The 2026 Kavli Prize in Astrophysics goes to Vasily Belokurov, Amina Helmi and Rodrigo Ibata for discovering the “fossil” remains of ancient galaxy collisions that built the Milky Way. Using huge star catalogues and precision measurements from surveys such as the Sloan Digital Sky Survey (SDSS) and the Gaia space mission, the laureates identified stellar streams and remnants — including the major Gaia–Enceladus Sausage event — that prove our Galaxy formed by swallowing smaller galaxies. Their work turns the Milky Way into a readable history book: the motions and chemistry of stars record past mergers and let astronomers trace where different stars came from and how dark matter shaped the Galaxy.
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Discovery
The three researchers established clear observational evidence that the Milky Way experienced major merger events whose signatures remain visible today.
Methods
They combined 3-D positions and velocities with chemical abundances from surveys (SDSS, Gaia) and advanced modelling to identify groups of stars moving together and to trace them back to their parent systems.
Notable findings
- Belokurov mapped the “field of streams” and highlighted the role of ultra-faint dwarfs and the Gaia–Enceladus Sausage as a dominant ancient merger.
- Helmi identified stellar streams and showed ancient mergers still leave detectable signatures in the local halo.
- Ibata discovered and mapped the Sagittarius Dwarf Spheroidal Galaxy and revealed complex tidal debris around the Milky Way.
Implications
The results change our view of galaxies from static spiral disks to evolving systems shaped by violent collisions. The stellar streams also act as “seismometers” for the Galaxy’s gravitational field, helping to measure the unseen dark matter distribution.
More about
The official Kavli Prize website (external link)