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About 400,000 years after the Large Bang, the cosmos was a really darkish place. The glow of the universe’s explosive delivery had cooled, and house was stuffed with dense fuel —largely hydrogen—with no sources of sunshine.
Slowly, over a whole bunch of tens of millions of years, the fuel was drawn into clumps by gravity, and finally, the clumps grew sufficiently big to ignite. These have been the first stars.
At first their gentle did not journey far, as a lot of it was absorbed by a fog of hydrogen fuel. Nevertheless, as increasingly 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 at present.
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 have been seemingly chargeable for this cosmic-scale transformation.
What ended the darkish ages?
Most astronomers already agreed that galaxies have been the principle pressure in reionizing the universe, nevertheless it wasn’t clear how they did it. We all know that stars in galaxies ought to make a whole lot of ionizing photons, however these photons want to flee the mud and fuel inside their very own galaxy to ionize hydrogen out within the house between galaxies.
It hasn’t been clear what sort of galaxies would be capable of produce and emit sufficient photons to get the job finished. (And certainly, there are those that suppose extra unique objects like large black holes could have been accountable.)
There are two camps amongst adherents of the galaxy concept.
The primary thinks large, large galaxies produced the ionizing photons. There weren’t many of those galaxies within the early universe, however each produced a whole lot of gentle. So if a sure fraction of that gentle managed to flee, it might need been sufficient to reionize the universe.
The second camp thinks we’re higher off ignoring the large 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 gentle, however with the load of their numbers, they might have pushed the epoch of reionization.
A magnifying glass 4 million lightyears broad
Making an attempt to take a look at something within the early universe may be very laborious. The huge galaxies are uncommon, so they’re laborious to search out. Smaller galaxies are extra widespread, however they’re very faint, which makes it troublesome (and costly) to get high-quality data.
We wished a take 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 large mass of the cluster distorts house and time, amplifying the sunshine from objects behind it.
As a part of the UNCOVER program, we used the James Webb House Telescope to take a look at magnified infrared photos of faint galaxies behind Pandora’s Cluster.
We first checked out many various galaxies, then selected a couple of notably distant (and due to this fact historic) ones to look at extra intently. (This type of shut examination is dear, so we might solely take a look at eight galaxies in higher element.)
The brilliant glow of hydrogen
We chosen some sources which have been round 0.5% of the brightness of our Milky Means 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 contemplate “regular”. That is on the highest finish of what we had predicted, based mostly 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 will 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 knowledge suggests even 5% can be enough—which is in regards to the fraction of ionizing photons we see escaping from trendy galaxies.
So now we are able to confidently say these smaller galaxies might have performed a really giant position within the epoch of reionization. Nevertheless, our research was solely based mostly on eight galaxies, all near a single line of sight. To substantiate our outcomes, we might want to take a look at totally different elements of the sky.
We’ve got new observations deliberate which can 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 couple of years.
