Cosmic expansion decelerating after age-bias correction

A team of astronomers at Yonsei University on Thursday published an analysis arguing that the expansion of the universe has already begun to slow, challenging the prevailing view that cosmic expansion is accelerating under a constant dark energy. The paper, published in Monthly Notices of the Royal Astronomical Society and led by YoungWook Lee, draws on observations of roughly 300 host galaxies and contends that a systematic bias tied to the ages of stars that produce Type Ia supernovae alters distance measurements used to infer expansion history.

Type Ia supernovae have long served as standard candles in cosmology because their intrinsic brightness was thought to be uniform. That uniformity underpinned the 1998 conclusion that the universe’s expansion is accelerating, a discovery recognized with the 2011 Nobel Prize in Physics. Lee and colleagues say their expanded dataset reveals a strong correlation between standardized supernova magnitudes and the ages of their progenitor stellar populations. After applying an age-bias correction, the authors report that the corrected supernova distances no longer fit the standard Lambda cold dark matter model with a cosmological constant,...