The standard candles used to measure the size of the universe changed their fundamental nature 5 billion years ago.
April 29, 2026
Original Paper
SN Ia Population Machine. I and Unified Cosmological Simulation-Binary Synthesis Framework Establishing Non-universal Delay-time Distributions and Cosmic Progenitor-channel Dominance Crossover
arXiv · 2604.24846
The Takeaway
Type Ia supernovae are not a single, universal type of explosion as astronomers long believed. New simulations show that the dominant way these stars explode shifted from one star feeding off another to two stars colliding. This transition happened about 5.2 billion years ago, right as the universe's expansion began to accelerate. If the candles used to measure cosmic distance are actually different at different times, our maps of the universe might be slightly off. This finding forces a major recalibration of how we measure dark energy and the ultimate fate of the cosmos.
From the abstract
We present a forward-modeling framework for synthesizing Type Ia supernova (SN Ia) populations by coupling cosmological hydrodynamic simulations to binary population synthesis (BPS). Using IllustrisTNG star particles as simple stellar populations, we generate binaries and evolve them with COMPAS to produce synthetic SNe Ia tagged with explosion times and progenitor channels (single- and double-degenerate; SD and DD). This cosmology-BPS pipeline enables self-consistent, end-to-end tracking of SN