In recent years, scientists have used the NASA James Webb Space Telescope to explore the period known as Cosmic Dawn, which occurred in the first few hundred million years after the Big Bang. During this time, the first galaxies were born, providing crucial insights into the early universe. In October 2023 and January 2024, an international team of astronomers used Webb to observe galaxies as part of the JWST Advanced Deep Extragalactic Survey program. They used Webb’s NIRSpec to obtain a spectrum of a galaxy observed only 290 million years after the Big Bang, corresponding to a record-breaking redshift of about 14.
The team of astronomers discovered a galaxy with strong evidence of being above a redshift of 14 in early 2023, which was surprising due to its brightness and proximity to another galaxy. Further observations in October 2023 with Webb’s NIRCam filters supported the high-redshift hypothesis. In January 2024, NIRSpec observed the galaxy, known as JADES-GS-z14-0, for almost ten hours, confirming its redshift of 14.32 and shattering the previous most-distant galaxy record. The discovery was incredibly exciting for the team, as the galaxy’s luminosity and size indicated that most of the light came from young stars rather than a supermassive black hole.
The data revealed that the galaxy’s color was not as blue as expected, suggesting the presence of dust even at these early times. Observations with Webb’s MIRI also detected the galaxy at longer wavelengths, indicating the presence of strong ionized gas emission from hydrogen and oxygen. The presence of oxygen in such an early galaxy was surprising and suggested the existence of multiple generations of massive stars. Combined, these observations painted a picture of a galaxy that did not fit the predicted models and simulations of early universe galaxies, indicating a previously unseen level of diversity at Cosmic Dawn.
These observations were part of Guaranteed Time Observations programs, with the MIRI observations providing further insights into the galaxy’s properties. The discovery of JADES-GS-z14-0 has profound implications for our understanding of early universe galaxies and the predicted number of bright galaxies at Cosmic Dawn. Astronomers expect to find more luminous galaxies, possibly even earlier in cosmic history, in the coming years with the James Webb Space Telescope. This unprecedented diversity of galaxies at Cosmic Dawn challenges existing theories and opens new avenues for exploration in the study of the early universe.
