A Keio University-led research team, working with the National Astronomical Observatory of Japan, has precisely measured the cosmic microwave background radiation (CMB) temperature at redshift z=0.89, corresponding to about 7 billion years ago, by analyzing archival Atacama Large Millimeter/submillimeter Array (ALMA) data targeting the quasar PKS1830-211.
The CMB is faint primordial radiat by Riko Seibo
Tokyo, Japan (SPX) Nov 01, 2025
A Keio University-led research team, working with the National Astronomical Observatory of Japan, has precisely measured the cosmic microwave background radiation (CMB) temperature at redshift z=0.89, corresponding to about 7 billion years ago, by analyzing archival Atacama Large Millimeter/submillimeter Array (ALMA) data targeting the quasar PKS1830-211.
The CMB is faint primordial radiation from the recombination epoch about 380,000 years after the Big Bang, discovered accidentally in 1965 when Arno Penzias and Robert Wilson detected unexplained microwave noise. These findings cemented the Big Bang as the leading theory for the origin of the universe and ruled out rival models. Decades of research - including satellite missions like COBE, WMAP, and Planck - have confirmed the CMB's nearly perfect blackbody spectrum and mapped its tiny fluctuations, which trace the seeds of cosmic structure.
The CMB temperature is currently about 2.7 K, almost uniform throughout space but with minute variations that reveal crucial information about the universe's composition, geometry, and expansion rate. These details have enabled cosmologists to reconstruct the universe's history, including the exact proportions of ordinary matter, dark matter, and dark energy.
The ALMA team, led by doctoral student Tatsuya Kotani and Professor Tomoharu Oka, determined the CMB temperature at z=0.89 to be 5.13 +/- 0.06 K, marking the most precise value ever achieved at an intermediate redshift. This finding demonstrates that the CMB temperature increases predictably with redshift, providing a lasting and robust test of the standard cosmological model, known as Lambda-CDM. That model successfully explains the universe's evolution, from the Big Bang to present, via dark energy, cold dark matter, and general relativity.
This new measurement further confirms the model's predictions, enabling researchers to constrain the thermal history and test for any exotic physics that would alter the cooling of the universe. The discovery underscores the CMB's role as a cosmic "fossil record" and backbone of precision cosmology. The findings were published in The Astrophysical Journal on October 29, 2025.
Research Report:Record-Precision Measurement of the Cosmic Microwave Background Temperature at z = 0.89
Related Links
Keio University
Understanding Time and Space