Almost all massive stars explode as supernovae and form a black hole or neutron star. The remnant mass and the impact of the chemical yield on subsequent star formation and galactic evolution strongly depend on the internal physics of the progenitor star, which is currently not well understood. The theoretical uncertainties of stellar interiors accumulate with stellar age, which is particularly pertinent for the blue supergiant phase. Stellar oscillations represent a unique method of probing stellar interiors, yet inference for blue supergiants is hampered by a dearth of observed pulsation modes. Here we report the detection of diverse variability in blue supergiants using the K2 and TESS space missions. The discovery of pulsation modes or an entire spectrum of low-frequency gravity waves in these stars allow us to map the evolution of hot massive stars towards the ends of their lives. Future asteroseismic modelling will provide constraints on ages, core masses, interior mixing, rotation and angular momentum transport. The discovery of variability in blue supergiants is a step towards a data-driven empirical calibration of theoretical evolution models for the most massive stars in the Universe.
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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
The K2 systematics correction code k2sc is freely available and documented at https://github.com/OxES/k2sc. The iterative pre-whitening code is freely available and documented at https://github.com/IvS-KULeuven/IvSPythonRepository. The Python Markov chain Monte Carlo code emcee is freely available and documented at http://dfm.io/emcee/current/. The stellar evolution code, MESA, is freely available and documented at http://mesa.sourceforge.net/, and the stellar pulsation code, GYRE, is freely available and documented at https://bitbucket.org/rhdtownsend/gyre/wiki/Home.
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The K2 and TESS data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). Funding for the K2 mission is provided by NASA’s Science Mission Directorate. Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. The Gaia data in this paper come from the European Space Agency mission Gaia, processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France; the SAO/NASA Astrophysics Data System; and the VizieR catalogue access tool, CDS, Strasbourg, France. The research leading to these results has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 670519: MAMSIE). T.M.R., P.V.F.E. and R.P.R. received support from STFC grant ST/L005549/1 and NASA grant NNX17AB92G. S.S.-D. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) through grants AYA2015-68012-C2-1 and Severo Ochoa SEV-2015-0548, and grant ProID2017010115 from the Gobierno de Canarias. B.J.S.P. is a NASA Sagan Fellow. This work was performed in part under contract with the Jet Propulsion Laboratory funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. T.R.W. acknowledges the support of the Australian Research Council (grant DP150100250).
The authors declare no competing interests.
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Supplementary Data captions and Supplementary Figs. 1–170
Parameters of the 114 OB stars observed by the K2 space mission.
Parameters of 53 OB stars in the LMC observed by the TESS space mission.
Fit parameters of residual amplitude spectra of K2 OB stars.
Fit parameters of amplitude spectra of TESS LMC OB stars.
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Bowman, D.M., Burssens, S., Pedersen, M.G. et al. Low-frequency gravity waves in blue supergiants revealed by high-precision space photometry. Nat Astron 3, 760–765 (2019). https://doi.org/10.1038/s41550-019-0768-1