Researchers using ALMA have discovered a distant galaxy, Y1, that existed about 800 million years after the Big Bang and was forming stars at roughly 180 solar masses per year — about 180 times the Milky Way's rate. ALMA’s Band 9 measured the galaxy's dust at about −180°C (−356°F), warmer than dust seen in similar early galaxies. A small amount of warm dust can appear as bright as a larger mass of cold dust, which may resolve puzzling high dust estimates in primordial systems. The team will pursue higher-resolution ALMA observations to find more such star factories and study rapid early galaxy growth.
‘Superheated’ Star Factory in the Early Universe Produced Stars 180× Faster Than the Milky Way
Researchers using ALMA have discovered a distant galaxy, Y1, that existed about 800 million years after the Big Bang and was forming stars at roughly 180 solar masses per year — about 180 times the Milky Way's rate. ALMA’s Band 9 measured the galaxy's dust at about −180°C (−356°F), warmer than dust seen in similar early galaxies. A small amount of warm dust can appear as bright as a larger mass of cold dust, which may resolve puzzling high dust estimates in primordial systems. The team will pursue higher-resolution ALMA observations to find more such star factories and study rapid early galaxy growth.
11:36 AM, 11/18/2025Science
Superheated stellar nursery from 800 million years after the Big Bang
Astronomers have identified an exceptionally hot, early-universe galaxy — nicknamed Y1 — that was forming stars at a prodigious rate roughly 180 solar masses per year, about 180 times the Milky Way's present-day rate. The galaxy existed approximately 800 million years after the Big Bang, and its light has been traveling to Earth for about 13 billion years.
How the discovery was made
The team measured the temperature of Y1's cosmic dust using the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA’s Band 9 receiver and its 66 antennas on the Chajnantor plateau in northern Chile allowed the researchers to detect the thermal emission from dust in this distant galaxy and determine that the dust is radiating at about −180°C (−356°F) — considerably warmer than dust seen in comparable primordial galaxies.
“We are looking back to an epoch when the universe was making stars much faster than it does today,” said team leader Tom Bakx of Chalmers University of Technology. “Earlier observations had already detected dust in this galaxy — the most distant direct detection of glowing dust to date — which suggested Y1 might be a different, superheated kind of star factory. To confirm that, we measured its dust temperature.”
Why the warm dust matters
Warm dust emits much more strongly per unit mass than cold dust. That means a relatively small amount of hot dust can appear as bright as a large mass of cool dust, potentially explaining why some primordial galaxies seem unexpectedly dusty given their young stellar populations. As Laura Sommovigo of the Flatiron Institute and Columbia University explains, the brightness of Y1 could be produced by modest quantities of warm dust rather than by enormous dust masses that young galaxies should not yet be able to produce.
Implications and next steps
Y1’s intense starburst — roughly 180 solar masses per year at the time we observe it — is likely a brief phase in the galaxy’s evolution, but such episodes may have been common in the early universe and have played an important role in rapid galaxy growth. The finding also ties into questions about how the first generations of stars (Population III) formed under conditions very different from those that make stars like the Sun today.
The team plans follow-up ALMA observations at higher resolution to study Y1’s internal structure and to search for more examples of these hot star factories. The research was published on Nov. 12 in the Monthly Notices of the Royal Astronomical Society.
People and instruments
Key contributors include Tom Bakx (Chalmers University of Technology), Yoichi Tamura (Nagoya University), and Laura Sommovigo (Flatiron Institute and Columbia University). The discovery relied on ALMA’s sensitivity and its Band 9 instrument to measure faint, distant dust emission.