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 Large Bang, the cosmos was a really darkish place. The glow of the universe’s explosive beginning had cooled, and space was stuffed with dense fuel —largely hydrogen—with no sources of sunshine.

Slowly, over tons of of tens of millions of years, the fuel was drawn into clumps by gravity, and ultimately, the clumps grew sufficiently big to ignite. These had been the first stars.

At first their mild did not journey far, as a lot of it was absorbed by a fog of hydrogen fuel. Nonetheless, as increasingly stars shaped, they produced sufficient mild to burn away the fog by “reionizing” the fuel—creating the clear universe dotted with sensible 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 research published in Nature, we used a huge cluster of galaxies as a magnifying glass to stare upon faint relics of this time—and found that stars in small, faint dwarf galaxies had been seemingly liable for this cosmic-scale transformation.

What ended the darkish ages?

Most astronomers already agreed that galaxies had been the principle power in reionizing the universe, however it wasn’t clear how they did it. We all know that stars in galaxies ought to make loads of ionizing photons, however these photons want to flee the dust and fuel inside their very own galaxy to ionize hydrogen out within the space 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 massive black holes could have been accountable.)

There are two camps amongst adherents of the galaxy concept.

The primary thinks big, huge galaxies produced the ionizing photons. There weren’t many of those galaxies within the early universe, however each produced loads of mild. So if a sure fraction of that mild 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 large variety of a lot smaller galaxies within the early universe. Every one in all these would have produced far much less ionizing mild, however with the load of their numbers, they might have pushed the epoch of reionization.

A magnifying glass 4 million lightyears large

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

We needed a have a look at a few of the faintest galaxies round, so we used an enormous group of galaxies known as Pandora’s Cluster as a magnifying glass. The big mass of the cluster distorts space and time, amplifying the sunshine from objects behind it.

As a part of the UNCOVER program, we used the James Webb Area Telescope to take 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 pricey, so we may solely have a look at eight galaxies in better element.)

The brilliant glow of hydrogen

We chosen some sources which had been round 0.5% of the brightness of our Milky Way galaxy at the moment, and checked them for the telltale glow of ionized hydrogen. These galaxies are so faint they had been solely seen in any respect due to 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 occasions as a lot ionizing mild as we’d contemplate “regular”. That is on the highest finish of what we had predicted, based mostly on our understanding of how early stars shaped.

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

Beforehand, we had thought that round 20% of all ionizing photons would want to flee from these smaller galaxies in the event that they had been to be the dominant contributor to reionization. Our new knowledge suggests even 5% could be adequate—which is in regards to 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 research was solely based mostly on eight galaxies, all near a single line of sight. To verify our outcomes, we might want to have a look at completely different elements of the sky.

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

This text is republished from The Conversation beneath a Artistic Commons license. Learn the original article.