Su­per­novas show the uni­verse ex­pands at the same rate in all di­rec­tions

Sun.Star Pampanga - - SCIENCENEWS! -

An anal­y­sis of ex­plod­ing stars re­veals the uni­verse’s sym­met r y

The cos­mos doesn’t care whether you’re look­ing up or down, left or right: In all di­rec­tions, the uni­verse is ex­pand­ing at the same clip. When com­pared across large swaths of the sky, ex­pan­sion rates agree to bet­ter than 1 per­cent, re­searchers re­port in a pa­per in press in Phys­i­cal Re­view Let­ters.

Ob­ser­va­tions of ex­plod­ing stars, or su­per­novas, in­di­cate that the uni­verse is not only ex­pand­ing, but that ex­pan­sion is ac­cel­er­at­ing over time (SN On­line: 1/16/18).

To check if that ex­pan­sion pro­ceeds apace in dif­fer­ent parts of the sky, the sci­en­tists stud­ied more than 1,000 ex­plod­ing stars called type 1a su­per­novas, which det­o­nate with a known bright­ness. By mea­sur­ing how much the su­per­novas’light is stretched as space ex­pands, re­searchers can es­ti­mate how fast the uni­verse spreads out, and see if the data dif­fer from what would be ex­pected for a uni­form ex­pan­sion.

Even in a per­fectly evenly ex­pand­ing uni­verse, there’s bound to be a bit of noise — a sort of ran­dom jit­ter — in the data. Pre­vi­ous analy­ses have re­lied on com­puter sim­u­la­tions to es­ti­mate the ex­pected noise. But “it’s a real pain to get sim­u­la­tions to have all the right bells and whis­tles” nec­es­sary for fully re­li­able re­sults, says the­o­ret­i­cal cos­mol­o­gist Dra­gan Huterer of the Uni­ver­sity of Michi­gan in Ann Ar­bor. So Huterer and col­leagues in­stead used a scram­bled ver­sion of the su­per­nova data to gauge how much noise to ex­pect, a tech­nique Huterer says is more re­li­able.

The re­sults con­firm cos­mol­o­gists’ un­der­stand­ing of the uni­verse. Ac­cord­ing to the the­ory of in­fla­tion, the uni­verse ex­panded ex­tremely rapidly just after the Big Bang (SN: 7/ 28/ 12, p.20). That ex­pan­sion is thought to have pro­ceeded equally in all di­rec­tions, set­ting up the uni­verse’s uni­form spread­ing to­day.

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