Astronomers using two 10-m optical/infrared telescopes at the W. M. Keck Observatory have discovered the first quadruple quasar, catalogued as SDSS J0841+3921.
This image shows the quadruple quasar SDSS J0841+3921 (quasars are indicated by arrows). Image credit: Joseph Hennawi / Fabrizio Arrigoni-Battaia.
The quartet – four active black holes situated in close proximity to one another – resides in one of the most massive structures ever discovered in the distant Universe.
It is surrounded by a giant nebula of cool dense hydrogen gas – which the astronomers dubbed the Jackpot nebula.
The nebula has an extent of one million light-years across and emits light because it is irradiated by the intense glare of the quasars.
“There are several hundred times more galaxies in this region than you would expect to see at these distances,” said Prof Xavier Prochaska of the University of California Santa Cruz, a co-author on the study published in the journal Science.
Given the exceptionally large number of galaxies, this system is likely a protocluster of galaxies. Because the light from this gigantic structure has been traveling for 10 billion years before reaching our planet, the images show the region as it was 10 billion years ago, less than 4 billion years after the Big Bang.
In their search for quasars surrounded by so-called Lyman-α nebulae, Prof Prochaska and his colleagues examined the spectra of 29 quasars to look for signatures of diffuse extended emission characteristic of fluorescing gas.
One of their candidates, SDSS J0841+3921, appeared promising, and was then subjected to detailed observations using Keck telescopes.
In the process of examining the Keck images, the astronomers realized that there was not just one quasar, but four of them embedded in the nebula.
Piecing together all anomalies surrounding SDSS J0841+3921, they tried to understand what appears to be their incredible stroke of luck.
“If you discover something which, according to current scientific wisdom, should be extremely improbable, you can come to one of two conclusions: either you just got very lucky, or you need to modify your theory,” said lead author Dr Joseph Hennawi of the Max Planck Institute for Astronomy.
The astronomers speculate that some physical process might make quasar activity much more likely in specific environments.
One possibility is that quasar episodes are triggered when galaxies collide or merge, because these violent interactions efficiently funnel gas onto the central black hole. Such encounters are much more likely to occur in a dense proto-cluster filled with galaxies, just as one is more likely to encounter traffic when driving through a big city.
“The giant emission nebula is an important piece of the puzzle since it signifies a tremendous amount of dense cool gas,” said Fabrizio Arrigoni-Battaia of the Max Planck Institute for Astronomy, who was involved in the discovery.
On the other hand, given the current understanding of how massive structures in the Universe form, the presence of a giant nebula in a protocluster of galaxies is totally unexpected.
“Our current models of cosmic structure formation based on supercomputer simulations predict that massive objects in the early Universe should be filled with rarefied gas that is about ten million degrees, whereas this giant nebula requires gas thousands of times denser and colder,” said co-author Dr Sebastiano Cantalupo of ETH Zurich.
“Extremely rare events have the power to overturn long-standing theories. As such, the discovery of the first quadruple quasar may force cosmologists to rethink their models of quasar evolution and the formation of the most massive structures in the Universe,” Dr Hennawi concluded.
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Joseph F. Hennawi et al. 2015. Quasar quartet embedded in giant nebula reveals rare massive structure in distant Universe. Science, vol. 348, no. 6236, pp. 779-783; doi: 10.1126/science.aaa5397
