KANAZAWA — The James Webb Space Telescope has observed a galaxy named LAP1-B that existed 800 million years after the Big Bang, making it the most metal-poor galaxy in the early universe detected to date. The oxygen abundance in LAP1-B is just 1/240th that of the Sun.
LAP1-B exhibits an elevated carbon-to-oxygen ratio consistent with theoretical models of material dispersed by explosions of Population III stars—the first generation of stars formed from only hydrogen and helium. The galaxy has an estimated mass of less than 3,300 solar masses and is dominated by a dark matter halo.
Observations of LAP1-B were made possible by gravitational lensing from an intervening galaxy cluster, which magnified its light by a factor of 100. A research team conducted 30 hours of deep spectroscopy to characterize the galaxy’s properties.
The study detailing these findings was published in the journal Nature on May 13. Kimihiko Nakajima, associate professor at Kanazawa University and leader of the research team, said, "I was instantly thrilled by the extreme lack of oxygen revealed in the data. Finding a galaxy in such a primitive state is astonishing. It's a chemical signature that clearly indicates a primordial galaxy caught in the moments shortly after its formation." He added, "Usually, we act like 'cosmic archaeologists,' trying to guess the past by looking at old stars in our own neighborhood. But now, we can analyze the gas directly from the original scene 13 billion years ago."
LAP1-B closely resembles Ultra-Faint Dwarf galaxies (UFDs) found near the Milky Way today. Masami Ouchi, professor at NAOJ/University of Tokyo and a member of the research team, said, "UFDs are not only the faintest galaxies; they are composed of ancient stars over 12 billion years old and are often described as 'fossils of the universe.' Astronomers suspected they might be the remains of the universe's earliest galaxies because they lack heavy elements, but astronomers never had a direct link — until we found LAP1-B. It is a profound surprise to find that LAP1-B looks exactly like the 'ancestor' we had only imagined in theories. This helps us solve the mystery of why these cosmic fossils have survived in their current form to the present day." The discovery provides a direct observational link between early galaxies formed during the Epoch of Reionization and modern Ultra-Faint Dwarf galaxies.