Using the James Webb Space Telescope, astronomers have discovered that just 500 million years after the Big Bang, galaxies were already pumping heavy elements into their surroundings. That means the early universe wasn't as pure and unspoiled as previously believed, potentially impacting our theories of cosmic evolution.
Soon after the universe began, it was filled with the lightest element, hydrogen, and a little helium. As such, the first stars formed from these elements — but as these stars aged, they forged heavier elements, which astronomers collectively call "metals." These metals were dispersed when these first, or POP III, stars exploded at the end of their lives. This meant the next generations of stars, POP II and POP I, stars were progressively more metal-enriched.
This we all knew, but new James Webb Space Telescope (JWST) research suggests the process occurred earlier than previously thought. What this means is the gas surrounding galaxies was richer in metals like oxygen and carbon when the universe was just 3% of its current age.
"If you start out with pure vanilla ice cream but start mixing in sprinkles soon after, it won't be long until you can no longer find any pristine, plain, vanilla ice cream," team leader Yongda Zhu of the University of Arizona said in a statement. "We observed that heavy elements escaped from galaxies very, very early in cosmic time.
"Not only were the galaxies producing these elements, but they were also dispersing them, possibly seeding other galaxies."
Back to the beginning
To better understand the composition of the early cosmos, Zhu and colleagues used the JWST data to observe three galaxies that are seen as they were around 13.3 billion years ago. This corresponds with an important point in the evolution of the universe called the Epoch of Reionization.
At this time, the light from the first stars was stripping electrons from the hydrogen gas between them, a process called ionization. This allowed light to travel more easily through the cosmos, ending the so-called cosmic dark ages.
"We used the galaxies themselves as background light sources," said Zhu. "As light from the galaxies traveled toward Earth, it passed through surrounding gas, and we were able to look at the light's absorption patterns to detect specific elements."
That's possible because elements absorb and emit light at characteristic wavelengths, meaning when starlight passes through interstellar clouds, the elements within those clouds leave distinct fingerprints in that light.
The observations revealed gas containing oxygen, carbon, silicon and other metals flowing from these early galaxies into intergalactic space.
The chemical fingerprints of this gas more closely resembled those of modern galaxies than was expected. That means early galaxies were already pumping metals into the cosmos.
"Think of these elements, which originated from the galaxies' stars, as food dye dropped into a cup of water," said Zhu. "The color begins to spread through the water, and, in a similar fashion, these heavy elements from early galaxies began to escape into space and 'enrich' their surroundings."
The discovery could explain why astronomers have thus far struggled to find POP III stars. They have been looking for signs of starlight illuminating pristine hydrogen gas, but this gas was gone much earlier than they knew.
The team's research was published on Thursday (Sept. 24) in the journal Nature Astronomy.
