Abstract

Type Ia supernovae (SNe Ia) are a cornerstone of modern cosmology, yet their use as standardisable candles is limited by an unresolved dependence on their host galaxies: SNe Ia in high-mass galaxies are brighter than those in low-mass galaxies. This effect remains the dominant source of uncertainty in supernova cosmology and may be driving the ongoing Hubble Tension.

In this talk, I will highlight how studies of supernova siblings (multiple SNe Ia in the same host) provide a powerful way to isolate environmental effects. By comparing supernovae that share a common host but explode in different local environments, siblings help disentangle global and local drivers of SN Ia luminosity. I will present recent results from my sibling analyses and discuss how this approach will inform improved SN Ia standardisation in this new era of large transient surveys.