The James Webb Space Telescope reveals an exceptionally detailed view of “youth galaxies” 2 to 3 billion years after the Big Bang
Photo: JWST telescope image of a galaxy cluster called “El Gordo,” which is an example of a “cosmic teenager.” Image credit: NASA/ESA/CSA.
According to current calculations, the universe began 13.77 billion years ago with a massive explosion that we know as the Big Bang. Galaxies that formed just two or three billion years after the Big Bang, or shortly after in astronomical terms, are very hot and glow with the light of surprising elements like nickel. The light that reaches us from them now is very faint after billions of years, and that is exactly the specialty of the James Webb Space Telescope (JWST).
These “teenage” galaxies are the subject of new work led by Gwen Rudie of Carnegie and Allison Strom of Northwestern University. Studying juvenile galaxies in the early universe can give scientists insight into how these massive star systems mature and evolve.
Their results, published in The Astrophysical Journal Letters, are part of the CECILIA (Chemical Evolution Constrained using Ionized Lines in Interstellar Aurorae) study developed by Rudie and Strom. Last July, they pointed the JWST at 33 specially selected ancient galaxies whose light traveled more than 10 billion years to reach us and stared for more than a day with the new telescope, providing the most detailed look at these primitive galaxies ever has been recorded so far.
The youthful galaxies of the young universe
During the universe’s youth, many galaxies, including the 33 selected for this study, experienced a period of intense star formation. Today, some galaxies, like our Milky Way, continue to form new stars, although not as quickly. Other galaxies have stopped forming stars altogether. This new work could help astronomers understand the reasons for these different trajectories.
“We are trying to understand how galaxies grew and changed over 14 billion years of cosmic history,” explains lead author Allison Strom. “Through JWST, our program focuses on youthful galaxies who have experienced a difficult period of growth and change. Young people often experience experiences that determine their path into adulthood. The same thing happens with galaxies.
The CECILIA team examined the spectra of these distant galaxies and separated their light into its individual wavelengths, in the same way that a prism distributes sunlight into the colors of the rainbow. Observing light in this way helps astronomers measure the temperature and chemical composition of cosmic sources.
“We averaged the spectra of all 33 galaxies to produce the deepest spectrum ever seen from a distant galaxy, which would require 600 telescopic hours to reproduce,” explains Rudie. “This allowed us to create a kind of atlas that will serve as a basis for future JWST observations of very distant objects.”
Thanks to the spectra, the researchers were able to identify eight different elements: hydrogen, helium, nitrogen, oxygen, silicon, sulfur, argon and nickel.
“The existence of these elements in these galaxies is no surprise, but our ability to measure their light is unprecedented and demonstrates the power of JWST,” Rudie said.
All elements heavier than hydrogen and helium are formed inside stars. When stars explode in violent events like supernovae, they spew these elements into the cosmic environment, where they are integrated into the next generation of stars. By revealing the presence of certain elements in these primitive galaxies, astronomers can learn how star formation changes as they evolve.
Nickel in juvenile galaxies
The CECILIA team was surprised by the presence of nickel, which is particularly difficult to observe. “Never in my wildest dreams did I think we would see nickel,” Strom says. “This is not observed even in nearby galaxies. There must be enough element in a galaxy and the right conditions to be able to observe it. Nobody ever talks about watching nickel. In order for us to see them, the elements in the gas must glow. “For us to see nickel, there could be something unique about stars in galaxies.”
“JWST is still a very new observatory,” adds study co-author Ryan Trainor of Franklin & Marshall College. “Astronomers around the world are still trying to figure out how best to analyze the data we get from the telescope.”
Another surprise: the teenage galaxies were extremely hot. By studying the spectra, physicists can calculate the temperature of a galaxy. While the hottest pockets of galaxies can reach more than 9,700 degrees Celsius or 17,492 degrees Fahrenheit, the juvenile galaxies reached more than 13,350 degrees Celsius or 24,062 degrees Fahrenheit.
“We expected that these early galaxies would have very different chemistry than our Milky Way and the galaxies around us today,” explains Rudie. “But we were still surprised by what the JWST revealed.”
The project was named in honor of Cecilia Payne-Gaposchkin, a pioneer in solar chemistry nearly 100 years ago. His discoveries upended the scientific community’s understanding of the sun’s composition, and he faced years of unfair criticism before his pioneering work was finally recognized.
“With the name Cecilia Payne we would like to honor her groundbreaking studies on the chemical composition of stars. “Allison and I recognize that our own work revealing the chemistry of these very early galaxies builds on his legacy,” explained Rudie.
REFERENCE
CECILIA: The weak emission line spectrum of z ∼ 2–3 star-forming galaxies