Kraft break

In astronomy, the Kraft break refers to the abrupt decrease in stars' average rotation rates at surface temperatures below about 6,500 Kelvin.[1] This temperature corresponds to mid-F type stars.[2] The so-called break bears the name of astronomer Robert Kraft,[3] though its existence was recognized prior to his publications on the topic.[4]

The break is understood to separate stars with deep convective envelopes and efficient magnetic dynamos from those without. The dynamos are thought to maintain magnetic fields that transfer angular momentum to the stellar wind, thus slowing down the star's surface through magnetic braking. In hot stars the process is less efficient (because the convective envelopes are shallow) so the stars continue to rotate quickly.[5]

The Kraft break coincides with a transition in hot Jupiters' spin-orbit alignment. Hot Jupiters orbiting cooler stars tend to orbit in the same plane as stellar rotation, while those orbiting hotter stars are more likely to be misaligned.[1]

References

  1. 1 2 Wang 汪, Xian-Yu 宪钰; Wang 王, Songhu 松虎; Ong 王, J. M. Joel 加冕 (2026-01-01). "Unified Kraft Break at ∼6500 K: A Newly Identified Single-star Obliquity Transition Matches the Classical Rotation Break". The Astrophysical Journal Letters. 996 (1): L7. arXiv:2511.15610. Bibcode:2026ApJ...996L...7W. doi:10.3847/2041-8213/ae21c5. ISSN 2041-8205.
  2. ↑ Beyer, Alexa C.; White, Russel J. (2024-09-01). "The Kraft Break Sharply Divides Low-mass and Intermediate-mass Stars". The Astrophysical Journal. 973 (1): 28. arXiv:2408.02638. Bibcode:2024ApJ...973...28B. doi:10.3847/1538-4357/ad6b0d. ISSN 0004-637X.
  3. ↑ Kraft, Robert P. (1967). "Studies of Stellar Rotation. V. The Dependence of Rotation on Age among Solar-Type Stars". The Astrophysical Journal. 150: 551. Bibcode:1967ApJ...150..551K. doi:10.1086/149359. ISSN 0004-637X. Retrieved 2026-08-19.
  4. ↑ Schatzman, E. (1962). "A theory of the role of magnetic activity during star formation". Annales d'Astrophysique. 25: 18. Bibcode:1962AnAp...25...18S.
  5. ↑ Maeder, A. (2009), Physics, Formation and Evolution of Rotating Stars (PDF), Astronomy and Astrophysics Library, Bibcode:2009pfer.book.....M, doi:10.1007/978-3-540-76949-1, ISBN 978-3-540-76948-4


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