Luminous fast blue optical transients as very massive star core-collapse events

¹ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC) Keplerlaan 1 2201 AZ Noordwijk, The Netherlands
² Department of Astrophysics/IMAPP, Radboud University PO Box 9010 6500 GL Nijmegen, The Netherlands
³ Department of Physics, University of Warwick Gibbet Hill Road CV4 7AL Coventry, United Kingdom
⁴ School of Natural Sciences, Institute for Advanced Study 1 Einstein Drive Princeton NJ 08540, USA

^★★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 3 October 2025
Accepted: 29 December 2025

Abstract

Context. Luminous fast blue optical transients (LFBOTs) are rare extragalactic events of unknown origin. Tidal disruption events (TDEs) involving white dwarfs by intermediate mass black holes (BHs), mergers of BHs and Wolf-Rayet (WR) stars, and failed supernovae (SNe) are among the proposed explanations.

Aims. In this paper, we explore the viability of very massive star core-collapse (CC) events as the origin of LFBOTs. The appeal of such a model is that the formation of massive BHs via CC events could yield observational signatures that can match the disparate lines of evidence that point towards both CC and TDE origins for LFBOTs.

Methods. We explored the formation rate of massive BHs in binary population synthesis models and compared the metallicities of their progenitors with the observed metallicities of LFBOT host galaxies. We further examined the composition, mass-loss rates, and fallback masses of these stars, placing them in the context of LFBOT observations.

Results. We determined the formation rate of BHs with masses greater than ∼30–40 M_⊙ to be similar to the observed LFBOT rate. The stars producing these BHs are biased towards a low metallicity (Z < 0.3 Z_⊙) and they are H- and He-poor, with dense circumstellar media. However, some LFBOTs have host galaxies with higher metallicities than predicted and they typically have denser local environments (plausibly due to late stage mass loss not captured in the models). We find that long-lived emission from an accretion disc (as implicated in the prototypical LFBOT AT 2018cow) can only be produced in these events under maximal disc mass and angular momentum conditions.

Conclusions. We conclude that a (very) massive star CC scenario is a plausible explanation for at least some LFBOTs, but it still faces challenges. The preferred progenitors for LFBOTs in the failed SN interpretation overlap with those predicted to produce super-kilonovae (super-KNe). We therefore suggest that LFBOTs are promising targets in the search for super-KNe and that they could offer a non-negligible contribution to the r-process enrichment of galaxies.