New observations with ESO’s Very Large Telescope (VLT) in Chile have revealed alignments over the largest structures ever discovered in the Universe. A European research team has found that the rotation axes of the central supermassive black holes in a sample of quasars are parallel to each other over distances of billions of light-years. The team has also found that the rotation axes of these quasars tend to be aligned with the vast structures in the cosmic web in which they reside. A team led by Damien Hutsemékers from the University of Liège in Belgium used the FORS instrument on the VLT to study 93 quasars that were known to form huge groupings spread over billions of light-years, seen at a time when the Universe was about one third of its current age. "Alignments between galaxy axes and large-scale structures are expected in theories of structures and galaxy formation. The alignments between quasar axes and large-scale structures are found on much larger scales so that it is a bit mysterious and a challenge for the theory," Hutsemékers told astrowatch.net. The research was presented in a paper entitled “Alignment of quasar polarizations with large-scale structures“, by Damien Hutsemékers et al., to appear in the journal Astronomy & Astrophysics on 19 November 2014.
Quasars are galaxies with very active supermassive black holes at their centres. These black holes are surrounded by spinning discs of extremely hot material that is often spewed out in long jets along their axes of rotation. Quasars can shine more brightly than all the stars in the rest of their host galaxies put together.
“The first odd thing we noticed was that some of the quasars’ rotation axes were aligned with each other — despite the fact that these quasars are separated by billions of light-years,” said Hutsemékers.
The team then went further and looked to see if the rotation axes were linked, not just to each other, but also to the structure of the Universe on large scales at that time.
"In the case of galaxies, the rotation axes can be aligned due to a torque generated by the gravitational field of the large-scale structures. We expect that a similar mechanism can apply to active galactic nuclei / quasars. But this is to demonstrate," Hutsemékers noticed.
When astronomers look at the distribution of galaxies on scales of billions of light-years they find that they are not evenly distributed. They form a cosmic web of filaments and clumps around huge voids where galaxies are scarce. This intriguing and beautiful arrangement of material is known as large-scale structure.
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| This very detailed simulation of large scale structure was created as part of the Illustris simulation. The distribution of dark matter is shown in blue and the gas distribution in orange. This simulation is for the current state of the Universe and is centered on a massive galaxy cluster. The region shown is about 300 million light-years across. Credit: Illustris Collaboration |
The new VLT results indicate that the rotation axes of the quasars tend to be parallel to the large-scale structures in which they find themselves. So, if the quasars are in a long filament then the spins of the central black holes will point along the filament. The researchers estimate that the probability that these alignments are simply the result of chance is less than 1%.
“A correlation between the orientation of quasars and the structure they belong to is an important prediction of numerical models of evolution of our Universe. Our data provide the first observational confirmation of this effect, on scales much larger that what had been observed to date for normal galaxies,” said Dominique Sluse of the Argelander-Institut für Astronomie in Bonn, Germany and University of Liège.
"The VLT together with FORS is a very efficient instrument to measure the polarization of faint distant objects," said Hutsemékers. "Measuring levels of polarization 10 times smaller than the polarization of the blue sky in daylight for objects who emitted their light more than 9 billion years ago was a challenging task, only possible with FORS2 at the VLT."
The team could not see the rotation axes or the jets of the quasars directly. Instead they measured the polarisation of the light from each quasar and, for 19 of them, found a significantly polarised signal. The direction of this polarisation, combined with other information, could be used to deduce the angle of the accretion disc and hence the direction of the spin axis of the quasar.
“The alignments in the new data, on scales even bigger than current predictions from simulations, may be a hint that there is a missing ingredient in our current models of the cosmos,” Sluse concluded.
"We would like to observe more quasar groups to better characterize the scale at which alignments take place and reinforce the significance of the effect," Hutsemékers added.
The team is composed of D. Hutsemékers (Institut d’Astrophysique et de Géophysique, Université de Liège, Liège, Belgium), L. Braibant (Liège), V. Pelgrims (Liège) and D. Sluse (Argelander-Institut für Astronomie, Bonn, Germany; Liège).
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