As­tronomers de­tect the first stars born af­ter the Big Bang

Re­searchers dis­cover an an­cient sig­nal that helps pin­point the mo­ment stars lit up the uni­verse for the first time

All About Space - - Launch Pad -

As­tronomers peer­ing back in time have de­tected a faint ra­dio sig­nal from the very first stars, fi­nally an­swer­ing the ques­tion of when such ce­les­tial bod­ies burst into life. It would ap­pear that the ear­li­est stars be­gan turn­ing on their light some 180 mil­lion years af­ter the Big Bang. If the find­ings re­gard­ing the tim­ing of the so-called Cos­mic Dawn are con­firmed then it will have huge im­pli­ca­tions for our sci­en­tific un­der­stand­ing of the cos­mos.

Sci­en­tists have long known that in the im­me­di­ate af­ter­math of the Big Bang, the uni­verse was cold, dark and fea­ture­less. It was filled with hy­dro­gen and helium and there was much back­ground ra­di­a­tion, known as Cos­mic Mi­crowave Back­ground. But the ques­tion of how and when the uni­verse tran­si­tioned from dark­ness to light has long trou­bled the best of minds. This is why a team led by Judd Bow­man of Ari­zona State Univer­sity sought to de­tect the ear­li­est stars.

They based their work on the the­ory that grav­ity caused the dens­est re­gions of hy­dro­gen gas to co­a­lesce and form com­pact clouds in the wake of the uni­verse's birth. Some of these even­tu­ally col­lapsed in­wards, form­ing mas­sive, blue, yet short-lived stars and, as they emit­ted their ul­tra­vi­o­let light into the dark ar­eas that lay be­tween them, the en­ergy sig­na­ture of the hy­dro­gen atoms changed.

The atoms be­gan to ab­sorb ra­di­a­tion from the Cos­mic Mi­crowave Back­ground at a fre­quency of 1.4 gi­ga­hertz, leav­ing an in­deli­ble mark. Un­der­stand­ing this led to a long-held idea that the ab­sorp­tion should be de­tectable – that it was pos­si­ble to look for a dip in bright­ness of the back­ground ra­di­a­tion. The prob­lem is the ra­dio waves have stretched be­cause they have trav­elled for so long. Other sig­nals also in­ter­fere.

Find­ing the right one was no mean feat, but Dr Bow­man and his team made a break­through af­ter 12 years of ex­per­i­men­tal ef­fort. They used a ta­ble-sized ground-based ra­dio spec­trom­e­ter: Ex­per­i­ment to De­tect the Global EoR Sig­na­ture (EDGES). Based at the Murchi­son Ra­dio-as­tron­omy Ob­ser­va­tory in Western Aus­tralia, where interference is low, the team says it was able to mea­sure the av­er­age ra­dio spec­trum of all of the as­tro­nom­i­cal sig­nals re­ceived across much of the South­ern Hemi­sphere sky.

The eureka mo­ment came af­ter the team ex­tended their search to lower fre­quen­cies in

2015. The in­stru­ment was then able to de­tect a tiny 0.1 per cent dip in the wave­length. “We see this dip most strongly at about 78 mega­hertz,” af­firms Alan Rogers, co-au­thor of the study. “And that fre­quency cor­re­sponds to roughly 180 mil­lion years af­ter the Big Bang. In terms of a di­rect de­tec­tion of a sig­nal from the hy­dro­gen gas it­self, this has got to be the ear­li­est.” If true – and the team spent two years check­ing that the find­ing was not caused by in­stru­men­tal ef­fect and noise – it means those early stars formed a stag­ger­ing 13.6-bil­lion-years ago.

Yet that is not the end of the team's find­ings. Since the size of the dip was twice as large as ex­pected, the study also dis­cov­ered that the uni­verse prior to the for­ma­tion of the first stars was far colder than as­tronomers had orig­i­nally be­lieved. It points to the uni­verse at that stage be­ing -270° Cel­sius (-454° Fahren­heit) – less than half the ex­pected tem­per­a­ture. Ren­nan Barkana of Tel Aviv Univer­sity says this points to the first ev­i­dence that dark mat­ter, which he says is com­posed of low-mass par­ti­cles, si­phoned off en­ergy from nor­mal mat­ter in the early uni­verse. It means the hy­dro­gen gas was los­ing heat to dark mat­ter. “The first stars in the uni­verse turned on the ra­dio sig­nal, while the dark mat­ter col­lided with the or­di­nary mat­ter and cooled it down,” Pro­fes­sor Barkana says.

This makes the dis­cov­ery of the first stars even more im­por­tant than ini­tially imag­ined. “If Barkana’s idea is con­firmed, then we've learned some­thing new and fun­da­men­tal about the mys­te­ri­ous dark mat­ter that makes up 85 per cent of the mat­ter in the uni­verse, pro­vid­ing the first glimpse of physics be­yond the stan­dard model,” said Dr Bow­man. In­deed, be­cause it sug­gests that dark mat­ter is in­ter­act­ing with hy­dro­gen, it turns the the­ory that dark mat­ter is made up of weakly in­ter­act­ing mas­sive par­ti­cles on its head.

As such, Dr Bow­man is not about to stop there. “Now that we know this sig­nal ex­ists, we need to rapidly bring on­line new ra­dio tele­scopes that will be able to mine the sig­nal much more deeply,” he ex­plains, re­fer­ring to in­stru­ments such as the Hy­dro­gen Epoch of Reion­iza­tion Ar­ray (HERA) and the Owens Val­ley Long Wave­length Ar­ray (OVRO-LWA). The next step is to im­prove the per­for­mance of the in­stru­ments to learn more about those early stars. It is also cru­cial that the find­ings are in­de­pen­dently con­firmed.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.