Stockholm university

Seán BrennanPost doctor

About me

Massive stars live for millions of years and end their lives in seconds when they undergo core collapse.

Understanding which massive stars will undergo core collapse is an almost impossible task. However, in the past 20 years, a growing sample of massive stars has shown some energetic activity in the years before a core-collapse supernova is observed, typically found by looking at historical observations.

My current work is centered on identifying these outbursts from massive stars in real-time, in the weeks to months before they end their lives as core-collapse supernovae, with the ultimate goal of obtaining spectral observations. Although this attempts to predict the future, recent results show that massive star progenitors can be highly unstable in their final moments, providing strong evidence of shells of dense material colliding with previously ejected material, which is likely the main powering mechanism for these events.

Understanding the reason for this instability shortly before core collapse is unclear; however, this work highlights an exciting new area of transient astronomy

Research projects


A selection from Stockholm University publication database

  • Spectroscopic observations of progenitor activity 100 days before a Type Ibn supernova

    2024. Seán J. Brennan (et al.). Astronomy and Astrophysics 684


    Obtaining spectroscopic observations of the progenitors of core-collapse supernovae is often unfeasible, due to an inherent lack of knowledge as to what stars experience supernovae and when they will explode. In this Letter we present photometric and spectroscopic observations of the progenitor activity of SN 2023fyq before the He-rich progenitor explodes as a Type Ibn supernova. The progenitor of SN 2023fyq shows an exponential rise in flux prior to core collapse. Complex He I emission line features are observed in the progenitor spectra, with a P Cygni-like profile, as well as an evolving broad base with velocities of the order of 10 000 km s−1. The luminosity and evolution of SN 2023fyq is consistent with a Type Ibn, reaching a peak r-band magnitude of −18.8 mag, although there is some uncertainty regarding the distance to the host, NGC 4388, which is located in the Virgo cluster. We present additional evidence of asymmetric He-rich material being present both prior to and after the explosion of SN 2023fyq, which suggests that this material survived the ejecta interaction. Broad [O I], C I, and the Ca II triplet lines are observed at late phases, confirming that SN 2023fyq was a genuine supernova, rather than a non-terminal interacting transient. SN 2023fyq provides insight into the final moments of a massive star’s life, demonstrating that the progenitor is likely highly unstable before core collapse.

    Read more about Spectroscopic observations of progenitor activity 100 days before a Type Ibn supernova

Show all publications by Seán Brennan at Stockholm University