SNe II the rescue: Sibling supernovae as a path to test systematics in SN II cosmology

One of the most significant issues in today's cosmology is the Hubble tension, the apparent discrepancy between the early- and late-Universe Hubble constant estimates. Type II supernovae (SNe II) provide a unique path for testing this discrepancy: not only can one infer the Hubble constant with competitive precision through them, but this can be done as a single-step measurement without employing the cosmic distance ladder. This property makes them highly important for cosmology, which defines the focus of the adH0cc collaboration. High precision, however, comes hand-in-hand with the need to better understand potential systematic effects. Sibling supernovae, or SNe II, that explode in the same host galaxy, offer a unique way to test them: even though the supernovae are likely different, exploding in different environments, their distances from us should match regardless. This puts a strong constraint on the distance estimation analysis and allows us to explore if mismatches in supernova and environmental properties such as reddening, metallicity, or explosion energy lead to noticeable offsets in distances. In this presentation, I will describe our study, which was based on a literature sample of supernovae that showed that SNe II distances are, at first glance, internally consistent. Then, I will showcase the results of our follow-up study, expanding the sample of available siblings and providing a deeper glance at systematic effects.