First “cosmic dawn” lasted much longer than astronomers thought – almost a billion years

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(ORDO NEWS) — For tens of millions of years, our newborn Universe was enveloped in hydrogen. Gradually, this vast fog was torn apart by the light of the very first stars, which determined the shape of the emerging cosmos. But how long did this process actually take?

Having a timeline within this colossal shift would help us understand the evolution of the universe, but so far our best attempts have been fuzzy estimates based on poor quality data.

An international team of astronomers, led by the Max Planck Astronomical Institute in Germany, used light from dozens of distant objects called quasars to resolve uncertainty by determining that the last large wisps of hydrogen “fog” burned up much later than we first thought: more have passed since the Big Bang. billion years.

The first 380,000 years were a static hiss of subatomic particles solidifying in the cooling vacuum of expanding space-time.

As soon as the temperature dropped, hydrogen atoms were formed – simple structures consisting of single protons combined with single electrons. Soon the entire universe was filled with uncharged atoms, a sea of ​​which swayed back and forth in the endless darkness.

Where crowds of neutral hydrogen atoms gathered under the unpredictable push of quantum laws, gravity took over, drawing more and more gas into balls where nuclear fusion could begin.

The first “cosmic dawn” that broke out flooded the surrounding hydrogen fog with radiation, knocking their electrons out of their protons and turning the atoms back into the ions they once were.

How long this “dawn” took, from the first light of those early stars to the reionization of the last remaining pockets of primordial hydrogen, has never been clear.

Research done over 50 years ago used a method of absorbing light from highly active galactic nuclei (called quasars) by intermediate gas floating in the nearby intergalactic medium. Find a series of quasars receding into the distance, you can effectively see the neutral hydrogen gas ionization timeline.

But knowing the theory is one thing. From a practical point of view, it is difficult to interpret the exact time scale for a handful of quasars. Not only is their light distorted by the expansion of the universe, it also passes through pockets of neutral hydrogen formed long before cosmic dawn.

To better understand this stuttering of ionized hydrogen across the sky, the researchers expanded their sample by tripling the previous amount of high-quality spectral data, analyzing a total of light from 67 quasars.

The goal was to better understand the influence of these fresher pockets of hydrogen atoms, allowing researchers to better identify more distant ionization bursts.

It turned out that the last remnants of the original hydrogen fell out under the rays of first-generation starlight about 1.1 billion years after the Big Bang.

“Until a few years ago, the prevailing view was that reionization ended almost 200 million years earlier,” explained astronomer Frederick Davies of the Max Planck Astronomical Institute in Germany.

Future technologies capable of directly detecting the spectral lines emitted by hydrogen reionization should be able to clarify not only when this epoch ended, but also provide important details of how it unfolded.


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