Fading into Darkness: A Weak Mass Ejection and Low-efficiency Fallback Accompanying Black Hole Formation in M31-2014-DS1

Year: 2026 DOI: 10.3847/2041-8213/ae468d
Stellar-mass black holes (BHs) can form from the near-complete collapse of massive stars, causing them to abruptly disappear. The star M31-2014-DS1 in the Andromeda galaxy was reported to exhibit such a disappearance between 2014 and 2022, with properties consistent with the failed explosion of an ≈12–13 M⊙ yellow supergiant leading to the formation of an ≈5 M⊙ BH. We present mid-infrared (MIR) observations of the remnant obtained with the James Webb Space Telescope (JWST) and X-ray observations from the Chandra X-ray Observatory in 2024. The JWST Mid-infrared Instrument/NIRSpec data reveal an extremely red source, showing strong blueshifted absorption from molecular gas (CO, CO₂, H₂O, SO₂) and deep silicate dust features. Modeling the dust continuum confirms continued bolometric fading of the central source to log (L/L⊙) ≈ 3.88 (≈7%–8% of the progenitor luminosity), surrounded by a dust shell spanning ≈40–200 au. Modeling of the molecular gas indicates ∼0.1 M⊙ of gas expanding at ≈100 km s−1 near the inner edge of the dust shell. No X-ray source is detected down to a luminosity limit of LX ≲ 1.5 × 10³⁵ erg s−1. We show that the panchromatic observations are explained by (i) a low-energy (≈10⁴⁶ erg) ejection of the outer H-rich progenitor envelope and (ii) a fading central BH powered by inefficient (∼0.1% in mass) accretion of loosely bound fallback material. The analysis robustly establishes the bolometric fading of M31-2014-DS1 following its >30 yr archival record of constant optical/infrared brightness, and provides the first cohesive insights into BH formation via low-energy explosions and long-term fallback.