Early galaxies spun at just 50 km/s, much slower than today’s Milky Way.
Key Takeaways
- The youngest rotating galaxy ever measured, MACS1149-JD1, spins far slower than modern galaxies.
- Early galaxies were small and rotated slowly, gaining speed and size over billions of years.
- MACS1149-JD1, only 3,000 light-years wide, existed when the universe was just 500 million years old.
- The galaxy’s slow rotation, at 50 km/s, is a quarter of the Milky Way’s speed.
- Gravitational lensing and ALMA observations made this groundbreaking discovery possible.
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Unlocking Galactic Evolution: A Slow-Spinning Galaxy in the Early Universe
Astronomers from Waseda University have made an unprecedented discovery: the youngest galaxy ever measured with a rotational speed, MACS1149-JD1, reveals that galaxies in the early universe rotated much slower than today’s massive spirals. Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the team observed this galaxy, which existed when the universe was just 500 million years old.
Due to its extreme distance, MACS1149-JD1 is typically too dim to study. However, its light is magnified by gravitational lensing from a massive galaxy cluster, allowing astronomers to detect it. They focused on doubly ionized oxygen (O III) within the galaxy’s disk, modeling its rotation speed and size. Their findings, published in The Astrophysical Journal Letters, show that MACS1149-JD1 is just 3,000 light-years wide—tiny compared to the Milky Way’s 100,000 light-year span.
A Galaxy in Its Infancy
The analysis revealed that MACS1149-JD1 rotates at a modest 50 km/s, far slower than the Milky Way’s 200+ km/s speed. Co-author Akio K. Inoue explained that this suggests the galaxy is in the initial stages of developing rotational motion. The results support the idea that galaxies start small and spin slowly, gradually building mass and speed over billions of years.
These observations are pivotal in understanding how galaxies evolve over cosmic time. Future studies using advanced instruments like the James Webb Space Telescope could further illuminate how rotation rates change throughout the universe’s history, helping to refine our models of galactic formation and development.
