What ended the ‘dark ages’ in the early universe? New Webb data just brought us closer to solving the mystery

About 400,000 years after the Huge Bang, the cosmos was a really darkish place. The glow of the universe’s explosive delivery had cooled, and area was crammed with dense fuel —principally hydrogen—with no sources of sunshine.

Slowly, over a whole lot of hundreds of thousands of years, the fuel was drawn into clumps by gravity, and finally, the clumps grew large enough to ignite. These have been the primary stars.

At first their gentle did not journey far, as a lot of it was absorbed by a fog of hydrogen fuel. Nonetheless, as an increasing number of stars fashioned, they produced sufficient gentle to burn away the fog by “reionizing” the fuel—creating the clear universe dotted with good factors of sunshine we see right this moment.

However precisely which stars produced the sunshine that ended the darkish ages and triggered this so-called “epoch of reionization”? In analysis revealed in Nature, we used a big cluster of galaxies as a magnifying glass to stare upon faint relics of this time—and found that stars in small, faint dwarf galaxies have been doubtless chargeable for this cosmic-scale transformation.

What ended the darkish ages?

Most astronomers already agreed that galaxies have been the principle power in reionizing the universe, but it surely wasn’t clear how they did it. We all know that stars in galaxies ought to make numerous ionizing photons, however these photons want to flee the mud and fuel inside their very own galaxy to ionize hydrogen out within the area between galaxies.

It hasn’t been clear what sort of galaxies would have the ability to produce and emit sufficient photons to get the job executed. (And certainly, there are those that suppose extra unique objects like large black holes might have been accountable.)

There are two camps amongst adherents of the galaxy principle.

The primary thinks big, large galaxies produced the ionizing photons. There weren’t many of those galaxies within the early universe, however each produced numerous gentle. So if a sure fraction of that gentle managed to flee, it may need been sufficient to reionize the universe.

The second camp thinks we’re higher off ignoring the enormous galaxies and focussing on the massive variety of a lot smaller galaxies within the early universe. Every one in all these would have produced far much less ionizing gentle, however with the burden of their numbers, they might have pushed the epoch of reionization.

A magnifying glass 4 million lightyears large

Attempting to have a look at something within the early universe may be very onerous. The huge galaxies are uncommon, so they’re onerous to seek out. Smaller galaxies are extra widespread, however they’re very faint, which makes it tough (and costly) to get high-quality information.

We wished a take a look at a number of the faintest galaxies round, so we used an enormous group of galaxies referred to as Pandora’s Cluster as a magnifying glass. The big mass of the cluster distorts area and time, amplifying the sunshine from objects behind it.

As a part of the UNCOVER program, we used the James Webb Area Telescope to have a look at magnified infrared pictures of faint galaxies behind Pandora’s Cluster.

We first checked out many alternative galaxies, then selected a number of notably distant (and subsequently historic) ones to look at extra carefully. (This type of shut examination is dear, so we may solely take a look at eight galaxies in better element.)

The intense glow of hydrogen

We chosen some sources which have been round 0.5% of the brightness of our Milky Method galaxy at the moment, and checked them for the telltale glow of ionized hydrogen. These galaxies are so faint they have been solely seen in any respect because of the magnifying impact of Pandora’s Cluster.

Our observations confirmed that these small galaxies did exist within the very early universe. What’s extra, we confirmed they produced round 4 instances as a lot ionizing gentle as we might take into account “regular”. That is on the highest finish of what we had predicted, primarily based on our understanding of how early stars fashioned.

As a result of these galaxies produced a lot ionizing gentle, solely a small fraction of it could have wanted to flee to reionize the universe.

Beforehand, we had thought that round 20% of all ionizing photons would wish to flee from these smaller galaxies in the event that they have been to be the dominant contributor to reionization. Our new information suggests even 5% could be enough—which is concerning the fraction of ionizing photons we see escaping from fashionable galaxies.

So now we are able to confidently say these smaller galaxies may have performed a really giant position within the epoch of reionization. Nonetheless, our examine was solely primarily based on eight galaxies, all near a single line of sight. To verify our outcomes, we might want to take a look at completely different elements of the sky.

We now have new observations deliberate which is able to goal different giant galaxy clusters elsewhere within the universe to seek out but extra magnified, faint galaxies to check. If all goes nicely, we may have some solutions in a number of years.

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