Astronomers using NASA's James Webb Space Telescope have discovered a mature spiral galaxy resembling the Milky Way, formed just 1.5 billion years after the Big Bang. Named Alaknanda, this grand-design spiral challenges theories on galaxy formation timelines. The find highlights a more dynamic early Universe than previously thought.
In a surprising observation, researchers Rashi Jain and Yogesh Wadadekar from the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research in Pune, India, identified the galaxy Alaknanda through JWST data. This galaxy, visible in the direction of the Abell 2744 cluster, benefits from gravitational lensing that amplifies its light, making details clearer. Alaknanda features two prominent spiral arms around a bright central bulge, spanning about 30,000 light-years, and shows rapid star formation at a rate equivalent to 60 solar masses per year—20 times faster than the Milky Way's current pace. Roughly half its stars formed in just 200 million years.
The discovery defies expectations, as grand-design spirals were thought to need billions of years to develop through processes like gas accretion and density waves. "Alaknanda has the structural maturity we associate with galaxies that are billions of years older," Jain stated. This early organization suggests galaxy assembly occurred more efficiently than models predict.
Observations from JWST's UNCOVER and MegaScience surveys, using up to 21 filters, allowed precise measurements of Alaknanda's distance, dust content, and star formation history. Named after a Himalayan river and the Hindi term for the Milky Way, the galaxy's existence points to a Universe capable of quick structure-building. "Alaknanda reveals that the early Universe was capable of far more rapid galaxy assembly than we anticipated," Wadadekar noted. Future studies with JWST spectroscopy or ALMA could clarify its disk dynamics and arm formation, possibly from cold gas inflows or companion interactions.
Published in Astronomy & Astrophysics (2025, 703: A96), this find adds to evidence of advanced early galaxies, reshaping views on cosmic evolution and the origins of stars and planets.