We’re all made of star­dust… from a galaxy far, far away

China Daily (Hong Kong) - - SCIENCE - By SARAH KNAPTON

The idea of find­ing ex­trater­res­trial life on an­other planet, in a dis­tant solar sys­tem or in a far away galaxy has long cap­tured the imag­i­na­tion of humans.

But now sci­en­tists have dis­cov­ered that we are all ac­tu­ally par­tal­ien.

Ac­cord­ing to US as­tro­physi­cists up to half of all mat­ter in our Milky Way galaxy comes from dis­tant ar­eas in space, driven here on strong in­ter­stel­lar winds, cre­ated when stars ex­plode in spec­tac­u­lar su­per­novae.

When Carl Sa­gan, the late Amer­i­can as­tro­physi­cist, made his well­known com­ment that ‘we are made of star-stuff’ he meant that all the el­e­ments on Earth were once pro­duced in the heart of stars be­fore be­ing flung out into the uni­verse in gi­ant ex­plo­sions.

But it was pre­vi­ously thought that those ex­plo­sions oc­curred within Milky Way. Now sci­en­tists sus­pect each one of us is made, in part, from mat­ter cre­ated when far away suns ex­ploded in dis­tant gal­ax­ies.

“Given how much of the mat­ter out of which we formed may have come from other gal­ax­ies, we could con­sider our­selves space trav­el­ers or ex­tra­galac­tic im­mi­grants,” said Dr Daniel Anglés-Al­cázar, of North­west­ern Univer­sity’s as­tro­physics cen­ter, who led the study.

“It is likely that much of the Milky Way’s mat­ter was in other gal­ax­ies be­fore it was kicked out by a pow­er­ful wind, trav­eled across in­ter­ga­lac­tic space and even­tu­ally found its new home in the Milky Way.

In first-of-its-kind anal­y­sis, sci­en­tists used com­puter sim­u­la­tions to recre­ate 3-D mod­els of gal­ax­ies, fol­low­ing their for­ma­tion from just af­ter the Big Bang to the present day.

The sim­u­la­tions show that su­per­novae ex­plo­sions eject huge amounts of gas from gal­ax­ies, which causes atoms to be trans­ported from one galaxy to an­other via pow­er­ful ga­lac­tic winds.

“In our sim­u­la­tions, we were able to trace the ori­gins of stars in Milky Way-like gal­ax­ies and de­ter­mine if the star formed from mat­ter en­demic to the galaxy it­self or if it formed in­stead from gas pre­vi­ously con­tained in an­other galaxy,” added Anglés-Al­cázar, the study’s cor­re­spond­ing au­thor.

Although the atoms travel at great speeds, gal­ax­ies are so far apart from each other, that the the process still takes sev­eral bil­lion years.

But the team found that the trans­fer of mass through ga­lac­tic winds can ac­count for up to 50 per­cent of mat­ter in the larger gal­ax­ies.

“This study trans­forms our un­der­stand­ing of how gal­ax­ies formed from the Big Bang,” said As­sis­tant Pro­fes­sor Claude-An­dré Faucher-Giguère of the Wein­berg Col­lege of Arts and Science, in Illinois.

“What this new mode im­plies is that up to one-half of the atoms around us -- in­clud­ing in the solar sys­tem, on Earth and in each one of us -- comes not from our own galaxy but from other gal­ax­ies, up to one mil­lion light years away.

“Our ori­gins are much less lo­cal than we pre­vi­ously thought. This study gives us a sense of how things around us are con­nected to dis­tant ob­jects in the sky.”

Af­ter the Big Bang 14 bil­lion years ago, the uni­verse was filled with a uni­form gas - no stars, no gal­ax­ies.

But there were tiny per­tur­ba­tions in the gas, and these started to grow by force of grav­ity, even­tu­ally form­ing stars and gal­ax­ies. Af­ter gal­ax­ies formed, each had its own iden­tity, but the new study shows mat­ter moved be­tween them.

The new re­search was pub­lished in the Monthly No­tices of the Royal As­tro­nom­i­cal So­ci­ety.

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