"Long before it's in the papers"
September 11, 2007

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Giant galaxy pileup seen

Aug. 7, 2007
Courtesy NASA
and World Science staff

Four ga­lax­ies are slam­ming in­to each oth­er and kick­ing up bil­lions of stars in one of the larg­est cos­mic smash-ups ev­er ob­served, as­tro­no­mers say.

Spot­ted by NASA’s Spitzer Space Tel­e­scope, the ga­lax­ies will even­tu­ally merge in­to one be­he­moth gal­axy up to 10 times as mas­sive as our own Milky Way, ac­cord­ing to the re­search­ers. They call it a rare sight­ing that of­fers an un­prec­e­dent­ed look at how the big­gest ga­lax­ies form. 

The four yel­low blobs in the mid­dle are large ga­lax­ies that have be­gun to tan­gle and ul­ti­mate­ly merge in­to a sin­gle gar­gan­tu­an gal­axy. (Cre­d­it: NA­SA/JPL-Cal­tech/CXO/WIYN/Har­vard-Smith­son­ian CfA)
“Most of the gal­axy merg­ers we al­ready knew about are like com­pact cars crash­ing to­geth­er,” said Ken­neth Rines of the Har­vard-Smith­son­ian Cen­ter for As­t­ro­phys­ics in Cam­bridge, Mass. “What we have here is like four sand trucks smash­ing to­geth­er, fling­ing sand ev­erywhe­re.” 

Rines is lead au­thor of a pa­per on the find­ings, to ap­pear in the re­search pub­li­ca­tion As­t­ro­phys­i­cal Jour­nal Let­ters.

Col­li­sions, or merg­ers, be­tween ga­lax­ies are com­mon. Gra­vity causes some ga­lax­ies that are close to­geth­er to tan­gle and ul­ti­mately un­ite over pe­ri­ods of mil­lions of years. Though stars in merg­ing ga­lax­ies are tossed around like sand, they have a lot of space be­tween them and sur­vive the ride. 

Our Milky Way gal­axy will team up with the An­drom­e­da gal­axy in five bil­lion years; some cal­cula­t­ions even sug­gest we may end up liv­ing in An­drom­e­da dur­ing part of the pro­cess. 

Merg­ers be­tween one big gal­axy and sev­eral small ones, called mi­nor merg­ers, are well doc­u­mented. For ex­am­ple, one of the most elab­o­rate known mi­nor merg­ers is tak­ing place in the Spi­der­web gal­axy, a mas­sive gal­axy that is catch­ing doz­ens of small ones in its “web” of gra­vity. As­tro­no­mers have al­so wit­nessed “ma­jor” merg­ers among pairs of ga­lax­ies that are si­m­i­lar in size. But no ma­jor merg­ers be­tween mul­ti­ple hefty ga­lax­ies – the big rigs of the gal­axy world – have been seen un­til now, Rines and col­leagues said.

The new quad­ru­ple merg­er was disco­vered by chance dur­ing a Spitzer sur­vey of a dis­tant clus­ter of ga­lax­ies, called CL0958+4702, lo­cat­ed nearly five bil­lion light-years away. A light-year is the dis­tance light trav­els in a year. The tel­e­scope first spot­ted an un­usu­ally large fan-shaped plume of light com­ing out of a gath­er­ing of four blob-shaped, or el­lip­ti­cal, ga­lax­ies. Three of the ga­lax­ies are about the size of the Milky Way, while the fourth is three times as big.

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Four galaxies are slamming into each other and kicking up billions of stars in one of the largest cosmic smash-ups ever observed, astronomers say. Spotted by NASA’s Spitzer Space Telescope, the galaxies will eventually merge into one behemoth galaxy up to 10 times as massive as our own Milky Way, according to the researchers. They call it a rare sighting that offers an unprecedented look at how the biggest galaxies form. “Most of the galaxy mergers we already knew about are like compact cars crashing together,” said Kenneth Rines of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. “What we have here is like four sand trucks smashing together, flinging sand everywhere.” Rines is lead author of a paper on the findings accepted for publication in Astrophysical Journal Letters. Collisions, or mergers, between galaxies are common. Gravity causes some galaxies that are close together to tangle and ultimately unite over periods of millions of years. Though stars in merging galaxies are tossed around like sand, they have a lot of space between them and survive the ride. Our Milky Way galaxy will team up with the Andromeda galaxy in five billion years; some calculations even suggest we may end up living in Andromeda during part of the process. Mergers between one big galaxy and several small ones, called minor mergers, are well documented. For example, one of the most elaborate known minor mergers is taking place in the Spiderweb galaxy—a massive galaxy that is catching dozens of small ones in its “web” of gravity. Astronomers have also witnessed “major” mergers among pairs of galaxies that are similar in size. But no major mergers between multiple hefty galaxies – the big rigs of the galaxy world – have been seen until now, Rines and colleagues said. The new quadruple merger was discovered by chance during a Spitzer survey of a distant cluster of galaxies, called CL0958+4702, located nearly five billion light-years away. A light-year is the distnce light travels in a year. The telescope first spotted an unusually large fan-shaped plume of light coming out of a gathering of four blob-shaped, or elliptical, galaxies. Three of the galaxies are about the size of the Milky Way, while the fourth is three times as big.