Spooky alignment of quasar axes across billions of light-years with large-scale structure

November 21, 2014

This artist’s impression shows schematically the mysterious alignments between the spin axes of quasars and the large-scale structures that they inhabit that observations with ESO’s Very Large Telescope have revealed. These alignments are over billions of light-years and are the largest known in the Universe. The large-scale structure is shown in blue and quasars are marked in white with the rotation axes of their black holes indicated with a line around them. This picture is for illustration only and does not depict the real distribution of galaxies and quasars. (Credit: ESO/M. Kornmesser)

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.

Quasars are galaxies with very active supermassive black holes at their centers. 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.

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.

Artist’s rendering of ULAS J1120+0641, a very distant quasar powered by a black hole with a mass two billion times that of the Sun (credit: ESO/M. Kornmesser)

“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 new VLT results also indicate that the rotation axes of the quasars tend to be parallel to the large-scale structure in which they find themselves — a cosmic web of filaments and clumps around huge voids where galaxies are scarce.

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%.

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)

“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,” adds Dominique Sluse of the Argelander-Institut für Astronomie in Bonn, Germany and University of Liège.

The team could not see the rotation axes or the jets of the quasars directly. Instead they measured the polarization of the light from each quasar and, for 19 of them, found a significantly polarized signal. The direction of this polarization, 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,” concludes Sluse.


Abstract of Alignment of quasar polarizations with large-scale structures

We have measured the optical linear polarization of quasars belonging to Gpc-scale quasar groups at redshift z ∼ 1.3. Out of 93 quasars observed, 19 are significantly polarized. We found that quasar polarization vectors are either parallel or perpendicular to the directions of the large-scale structures to which they belong. Statistical tests indicate that the probability that this effect can be attributed to randomly oriented polarization vectors is of the order of 1%. We also found that quasars with polarization perpendicular to the host structure preferentially have large emission line widths while objects with polarization parallel to the host structure preferentially have small emission line widths. Considering that quasar polarization is usually either parallel or perpendicular to the accretion disk axis depending on the inclination with respect to the line of sight, and that broader emission lines originate from quasars seen at higher inclinations, we conclude that quasar spin axes are likely parallel to their host large-scale structures.