Anomalously Fast Core and Envelope Rotation in Red Giants
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1.
Tata Institute of Fundamental Research
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2.
Rutherford Appleton Laboratory
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3.
New York University Abu Dhabi
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4.
National Astronomical Observatory of Japan
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5.
California Institute of Technology
Abstract
Red giants undergo dramatic and complex structural transformations as they evolve. Angular momentum is transported between the core and envelope during this epoch, a poorly understood process. Here, we infer envelope and core rotation rates from Kepler observations of ∼1517 red giants. While many measurements are consistent with the existing studies, our investigation reveals systematic changes in the envelope-to-core rotation ratio and we report the discovery of anomalies such as clump stars with rapidly rotating cores and red giants with envelopes rotating faster than their cores. We propose binary interactions as a possible mechanism by which some of these cores and envelopes are spun up. These results pose challenges to current theoretical expectations and can have major implications for compact remnants born from stellar cores.
Copyright and License
© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
S.D. acknowledges SERB, DST, Government of India, CII, and Intel Technology India Pvt. Ltd. for the Prime Minister’s fellowship and facilitating research. All computations are performed on Intel® Xeon® Platinum 8280 CPU. We thank Dhiraj D. Kalamkar, Intel Technology India Pvt. Ltd. for suggestions which helped optimize the neural-network training. This paper includes data collected by the Kepler mission and obtained from the MAST data archive at the Space Telescope Science Institute (STScI) from the Kepler/KIC repository (STScI 2011). Funding for the Kepler mission is provided by the NASA Science Mission Directorate. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This research made use of Lightkurve, a Python package for Kepler and TESS data analysis (Lightkurve Collaboration et al. 2018).
Funding
This research was supported in part by a generous donation (from the Murty Trust) aimed at enabling advances in astrophysics through the use of machine learning. Murty Trust, an initiative of the Murty Foundation, is a not-for-profit organization dedicated to the preservation and celebration of culture, science, and knowledge systems born out of India. The Murty Trust is headed by Mrs. Sudha Murty and Mr. Rohan Murty.
Contributions
S.M.H., S.D., and O.B. conceived the idea. O.B. developed the power spectra simulations. S.D. built the training data set, developed the neural network, and analyzed Kepler data, with numerous inputs from O.B. and S.M.H. O.B. and S.D. worked on the MCMC analysis. J.F. developed the theoretical models. All authors reviewed the manuscript.
Software References
pytorch, lightkurve, MESA.
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Dhanpal_2025_ApJ_988_224.pdf
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Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2506.06415 (arXiv)
Funding
- Science and Engineering Research Board
- Department of Science and Technology
- National Aeronautics and Space Administration
- NAS 5-26555
Dates
- Accepted
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2025-06-05
- Available
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2025-07-25Published online