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Mysterious dance of dwarfs may force a cosmic rethink

Mysterious dance of dwarfs may force a cosmic rethink

A find­ing that many small ga­lax­ies don't “swarm” around larg­er ones like bees but rath­er circle them in disc-shaped or­bits is cre­at­ing a new co­nun­drum for sci­en­tists.

Last year “we an­nounced our startling dis­cov­ery that half of the dwarf ga­lax­ies sur­round­ing the An­drom­e­da Gal­axy are or­bit­ing it in an im­mense plane,” said phys­i­cist Ge­raint Lew­is from the Uni­vers­ity of Syd­ney in Aus­tral­ia. “This plane is more than a mil­lion light years in di­am­e­ter, but is very thin, with a width of only 300,000 light years.”

Now, as­tro­no­mers are ex­tend­ing the find­ing to oth­er ga­lax­ies.

The uni­verse con­tains bil­lions of ga­lax­ies. Some, such as the Milky Way, are im­mense, con­tain­ing hun­dreds of bil­lions of stars. Most ga­lax­ies, how­ev­er, are dwarfs, much smaller and with only a few bil­lion stars. For dec­ades as­tro­no­mers have used com­put­er mod­els to pre­dict how these dwarf ga­lax­ies should or­bit large ga­lax­ies. They had al­ways found that they should be scat­tered ran­dom­ly.

“Our An­drom­e­da dis­cov­ery did not agree with ex­pecta­t­ions, and we felt com­pelled to ex­plore if it was true of oth­er ga­lax­ies through­out the uni­verse,” said Lew­is. Us­ing the Sloan Dig­it­al Sky Sur­vey, a re­source of col­or im­ages and 3-D maps cov­er­ing more than a third of the sky, the re­search­ers dis­sect­ed the prop­er­ties of thou­sands of near­by ga­lax­ies.

“We were sur­prised to find that a large pro­por­tion of pairs of sat­el­lite ga­lax­ies have op­po­sitely di­rect­ed ve­lo­ci­ties if they are sit­u­at­ed on op­po­site sides of their gi­ant gal­axy hosts,” said Neil Ibata of the Ly­cée In­terna­t­ional in Stras­bourg, France, lead au­thor of a new study on the find­ings, pub­lished July 20 in the jour­nal Na­ture.

“Ever­ywhere we looked we saw this strangely co­her­ent co­or­di­nated mo­tion of dwarf ga­lax­ies. From this we can ex­trap­o­late that these cir­cu­lar planes of danc­ing dwarfs are uni­ver­sal, seen in about 50 per­cent of ga­lax­ies,” said Lew­is. “This is a big prob­lem that con­tra­dicts our stand­ard cos­mo­lo­g­i­cal mod­els. It chal­lenges our un­der­stand­ing of how the uni­verse works in­clud­ing the na­ture of dark mat­ter,” an un­seen ma­te­ri­al that is de­tected through its gra­vity.

The re­search­ers be­lieve the an­swer may be hid­den in some cur­rently un­known phys­i­cal pro­cess that gov­erns how gas flows in the uni­verse. Some ex­perts have made more rad­i­cal sug­ges­tions, in­clud­ing bend­ing and twist­ing the laws of gra­vity and mo­tion. “Throw­ing out seem­ingly es­tab­lished laws of phys­ics is un­palat­able,” said Pro­fes­sor Lew­is, “but if our ob­serva­t­ions of na­ture are point­ing us in this di­rec­tion, we have to keep an open mind. That's what sci­ence is all about.”

source : http://www.world-science.net

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