Su­per­stars shaped the uni­verse

Many more stars mil­lion times brighter than the Sun over­turn past mod­els.

Cosmos - - Digest -

Our Sun is com­monly held to be an av­er­age sized star. Sadly, it now ap­pears to be a pip­squeak com­pared to the mon­sters that ruled the early cos­mos.

That’s the find­ing of a team of in­ter­na­tional as­tronomers who pointed the Euro­pean South­ern Ob­ser­va­tory’s Very Large Tele­scope in Chile at the Large Mag­el­lanic Cloud, a galaxy about 160,000 light-years away.

The team ex­am­ined about 800 stars in a ‘star­burst’ re­gion called 30 Do­radus or the Taran­tula Ne­bula, and were sur­prised to count dozens of stars 30 to 200 times the mass of the Sun.

Their find­ings, pub­lished in the jour­nal Science, chal­lenge the be­lief that small stars com­prised the vast ma­jor­ity of pri­mor­dial stel­lar mat­ter. If the find­ings from this nearby galaxy hold true for more dis­tant, early gal­ax­ies, it has ma­jor ram­i­fi­ca­tions for un­der­stand­ing the his­tory of the uni­verse.

Af­ter the ini­tial fury of the Big Bang, cos­mol­o­gists be­lieve that the early uni­verse was a cold, dark place pop­u­lated by clouds of neu­tral hy­dro­gen and he­lium. The ‘dark age’ ended a few hun­dred mil­lion years later, as grav­i­ta­tional at­trac­tion be­tween the atoms caused them to slowly clot and form the first stars and gal­ax­ies. As these stars ig­nited, they not only brought light back to the Uni­verse, but show­ered it with ion­iz­ing ra­di­a­tion, stel­lar winds and shock waves from ex­plod­ing su­per­novae. These pressed back against the con­dens­ing gas, putting the brakes on the rate of star for­ma­tion.

This “reg­u­lated” the star-form­ing process so it con­tin­ues to­day, says the study’s lead author, Fabian Sch­nei­der of the Univer­sity of Ox­ford. “Oth­er­wise it would have stopped early on.”

The dis­cov­ery of so many su­per­stars sug­gests that these gi­ants may have played a larger role in this process than pre­vi­ously re­alised. That’s be­cause the im­pact of these mas­sive stars lies not so much in their size but their bright­ness.

A star 100 times the mass of the Sun would be a mil­lion times brighter, Sch­nei­der ex­plains.

Such stars are ‘cos­mic en­gines’, blast­ing out ion­is­ing ra­di­a­tion and strong stel­lar winds. They also die young in mas­sive ex­plo­sions that cre­ate black holes and neu­tron stars, and dis­perse el­e­ments – such as car­bon, oxy­gen, sil­i­con and iron – nec­es­sary to cre­ate plan­ets and life.

The big­gest caveat to the new find is that the Taran­tula Ne­bula may not be typ­i­cal of star-form­ing re­gions in the ear­li­est gal­ax­ies. For one thing, it has too many heav­ier el­e­ments, typ­i­cal of more ma­ture gal­ax­ies.

But if the pre­dic­tions are cor­rect, and su­per­stars were common, that means the uni­verse will also have more black holes than pre­dicted since they are the end stage of mas­sive stars. Ac­cord­ing to Sch­nei­der, the for­ma­tion rate might be 180% higher.

If the new pa­per – “An ex­cess of mas­sive stars in the lo­cal 30 Do­radus star­burst” – is cor­rect, we should de­tect more grav­i­ta­tional waves from black hole merg­ers, says Brad Tucker, an as­tro­physi­cist and cos­mol­o­gist at Aus­tralian Na­tional Univer­sity: “Sim­ply put, more larger stars equals a more ex­cit­ing uni­verse.”

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