Half the uni­verse’s lost mat­ter found

Waikato Times - - World -

BRI­TAIN: The amount of ob­serv­able mat­ter in the uni­verse has just dou­bled. And, say as­tronomers, that is quite a re­lief.

By look­ing at the ra­di­a­tion from the early uni­verse it is pos­si­ble to work out how much mat­ter there is and what kind it is. But this has led to an ap­par­ent para­dox: half of the or­di­nary mat­ter that was there at the big bang nearly 14 bil­lion years ago seems to be miss­ing.

Two sep­a­rate teams, in­clud­ing sci­en­tists from Ed­in­burgh Univer­sity, have at last tracked it down. They found that the mat­ter ex­ists in fine ten­drils of gas which form links be­tween the uni­verse’s gal­ax­ies.

This gas is dif­fer­ent from so­called dark mat­ter and dark en­ergy, which we know makes up the vast ma­jor­ity of mass in our uni­verse but is in­vis­i­ble. In­stead, these par­ti­cles are of the same kind that make up all the mat­ter we can see.

As­tronomers had pre­dicted the gas would be there but un­til now no in­stru­ment had been sen­si­tive enough to pick it up.

The lat­est work used a phe­nom­e­non known as the Sun­yaevZel’dovich ef­fect, in which the light left over from the big bang fluc­tu­ates ever so slightly after pass­ing through the hot gas.

It is still im­pos­si­ble to see this ef­fect by look­ing at the gap be­tween any two gal­ax­ies. How­ever, if you com­bine the read­ings from hun­dreds of thou­sands of gal­ax­ies, over­lay­ing them on top of each other, then cu­mu­la­tively it be­comes ap­par­ent.

This is what the re­searchers did, find­ing the fil­a­ments of gas ap­pear­ing as a slight dim­ming caused by the Sun­yaev-Zel’dovich ef­fect.

An­drew Pontzen, a reader in cos­mol­ogy at UCL, who was not in­volved in these stud­ies, said the study was prob­a­bly going to be the first of many us­ing this tech­nique to probe the mys­ter­ies of the cos­mos.

‘‘The dif­fi­culty is it is made out of reg­u­lar par­ti­cles, but be­cause they are very thinly spread they are hard to see,’’ he said.

‘‘This work is a cross-check to see they re­ally are there in the mod­ern uni­verse, and that some­thing hasn’t gone ter­ri­bly wrong. If you didn’t find this you’d be re­ally wor­ried.’’

In par­tic­u­lar, it was com­fort­ing to find out that not only did the mat­ter ex­ist, but that it was broadly where as­tronomers ex­pected it to be.

Pontzen said cos­mol­o­gists now wanted to find things that they did not ex­pect in or­der to solve a far greater mys­tery.

‘‘What this tech­nique is show­ing you is a nor­mal gas that is hard to pick up but is fun­da­men­tally made out of the same stuff you and I are made out of,’’ he said.

‘‘It’s very help­ful to con­firm that this stuff is there, but it isn’t dark mat­ter. We’ve got a much big­ger prob­lem on our hands, which is that 95 per cent of the uni­verse seems to be miss­ing.’’ –

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