NASA’s James Webb Space Telescope (JWST) has identified the earliest-known galaxy, an unexpectedly bright and large formation from the universe’s infancy, only 2% of its current age. This galaxy, named JADES-GS-z14-0, was observed as it existed about 290 million years after the Big Bang, which occurred roughly 13.8 billion years ago. This era is known as the cosmic dawn.
Since becoming operational in 2022, the JWST has transformed our understanding of the early universe. The discovery of JADES-GS-z14-0 was made by the JWST Advanced Deep Extragalactic Survey (JADES) research team.
Measuring about 1,700 light-years across, JADES-GS-z14-0 has a mass equivalent to 500 million stars the size of our sun and was rapidly forming about 20 new stars per year. A light year is the distance light travels in one year, approximately 5.9 trillion miles (9.5 trillion km).
Prior to Webb’s observations, scientists did not know galaxies could exist so early in the universe, especially luminous ones like this.
“The early universe has surprise after surprise for us,” said astrophysicist Kevin Hainline of Steward Observatory at the University of Arizona, a leader of the study. “I think everyone’s jaws dropped,” added astrophysicist and study co-author Francesco D’Eugenio of the Kavli Institute for Cosmology at the University of Cambridge. “Webb is showing that galaxies in the early universe were much more luminous than we had anticipated.”
Previously, the earliest-known galaxy dated to about 320 million years after the Big Bang, announced by the JADES team last year.
“It makes sense to call the galaxy big because it’s significantly larger than other galaxies that the JADES team has measured at these distances, and it’s going to be challenging to understand just how something this large could form in only a few hundred million years,” Hainline said.
“The fact that it’s so bright is also fascinating, given that galaxies tend to grow larger as the universe evolves, implying that it would potentially get significantly brighter in the next many hundred million years,” he added.
Although large for its time, JADES-GS-z14-0 is much smaller than some present-day galaxies. The Milky Way, for instance, is about 100,000 light-years across with a mass equivalent to about 10 billion sun-sized stars.
In the same study, the JADES team announced the discovery of the second-oldest known galaxy, JADES-GS-z14-1, which formed about 303 million years after the Big Bang. This smaller galaxy has a mass equivalent to about 100 million sun-sized stars, measures roughly 1,000 light-years across, and forms about two new stars per year.
“These galaxies formed in an environment that was much more dense and gas-rich than today. Additionally, the chemical composition of the gas was very different, much closer to the pristine composition inherited from the Big Bang—hydrogen, helium, and traces of lithium,” D’Eugenio explained.
Star formation in the early universe was much more violent than today, with massive, hot stars forming and dying quickly, releasing tremendous amounts of energy through ultraviolet light, stellar winds, and supernova explosions, D’Eugenio added.
Three main hypotheses have been advanced to explain the luminosity of early galaxies. The first attributed it to supermassive black holes in these galaxies consuming material, which appears to be ruled out as the observed light is spread over a wider area than would be expected from black hole activity. The remaining hypotheses suggest that these galaxies either contain more stars than expected or that their stars are inherently brighter than those today, and further research will determine if these hold true.
