“Cosmic Dawn” of our Universe ended much later than we thought

(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 at dawn, which determined the shape of the nascent cosmos.

Having a timeline for this colossal shift would go a long way in helping 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 has used light from a dozen distant objects called quasars to remove uncertainty, determining that the last large wisps of hydrogen “fog” burned up much later than we first thought, more than a billion years later. after the Big Bang.

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

As the temperature dropped, hydrogen atoms formed, simple structures made up of single protons combined with single electrons.

Soon the entire universe was filled with an unchar of atoms, their sea swaying back and forth in the endless darkness.

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

That first sunrise—the beginning of the cosmic dawn—drenched the surrounding hydrogen haze 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 rays of these early stars to the re-ionization of the last remaining pockets of primordial hydrogen, has never been clear.

Research more than 50 years ago used the way in which light from highly active galactic nuclei (called quasars) was absorbed by intermediate gas floating in the nearby intergalactic medium. Find a series of quasars receding into the distance and you can effectively see the ionization timeline of neutral hydrogen gas.

Knowing the theory is one thing. From a practical standpoint, it is difficult to interpret an accurate time scale from 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 ripple of ionized hydrogen across the sky, the researchers expanded their sample by tripling the previous amount of high-quality spectral data, analyzing the light from a total of 67 quasars.

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

According to their own data, the last remnants of primordial hydrogen were exposed to 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,” says astronomer Frederick Davies of the Max Planck Astronomical Institute in Germany.

“Now we have the strongest evidence that this process ended much later, in the space age, which is easier to observe with the current generation of observational tools.”

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

“This new data set provides a crucial benchmark against which numerical simulations of the first billion years of the universe will be tested for years to come,” says Davis.


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