A computer simulation for a paper by Michele Fumagalli and colleagues shows… (Ceverino, Dekel and Primack,…)
For the first time, astronomers have discovered clouds of pristine gas in the distant universe about 12 billion light-years away. The finding offers a peek at what primordial gas looked like just a few minutes after the big bang, before heavier elements formed — a time when star formation was very different than it is today.
The gas clouds, which appear — surprisingly — to have survived for about 2 billion years after the big bang almost 14 billion years ago, were discovered through looking at the light from distant quasars, some of the brightest objects in the universe.
On its way to Earth, light from the quasars passed through gas, which absorbed certain wavelengths. Those missing spots in the light spectrum that reached Earth, called absorption lines, gave scientists an individual fingerprint of the chemicals contained in the gases.
Clouds like these, full of hydrogen and helium, often serve as cradles for star formation as the gases condense. They generally contain heavier elements such as carbon, silicon and oxygen, which are needed for gases to coalesce into the kinds of stars we know today.
But in this case, unlike any cloud scientists had seen before, the clouds contained no absorption lines for these heavier elements, according to a study released this week by the journal Science. This implied that the gas clouds could be very primitive in nature.
In the first few minutes after the big bang, only the lightest elements — mostly hydrogen and helium — were forged. They condensed into the first stars over the next few hundred million years.
The earliest stars "must have looked very different from stars formed today — they would be much bigger and very short-lived," said Robert Simcoe, an astronomer at MIT who was not involved in the study.
"We have not seen those stars, but if they were going to form, this would be the kind of gas from which they'd form."
Over time, these first stars began to form heavier elements through the nuclear fusion powering their cores. When they later exploded, they sent the heavier elements out into the universe, seeding other, younger clouds of gas that condensed into the stars we know today.
Many scientists believed that they had not found any pristine gas clouds left over from those earlier times because the heavier elements from those first stars had been thoroughly dispersed throughout the universe.
"It was surprising to see, after two billion years, the gas was not polluted, left untouched," said lead author Michele Fumagalli, an astronomer at UC Santa Cruz.
The researchers cannot pin down the size of the gas clouds. And they're not sure how common such clouds may be.
But, Fumagalli said, if they are more common than thought, it means the heavy elements didn't disperse as totally or equally as believed; this, in turn, would require a reevaluation of what scientists think they know about how matter flows between galaxies and through the universe.