total of 20 new ELIRGs, including the most luminous galaxy. Why didn’t astronomers find these galaxies sooner? It’s because they are extremely far away. What’s more, dust converts their powerful visible light into an incredible outpouring of infrared light.

The most luminous galaxy is known to astronomers as WISE J224607.57-052635.0. It’s some 12.5 billion years away, existing at a time when the universe was only one-tenth of its present age. Many, if not most, galaxies are thought to have supermassive black holes at their cores. We might be seeing this galaxy at a time when its black hole is gorging itself on its galaxy’s gas. NASA said:

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. The light is blocked by surrounding cocoons of dust. As the dust heats up, it radiates infrared light.

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The new study outlines three reasons why the black holes in the ELIRGs might have grown so massive.

First, these astronomers say, the black holes might have been born big. In other words, the “seeds,” or embryonic black holes, might be bigger than thought possible. Peter Eisenhardt, project scientist for WISE at JPL and a co-author on the paper, said:

How do you get an elephant? One way is start with a baby elephant.

There are other two explanations. They both involve either breaking or bending the theoretical limit of black hole feeding, called the Eddington limit. NASA said:

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 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.

The other alternative is that the black holes might just be bending this limit. Tsai said:

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.

This can happen if the black hole isn’t spinning that fast.

In other words, NASA said, 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 always, the astronomers say, more research is needed to solve the puzzle of dazzlingly luminous galaxies.

Read more from NASA

Artist's concept of WISE, the Wide-field Infrared Survey Explorer. Image via NASA/JPL-Caltech

Artist’s concept of WISE, the Wide-field Infrared Survey Explorer. Image via NASA/JPL-Caltech

Bottom line: A galaxy known as WISE J224607.57-052635.0 is the most luminous galaxy found to date.

Deborah Byrd

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