The brightest galaxy in the Universe
It’s called WISE J224607.57-052635.0 and a remote galaxy whose brightness record is equal to that produced by 300 trillion Suns. It was discovered by the NASA satellite, WISE and belongs to a new class of objects called ultra-luminous infrared galaxies. According to the authors of this study, published in the Astrophysical Journal, the super bright object may contain at its core a supermassive black hole that is supplying a higher quantity of matter than that which is allowed.
Thanks to a series of observations made with NASA satellite WISE (Wide-field Infrared Survey Explorer) astronomers have discovered a distant galaxy whose light is really at least as 300 trillion Suns. It is the brightest galaxy that has ever been observed until now, it belongs to a new class of objects that were recently identified by WISE, i.e. ultra-bright infrared galaxies or ELIRGs (Extremely Luminous InfraRed Galaxies).
“What we are seeing is a very intense phase of galactic evolution,” says Chao-Wei Tsai’s Jet Propulsion Laboratory (JPL) of NASA and lead author of the study published in the Astrophysical Journal. “This light so bright it could be caused by the intense activity of the central black hole.” Known by the acronym WISE J224607.57-052635.0, super bright galaxy could, in fact, contain a supermassive black hole at its core that is supplying gas at a high rate. We know that supermassive black holes capture the gas and matter from an accretion disk around them. This accretion process does raise the temperature of the disc up to millions of degrees with consequent emission of high-energy radiation which is manifested in the form of visible light, ultraviolet and X-rays addition, the radiation is blocked by a series of “cocoons” dust surrounding and when it is heated emits infrared light.
The black holes of large size are very common in galactic nuclei, but to find one so big and so far is a very rare case. Since the light has traveled for about 12.5 billion years to reach our detectors, astronomers are observing the object as it was in the past. Its black hole had a mass of billions of times the Sun already had at the time when the Universe had an age equal to one tenth of the current (13.8 billion years).
In their article, the authors highlight three basic hypotheses that may explain why the black holes of this particular category of ultra-luminous infrared galaxies evolve so that it becomes so massive. The first idea is based on the fact that the black holes are born already big. In other words, the black holes in infancy may be much larger than assumed. “How do I get, for example, an elephant?” asks Peter Eisenhardt of WISE project scientist and co-author of the study. “Perhaps, one way would be to start from a baby elephant.”
The other two cases concern, however, the breach of a theoretical limit known as the Eddington limit. In the process of accretion of matter, the gas falls toward the black hole heats by emitting radiation. In turn, the radiation pressure hinders the gas, moving it away, and this sets a limit to the rate at which a black hole is able to continuously attract the surrounding matter. If this limit is breached, the black hole can, in principle, increase its size at a dizzying pace. In general, they have already been observed in cases where the black holes violate this limit but that of this study would have repeatedly violated to become bigger and bigger.
The third alternative is based on the fact that the black holes could somehow get around this limit. “Another way that a black hole can become so great is to assume that it is fed at a rate very high, more than he is allowed,” says Tsai. “This can happen if the black hole does not rotate so fast.” “If a black hole rotates slowly enough, not so much reject his” meal “and eventually will capture more material than a black hole spins faster. The massive black holes that we find in ultra-bright infrared galaxies could feed a larger amount of material for a longer period,” adds Andrew Blain of the University of Leicester and co-author of the study. “It’s a bit like winning a competition to see who eats the most hot dogs but on a time interval of a few hundred million years.”
In 2010, WISE has already enabled us to identify several objects “extravagant” in images taken over the entire sky. Therefore, observing the whole sky with a sensitivity better the NASA satellite has been able to capture these rare cosmic samples that otherwise would not have been revealed. This study reports a total of 20 new ultra luminous infrared galaxies, including WISE J224607.57-052635.0 which is the brightest so far identified. These objects have not been revealed before being are too distant but also because the powder transforms their intense visible light in an extraordinary emission of infrared radiation. “In another study carried out always with WISE, we found that about half of very bright galaxies are seen very well in the infrared,” concluded Tsai.
Certainly more data are needed to solve the riddle of this particular class of galaxies. The next step now will be to accurately determine the mass of the central black holes. In fact, know more about their physical parameters will allow researchers to study their evolution, as well as that of other galaxies, in this crucial chapter of cosmic history.