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“Grand” spiral galaxy formed too early, reshuffles standard thinking

July 19, 2012
Courtesy of UCLA
and World Science staff

As­tro­no­mers have iden­ti­fied a ma­jes­tic spir­al gal­axy from very early times—too ear­ly, they say. And it’s reshuf­fling the stand­ard think­ing about how these flor­id struc­tures form.

In find­ings re­ported July 19 in the re­search jour­nal Na­ture, the as­tro­no­mers said they found the gal­axy while us­ing the Hub­ble Space Tel­e­scope to pho­to­graph about 300 very dis­tant ga­lax­ies. 

A com­pos­ite im­age of BX442 from the W.M. Keck Ob­serv­a­to­ry and the Hub­ble Space Tel­e­scope. False col­ors are used to rend­er struc­tures vis­i­ble.

The gal­axy ap­pears ap­prox­i­mately as it looked 10.7 bil­lion years ago, when it gave off the light that we’re only re­ceiv­ing from it now, as­tro­no­mers said. At that time, the uni­verse it­self was only 3 bil­lion years old. Such “grand-de­sign” spir­al ga­lax­ies have nev­er been wit­nessed from such an early time, re­search­ers said.

“As you go back in time to the early uni­verse, ga­lax­ies look really strange, clumpy and ir­reg­u­lar, not sym­met­ric,” said Al­ice Shap­ley of the Uni­vers­ity of Cal­i­for­nia Los An­ge­les, and co-au­thor of the stu­dy. “The vast ma­jor­ity of old ga­lax­ies look like train wrecks. Our first thought was, why is this one so dif­fer­ent, and so beau­ti­ful?”

Ga­lax­ies in to­day’s uni­verse fall in­to var­i­ous types, in­clud­ing spir­al ga­lax­ies like our own Milky Way, which are ro­tat­ing disks of stars and gas in which new stars form, and el­lip­ti­cal ga­lax­ies, which in­clude old­er, red­der stars mov­ing in ran­dom di­rec­tions. The mix of gal­axy struc­tures in the early uni­verse is quite dif­fer­ent, with a much great­er di­vers­ity and larg­er frac­tion of ir­reg­u­lar ga­lax­ies, Shap­ley said.

“The fact that this gal­axy ex­ists is as­tound­ing,” said Da­vid Law of the Uni­vers­ity of To­ron­to, lead au­thor of the stu­dy. “Cur­rent wis­dom holds that such ‘grand-de­sign’ spir­al ga­lax­ies simply did­n’t ex­ist at such an early time in the his­to­ry of the uni­verse.” A ‘grand de­sign’ gal­axy has prom­i­nent, well-formed spir­al arms.

An artist’s ren­der­ing of gal­axy BX442 and its com­pan­ion dwarf gal­axy (up­per left) (Cred­it: Dun­lap In­sti­tute for As­tron­o­my & As­tro­physic­s/Jo Berg­eron)

The gal­axy, which goes by the un­glam­or­ous name BX442, is al­so con­sid­ered large for its ep­och; only about 30 of the ga­lax­ies that Law and Shap­ley an­a­lyzed are as mas­sive as this gal­axy. Law and Shap­ley went to the W.M. Keck Ob­serv­a­to­ry atop Hawai­i’s dor­mant Mauna Kea vol­ca­no and used a light-analyzing in­stru­ment called a spec­tro­graph to con­firm that the ob­ject is a spin­ning spir­al gal­ax­y—and not, for ex­am­ple, two ga­lax­ies that hap­pened to line up in the im­age.

“We first thought this could just be an il­lu­sion,” Shap­ley said. When that doubt was dis­pelled, “We were blown away.”

Exactly how spiral galaxies form in the first place is not well settled.

Why might BX442 look like ga­lax­ies that are so com­mon to­day but were so rare back then? Law and Shap­ley think the an­swer may have to do with a com­pan­ion dwarf gal­axy, which the spec­tro­graph re­veals as a blob at the up­per left of the im­age, and the gravita­t­ional in­ter­ac­tion be­tween the two struc­tures. A sim­ula­t­ion con­ducted by Char­lotte Chris­tensen of the Uni­vers­ity of Ar­i­zo­na, and a co-au­thor of the re­search, backed up that idea.

Even­tu­ally the small gal­axy is likely to merge in­to BX442, Shap­ley said.

“BX442 looks like a near­by gal­axy, but in the early uni­verse, ga­lax­ies were col­lid­ing to­geth­er much more fre­quent­ly,” she said. “Gas was rain­ing in from the in­ter­ga­lac­tic me­di­um [the ar­ea be­tween ga­lax­ies] and feed­ing stars that were be­ing formed at a much more rap­id rate than they are to­day; black holes grew at a much more rap­id rate as well. The uni­verse to­day is bor­ing com­pared to this early time.”

Shap­ley said BX442 rep­re­sents a link be­tween early ga­lax­ies that are much more tur­bu­lent and the ro­tat­ing spir­al ga­lax­ies that we see around us. “In­deed, this gal­axy may high­light the im­por­tance of merg­er in­ter­ac­tions at any cos­mic ep­och in cre­at­ing grand de­sign spir­al struc­ture,” she said.

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Astronomers have identified a majestic spiral galaxy from very early times—too early, they say. And it’s reshuffling the standard thinking about how these florid structures form. In findings reported July 19 in the research journal Nature, the astronomers said they found the galaxy while using the Hubble Space Telescope to photograph about 300 very distant galaxies. The galaxy appears approximately as it looked 10.7 billion years ago, when it gave off the light that we’re only receiving from it now, astronomers said. At that time, the universe itself was only 3 billion years old. Such “grand-design” spiral galaxies have never been witnessed from such an early time, researchers said. “As you go back in time to the early universe, galaxies look really strange, clumpy and irregular, not symmetric,” said Alice Shapley of the University of California Los Angeles, and co-author of the study. “The vast majority of old galaxies look like train wrecks. Our first thought was, why is this one so different, and so beautiful?” Galaxies in today’s universe divide into various types, including spiral galaxies like our own Milky Way, which are rotating disks of stars and gas in which new stars form, and elliptical galaxies, which include older, redder stars moving in random directions. The mix of galaxy structures in the early universe is quite different, with a much greater diversity and larger fraction of irregular galaxies, Shapley said. “The fact that this galaxy exists is astounding,” said David Law of the University of Toronto, lead author of the study. “Current wisdom holds that such ‘grand-design’ spiral galaxies simply didn’t exist at such an early time in the history of the universe.” A ‘grand design’ galaxy has prominent, well-formed spiral arms. The galaxy, which goes by the unglamorous name BX442, is also considered large for its epoch; only about 30 of the galaxies that Law and Shapley analyzed are as massive as this galaxy. Law and Shapley went to the W.M. Keck Observatory atop Hawaii’s dormant Mauna Kea volcano and used a light-analyzing instrument called a spectrograph to confirm that the object is a spinning spiral galaxy—and not, for example, two galaxies that happened to line up in the image. “We first thought this could just be an illusion,” Shapley said. When that doubt was dispelled, “We were blown away.” Why does BX442 look like galaxies that are so common today but were so rare back then? Law and Shapley think the answer may have to do with a companion dwarf galaxy, which the spectrograph reveals as a blob at the upper left of the image, and the gravitational interaction between the two structures. A simulation conducted by Charlotte Christensen of the University of Arizona, and a co-author of the research, backed up that idea. Eventually the small galaxy is likely to merge into BX442, Shapley said. “BX442 looks like a nearby galaxy, but in the early universe, galaxies were colliding together much more frequently,” she said. “Gas was raining in from the intergalactic medium [the area between galaxies] and feeding stars that were being formed at a much more rapid rate than they are today; black holes grew at a much more rapid rate as well. The universe today is boring compared to this early time.” Shapley said BX442 represents a link between early galaxies that are much more turbulent and the rotating spiral galaxies that we see around us. “Indeed, this galaxy may highlight the importance of merger interactions at any cosmic epoch in creating grand design spiral structure,” she said.