Like cosmic toddlers, galaxies in the young universe were messy and had difficulty settling down, a new study shows.
Using the powerful James Webb Space Telescope (JWST), scientists peered at more than 250 galaxies in the early universe. The research team charted the movement of gas long ago, when the universe was growing up — between 800 million and 1.5 billion years after the Big Bang. (The cosmos is roughly 13.8 billion years old.)
“The bulk of the galaxy population is undergoing a turbulent phase of its evolutionary history,” lead author Lola Danhaive, a doctoral candidate at the University of Cambridge’s Kavli Institute for Cosmology, told Live Science in an email.
Unlike in past studies, Danhaive explained, the team targeted less-massive galaxies and uncovered what they called “messy kinematics,” meaning the galaxies the researchers studied are not stable, rotating disks like the Milky Way and its neighbors.
Turbulence during earlier phases of the universe’s history was much higher than scientists previously thought, Danhaive added, because earlier studies were biased toward larger and more ordered galaxies, which are easier to spot in telescopes than the smaller galaxies targeted in the new study.
“We find evidence that this turbulence in the [galaxy] disk is caused by high amounts of gas, which fuels intense star formation and drives gravitational instabilities,” Danhaive said.
Moreover, the researchers charted how galaxies changed from these chaotic structures into the more regular patterns seen in mature galaxies, providing an unprecedented view of how galaxies grew from youth to maturity.
“At early times, galaxies are undergoing a turbulent phase of assembly, where strong bursts of star formation and high amounts of gas disrupt the ordered motions of the gas disk,” Danhaive said. “At later times, galaxies grow their mass and become more stable.”
Structures like the Milky Way formed more recently, in the past few billion years, as the available gas was taken up by stars and diminished in the galaxy overall. Less free-floating gas allows mature galaxies to grow and change more smoothly than in youthful times.
The study would not have been possible without the JWST, which is perched in a distant, gravitationally stable spot in space far from the stray light of Earth and the moon. The infrared telescope can peer deeper into space than any of its predecessors, and routinely discovers galaxies considered to be the earliest in the known universe. Danhaive said the observatory, paired with simulations, is helping researchers better understand “bursty” star formation and how gas influences a galaxy’s disk.
“Overall, our work opens a window into the dynamics of early galaxy formation,” she said. Next up, the team plans to study the inflows and outflows of gas in individual galaxies by tracing how gas was chemically enriched.
The researchers expect that inflowing gas will be less enriched, or “pristine,” while outflowing gas will have more chemical components, thanks to contributions from individual stars within the galaxy. Examining how gas flows throughout the galaxy may allow researchers to see why some galaxies rotate faster than others, for example.
“There is so much more to uncover with JWST’s amazing capabilities, and we look forward to exploring many more aspects of early galaxy formation,” Danhaive said.
