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JWST Reveals 'Alaknanda,' a Milky Way–Like Spiral 1.5 Billion Years After the Big Bang

Leveraging gravitational lensing, an NCRA‑TIFR team reports the find in Astronomy & Astrophysics and plans spectroscopic follow-up to uncover the galaxy’s dynamics and formation.

Overview

  • Identified behind the Abell 2744 cluster, the galaxy’s light was magnified, allowing clear imaging of two symmetric spiral arms and a central bulge.
  • Photometric analysis across up to 21 JWST filters (UNCOVER and MegaScience surveys) places the system at roughly redshift 4 with unusually mature structure for its epoch.
  • The galaxy spans about 30,000 light-years, holds roughly ten billion solar masses in stars, and forms new stars at about 60 solar masses per year.
  • Roughly half of its stellar mass appears to have formed within about 200 million years, indicating rapid assembly that challenges standard formation timelines.
  • Researchers are seeking JWST NIRSpec and ALMA observations to measure rotation and turbulence and to test whether the disk is dynamically cold or hot, distinguishing between steady accretion and tidal-triggered origins.