Unifying principle said to govern all galaxies
Mar 16,2007 00:00 by Bend_Weekly_News_Sources

As­tro­no­mers have found a math­e­mat­i­cal prin­ci­ple that they say sur­pris­ing­ly fits all gal­ax­ies, from the state­ly spi­ral-shaped ones to the messy “train wrecks.” This could re­veal some­thing deep about the evo­lu­tion of the un­i­verse, they claim.

In a new study us­ing the W.M. Keck Ob­serv­a­to­ry in Ha­waii, the sci­en­tists found that this com­mon­al­i­ty has linked all galax­ies for eight bil­lion years, near­ly half the age of the Uni­verse.

An im­age of col­lid­ing galax­ies cap­tured in 1999 us­ing the Hub­ble Space Tel­e­scope. The ob­jects are part of a large gal­axy clus­ter des­ig­nat­ed MS1054-03. It is about eight bil­lion light-years away, hence shows it­self to us as it looked that num­ber of years ago. (Cour­te­sy Pie­ter van Dokkum, Mar­ijn Franx [U­ni­ver­si­ty of Gronin­gen/Lei­den], ESA and NASA)

All galax­ies, they said, fol­low a con­sist­ent re­la­tion­ship be­t­ween their mass, or weight, and the ve­loc­i­ties of the stars and gas clouds that com­pose them. “We were tru­ly sur­prised at how well” the pat­tern fits a diz­zy­ing ar­ray of ga­l­axy types, said San­d­ra Fa­ber of the Uni­ver­si­ty of Ca­l­i­for­nia, San­ta Cruz, co-au­thor of the stu­dy. 

The re­port is to ap­pear in a forth­com­ing spe­cial is­sue of the re­search pub­li­ca­tion As­t­ro­phys­i­cal Jour­nal Let­ters.

Galax­ies fall in­to three bas­ic types: spi­r­al or disk-like ones such as our own Milky Way; those shaped like round­ish clouds, known as el­lip­ti­cal ga­l­ax­ies; and messy, bashed-up or odd­ball ga­l­ax­ies. These are usu­al­ly thought to be rem­nants of gal­axy col­li­sions, and some­times dubbed “train wrecks.”

Astronomers noted years ago that for spi­r­als and el­lip­ti­cals, there were spe­ci­fic re­la­tion­ships be­t­ween their masses and the ve­loc­i­ties of their con­s­tit­u­ent stars. These rules are called the Tul­ly-Fish­er and the Fa­ber-Jack­son re­la­tions, re­spec­tive­ly.

What was­n’t known, Fa­ber and col­leagues said, was that these two re­la­tion­ships—which seem­ing­ly work dif­ferent­ly—are them­selves re­la­ted, as as­pects of one over­ar­ch­ing rule. And this prin­ci­ple al­so ap­plies to the “train wrecks,” not pre­vi­ously known to re­spect any such law.

Ac­cord­ing to Faber’s group, in all galax­ies, there is some or­der­ly, reg­u­lar ro­ta­tion: the con­stit­u­ent stars and gas clouds re­volve to­geth­er about a com­mon cen­ter. For train-wreck galax­ies, this neat ro­ta­tion is over­laid with a cer­tain amount of mixed-up ve­loc­i­ties.

The re­search­ers de­vised a new meas­ure of the com­po­nents’ to­tal ve­loc­i­ty, which they called a “speed in­di­ca­tor.” It com­bines both the or­der­ly ro­ta­tion ve­loc­i­ty and the ran­dom or dis­or­dered mo­tion. This property turns out to be strict­ly re­lat­ed to the mass of gal­ac­tic com­p­o­nents, said Su­san Kassin, a post­doc­tor­al re­searcher at the uni­ver­si­ty and the stu­dy’s lead au­thor. “Sur­pris­ingly, if you use this new speed in­di­ca­tor to meas­ure the mo­tions of stars and gas in a gal­axy, you can pre­dict the mass in stars the gal­axy has with pret­ty high ac­cu­ra­cy.”

Galax­ies like our Milky Way con­sist of bil­lions of stars formed in­to a spir­al disk along with some gas. Our gal­axy al­so spins like a pin­wheel at a few hun­dred kilo­me­ters (miles) per sec­ond. 

Such el­e­gant galax­ies were scarce once, the sci­en­tists said. As­tro­no­mers can ob­serve the an­cient uni­verse by look­ing ex­treme­ly far away, be­cause this means the light we see left those ar­eas bil­lions of years ago. Half of the age of the uni­verse ago, many galax­ies look more di­shev­eled, as they were be­ing as­sem­bled through gal­axy col­li­sions and the pil­ing on of new gas and stars, Kass­in’s team said.

The new findings in essence show that the mixed-up and or­der­ly ve­loc­i­ties are some­how re­lated, said Ben Weiner of the Uni­ver­si­ty of Ar­i­zo­na in Tuc­son, Ariz., an­oth­er co-au­thor of the stu­dy. “The mixed-up ve­loc­i­ties may set­tle down to or­der­ly ro­ta­tion over time as the uni­verse ages,” he pro­posed.

The find­ings prob­a­bly re­flect an even deepe­r prope­rty of the cos­mos, said Faber, one of the name­sakes of the Faber-Jackson re­la­tion, which she helped de­vel­op in 1976. “Both of these re­la­tions were im­printed by the na­ture of fluc­tu­a­tions [in the uni­verse] that made galax­ies in the first place,” she said. 

“This re­la­tion holds for all the galax­ies, no mat­ter what they look like,” Kassin re­marked. “It ties to­geth­er the Faber-Jackson re­la­tion with the Tully-Fisher re­la­tion and works for all kinds of odd­ball galax­ies that are more com­mon in the ear­ly uni­verse.” The study in­volved 544 far-off galax­ies of var­i­ous types. Kassin said that makes it the larg­est study to date of the speed and move­ment of dis­tant galax­ies’ stars and oth­er mat­ter.

Courtesy World Science