The possible disappearance of a massive star in the low-metallicity galaxy PHL 293B

Abstract

<jats:title>ABSTRACT</jats:title> <jats:p>We investigate a suspected very massive star in one of the most metal-poor dwarf galaxies, PHL 293B. Excitingly, we find the sudden disappearance of the stellar signatures from our 2019 spectra, in particular the broad H lines with P Cygni profiles that have been associated with a massive luminous blue variable (LBV) star. Such features are absent from our spectra obtained in 2019 with the Echelle Spectrograph for Rocky Exoplanet- and Stable Spectroscopic Observation and X-shooter instruments of the European Southern Observatory’s Very Large Telescope. We compute radiative transfer models using cmfgen, which fit the observed spectrum of the LBV and are consistent with ground-based and archival Hubble Space Telescope photometry. Our models show that during 2001–2011, the LBV had a luminosity L* = 2.5–3.5 × 106 L⊙, a mass-loss rate $\dot{M} = 0.005{-}0.020 ~{\rm M}_{\odot }$ yr−1, a wind velocity of 1000 km s−1, and effective and stellar temperatures of Teff = 6000–6800 and T* = 9500–15 000 K. These stellar properties indicate an eruptive state. We consider two main hypotheses for the absence of the broad emission components from the spectra obtained since 2011. One possibility is that we are seeing the end of an LBV eruption of a surviving star, with a mild drop in luminosity, a shift to hotter effective temperatures, and some dust obscuration. Alternatively, the LBV could have collapsed to a massive black hole without the production of a bright supernova.</jats:p>

Is GW190521 the merger of black holes from the first stellar generations?

“…Our Z = 0.0003 MESA models stay hot and lose 1.5 M during the post-MS, while our GENEC models can become spectroscopically similar to LBVs (Groh et al 2014). As a result, they may lose significantly more mass at that stage (7.5 M forṀ LBV,max = 2.5 × 10 −5 M yr −1 ), even at low metallicity (Smith & Owocki 2006;Allan et al 2020).…”

The search for failed supernovae with the Large Binocular Telescope: a new candidate and the failed SN fraction with 11 yr of data

“…Reynolds et al (2015) examined a sample of 15 galaxies with multi-epoch HST data and reported the discovery of NGC 3021-CANDIDATE-1, a 25-30 M yellow supergiant (YSG), which disappeared in the optical without a recorded SN. Another failed SN candidate is a luminous blue variable (LBV) in the dwarf galaxy PHL 293B (Allan et al 2020). While N6946-BH1 and NGC 3021-CANDIDATE-1 were identified by their photometry, this LBV was identified as a failed SN candidate due to the disappearance of broad emission lines, which had been present in the spectra of the object for years prior.…”

Massive Star Modeling and Nucleosynthesis

“…From an observational point of view, it is not clear whether a star that is still very massive at the end of its evolution is able to explode as a supernova or will just collapse directly into a black hole. The lack of identified massive progenitors for SN type Ibc, and the maximal mass of type II events progenitors Crockett et al, 2008;Smartt et al, 2009) suggests that above M ini ≃ 25 − 30 M ⊙ , the collapse cannot be reversed and a black hole is formed without any SN (Allan et al, 2020) or with a failed SN. The debate is still not settled to date (see for example Smartt et al, 2009;Yoon et al, 2012;Kochanek, 2014;Suzuki and Maeda, 2018;Farrell et al, 2020).…”