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Spooky alignments of galaxies detected

Nov. 20, 2014
Courtesy of ESO
and World Science staff

New ob­serva­t­ions sug­gest that ga­lax­ies align with each oth­er across vast reaches of space—in a man­ner that as­tro­no­mers had ex­pected, but more so, a re­port said.

The work in­di­cates that over dis­tances of bil­lions of light-years, cer­tain types of super-bright ga­lax­ies tend to spin along the same ax­is. A light-year is the dis­tance light trav­els in a year. 

An image from a si­mula­tion of cos­mic struc­ture show­ing fi­la­ments, sheets and clumps. (Cre­dit: Il­lust­ris Col­la­bor­a­tion)


As­tro­no­mers at­trib­ute the alignments to char­ac­ter­is­tics of the large-scale “cos­mic web,” in which ga­lax­ies overall tend to group them­selves in­to a struc­ture that re­sem­bles a kind of web stretch­ing out in all di­rec­tions. 

A clos­er look at this web re­veals count­less ga­lax­ies ar­ranged along struc­tures that can be de­scribed as fil­a­ments, sheets and clumps. 

The di­rec­tion of the gal­ax­y’s spin ax­is, ac­cord­ing to the new find­ings, of­ten fol­lows a fil­a­ment that the galaxy in­hab­its. 

Pre­vi­ous stud­ies had de­tected si­m­i­lar sorts of alignments for nor­mal ga­lax­ies, but on smaller scales, and less straight­for­ward sorts of alignments. As­tro­no­mers at­trib­ute the alignments to the ways that ga­lax­ies build them­selves in the first place by ac­cu­mu­lating smaller ob­jects.

In the new stu­dy, re­search­ers us­ing the Eu­ro­pe­an South­ern Ob­ser­va­to­ry’s Very Large Tel­e­scope in Chil­e stud­ied qua­sars, ga­lax­ies with ex­tremely bright cen­ters due to the pres­ence of black holes vo­ra­ciously gob­bling up near­by ob­jects. 

A black hole is an ob­ject so com­pact that its gra­vity sucks in an­y­thing that strays too close, in­clud­ing light. Many ga­lax­ies are be­lieved to con­tain a gi­ant black hole at the cen­ter. A black hole it­self is in­vis­i­ble, but its feed­ing ac­ti­vi­ties cre­ate vi­o­lent dis­tor­tions of near­by ma­te­ri­al that cause it to heat up and give off light. Quasars can shine more brightly than all the stars in the rest of their host ga­lax­ies put to­geth­er.

Quasars are sur­rounded with spin­ning discs of ex­tremely hot ma­te­ri­al, some of which of­ten spouts away in long jets along their ax­es of rota­t­ion. 

A team led by Da­mien Hut­semék­ers from the Uni­vers­ity of Liège in Bel­gium used an in­stru­ment on the tel­e­scope called FORS to study 93 qua­sars that were known to form huge group­ings spread over bil­lions of light-years. The ga­lax­ies are so far away that they are seen as they ex­isted when the Uni­verse was about one third of its cur­rent age. That’s be­cause light takes time to get he­re.

“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 find­ings also suggest that the qua­sar spins tend to fol­low the large-scale struc­tures they in­hab­it. 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 per­cent.

Com­put­er sim­ula­t­ions of the uni­verse had re­vealed si­m­i­lar alignments, but on smaller scales, said study col­la­bo­ra­tor Dom­i­nique Sluse of the Arge­lander Insti­tute for Astron­omy in Bonn, Ger­ma­ny and Uni­vers­ity of Liège. The dis­crep­an­cy “may be a hint that there is a mis­sing in­gre­di­ent in our cur­rent mod­els of the cos­mos,” he added.

The team could­n’t see the spin ax­es or the jets of the qua­sars di­rect­ly. In­stead they meas­ured the “po­lar­iz­a­tion” of each qua­sar’s light. Light is “po­larized” when its waves os­cil­late in the same di­rec­tion. For 19 qua­sars, the re­search­ers found sig­nif­i­cant po­lar­iz­a­tion. They used this along with oth­er in­forma­t­ion to de­duce the an­gle of the disc of ma­te­ri­al fall­ing in­to the black hole, and in turn the spin ax­is of the qua­sar it­self.

Why the alignments at all? Most ob­jects in space, in­clud­ing ga­lax­ies, tend to spin be­cause they form by ac­cu­mu­lating, through gra­vity, smaller ob­jects. These are usu­ally mov­ing with re­spect to each oth­er. These mo­tions af­fect the fi­nal, merged ob­ject by mak­ing it spin, and it won’t stop un­less some­thing spe­cifi­cally stops it.

As­tro­no­mers be­lieve that the ga­lac­tic alignments oc­cur be­cause of the ways fil­a­ments formed in the first place: they ob­tained their ma­te­ri­al pre­sumably be­cause it flowed to­ward them, not away from them or along them. Some con­sist­en­cy in the di­rec­tion of this flow could be ex­pected to lead to a cor­re­spond­ing con­sist­en­cy in the spins of the var­i­ous ga­lax­ies. 

The spin ax­is will tend to be at right an­gles to the di­rec­tion that ma­te­ri­al is flow­ing to­ward a gal­axy as it builds it­self, ac­cord­ing to writ­ings by Elmo Tem­pel of the Tar­tu Ob­serv­a­to­ry in Tora­vere, Es­to­nia, and Noam Libe­skind of the Leib­niz In­sti­tute for As­t­ro­phys­ics in Pots­dam, Ger­ma­ny, who have con­ducted ear­li­er stud­ies on ga­lac­tic alignment.

The new study was pub­lished on Nov. 19 in the jour­nal As­tronomy and As­t­ro­phys­ics.


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New observations suggest that galaxies align with each other across vast reaches of space—in a manner that astronomers had expected, but more so, a report said. The work indicates that over distances of billions of light-years, certain types of super-bright galaxies tend to spin along the same axis. A light-year is the distance light travels in a year. Astronomers attribute the alignments to characteristics of the large-scale “cosmic web,” in which galaxies overall tend to group themselves into a structure that resembles a kind of web stretching out in all directions. A closer look at this web reveals countless galaxies arranged along structures that can be described as filaments, sheets and clumps. The direction of the galaxy’s spin axis, according to the new findings, often follows a filament. Previous studies had detected similar sorts of alignments for normal galaxies, but on smaller scales, and less straightforward sorts of alignments. Astronomers attribute the alignments to the ways that galaxies build themselves in the first place by accumulating smaller objects. In the new study, researchers using the European Southern Observatory’s Very Large Telescope in Chile studied quasars, galaxies with extremely bright centers due to the presence of black holes voraciously gobbling up nearby objects. A black hole is an object so compact that its gravity sucks in anything that strays too close, including light. Most galaxies are believed to contain a giant black hole at the center. A black hole itself is invisible, but its feeding activities create violent distortions of nearby material that cause it to heat up and give off light. Quasars can shine more brightly than all the stars in the rest of their host galaxies put together. Quasars are surrounded with spinning discs of extremely hot material, some of which often spouts away in long jets along their axes of rotation. A team led by Damien Hutsemékers from the University of Liège in Belgium used an instrument on the telescope called FORS to study 93 quasars that were known to form huge groupings spread over billions of light-years. The galaxies are so far away that they are seen as they existed when the Universe was about one third of its current age. That’s because light takes time to get here. “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 also related to the cosmic web. Galaxies aren’t evenly distributed. On scales of billions of light-years they are found to form a giant web of filaments and clumps around huge voids where galaxies are scarce. The new findings indicate that the quasar spins tend to follow the large-scale structures they inhabit. 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 percent. Computer simulations of the universe had revealed similar alignments, but on smaller scales, said study collaborator Dominique Sluse of the Argelander-Institut für Astronomie in Bonn, Germany and University of Liège. The discrepancy “may be a hint that there is a missing ingredient in our current models of the cosmos,” he added. The team couldn’t see the spin axes or the jets of the quasars directly. Instead they measured the “polarization” of each quasar’s light. Light is “polarized” when its waves oscillate in the same direction. For 19 quasars, the researchers found significant polarization. They used this along with other information to deduce the angle of the disc of material falling into the black hole, and in turn the spin axis of the quasar itself. Why the alignments at all? Most objects in space, including galaxies, tend to spin because they form by accumulating, through gravity, smaller objects. These are usually moving with respect to each other. These motions affect the final, merged object by making it spin. Astronomers believe that the galactic alignments occur because of the ways filaments formed in the first place: they obtained their material presumably because it flowed toward them, not away from them or along them. Some consistency in the direction of this flow could be expected to lead to a corresponding consistency in the spins of the various galaxies. The spin axis will tend to be at right angles to the direction that material is flowing toward a galaxy as it builds itself, according to writings by Elmo Tempel of the Tartu Observatory in Toravere, Estonia, and Noam Libeskind of the Leibniz Institute for Astrophysics in Potsdam, Germany, who have conducted earlier studies on galactic alignment. The new study was published on Nov. 19 in the journal Astronomy and Astrophysics.