A galaxy has been discovered that is brighter than the light of 300 trillion suns. Suffice to say, this galaxy is the brightest in the universe. But how can anything get so luminous?
NASA's Wide-field Infrared Survey Explorer (WISE) discovered this bright object. The galaxy, with the catchy name 'WISE J224607.57-052635.0,' turns out to be a bit of a head-scratcher. Despite being a whopping 12.5 billion light-years away, meaning that the signals WISE picked up took 12.5 billion years to reach us, it's extraordinarily luminous. It is highly unusual for an object so young in the universe's history to be so bright.
"We are looking at a very intense phase of galaxy evolution," said Chao-Wei Tsai of NASA's Jet Propulsion Laboratory (JPL) and lead author on the report. "This dazzling light may be from the main growth spurt of the galaxy’s black hole."
Black holes grow by gravitationally attracting dust and matter. The dust gets hotter as it gets "eaten" by the black hole, so it releases some of this increasing heat energy as light, mostly in the infrared region of the spectrum. These are the photons that we detect with WISE. For a black hole to create this much light, it would have to be enormous and therefore guzzling gas and dust at an alarming rate—much faster than what we've witnessed before now.
"The massive black holes in ELIRGs (extremely luminous infrared galaxies) could be gorging themselves on more matter for a longer period of time," said Andrew Blain of University of Leicester, a co-author of the report. "It's like winning a hot-dog-eating contest lasting hundreds of millions of years."
There are a couple of theories about how exactly this black hole got to be so bright.
One theory suggests that black hole 'seeds' are a lot bigger than we previously thought. "How do you get an elephant?" asked Peter Eisenhardt, project scientist for WISE at JPL and co-author on the paper. "One way is start with a baby elephant." What Eisenhardt is getting at is that this black hole might be big because it was born big.
The other theories start to break a couple of laws of physics. There is a law that dictates how much a black hole can eat, called the Eddington limit. This rule states that when a black hole reaches a certain size, the pressure of the light that its disk produces pushes away incoming dust or 'food.' A few black holes have been known to break this rule on occasion and guzzle a bit more than they're supposed to, but this galaxy would have to have thrown away the rule book for its entire life to reach its enormous size.
"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." This final reason means that the black hole can bypass the Eddington limit if it lives a laid-back existence.