Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Nuclear-powered millisecond pulsars and the maximum spin frequency of neutron stars


Millisecond pulsars are neutron stars that are thought to have been spun-up by mass accretion from a stellar companion1. It is not known whether there is a natural brake for this process, or if it continues until the centrifugal breakup limit is reached at submillisecond periods. Many neutron stars that are accreting mass from a companion star exhibit thermonuclear X-ray bursts that last tens of seconds, caused by unstable nuclear burning on their surfaces2. Millisecond-period brightness oscillations during bursts from ten neutron stars (as distinct from other rapid X-ray variability that is also observed3,4) are thought to measure the stellar spin2,5, but direct proof of a rotational origin has been lacking. Here we report the detection of burst oscillations at the known spin frequency of an accreting millisecond pulsar, and we show that these oscillations always have the same rotational phase. This firmly establishes burst oscillations as nuclear-powered pulsations tracing the spin of accreting neutron stars, corroborating earlier evidence5,6. The distribution of spin frequencies of the 11 nuclear-powered pulsars cuts off well below the breakup frequency for most neutron-star models, supporting theoretical predictions that gravitational radiation losses can limit accretion torques in spinning up millisecond pulsars7,8,9.

Your institute does not have access to this article

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Dynamic power spectra of millisecond oscillations in an X-ray burst on 18 October 2002 from SAX J1808.4–3658.
Figure 2: Relative phase of the burst tail oscillations in SAX J1808.4–3658, and the persistent accretion-powered pulsations just before the burst, for all four bursts.


  1. Alpar, M. A., Cheng, A. F., Ruderman, M. A. & Shaham, J. A new class of radio pulsars. Nature 300, 728–730 (1982)

    ADS  Article  Google Scholar 

  2. Strohmayer, T. E. & Bildsten, L. in Compact Stellar X-Ray Sources (eds Lewin, W. H. G. & van der Klis, M.) (Cambridge Univ. Press, in the press); preprint at 〈〉 2003

    Google Scholar 

  3. van der Klis, M. Millisecond oscillations in X-ray binaries. Annu. Rev. Astron. Astrophys. 38, 717–760 (2000)

    ADS  Article  Google Scholar 

  4. Wijnands, R. et al. Kilohertz quasi-periodic X-ray brightness fluctuations from an accreting millisecond pulsar. Nature (in the press)

  5. Strohmayer, T. E. et al. Millisecond variability from an accreting neutron star system. Astrophys. J. 469, L9–L12 (1996)

    ADS  CAS  Article  Google Scholar 

  6. Strohmayer, T. E. & Markwardt, C. B. Evidence for a millisecond pulsar in 4U 1636–53 during a superburst. Astrophys. J. 577, 337–345 (2002)

    ADS  Article  Google Scholar 

  7. Wagoner, R. V. Gravitational radiation from accreting neutron stars. Astrophys. J. 278, 345–348 (1984)

    ADS  Article  Google Scholar 

  8. Bildsten, L. Gravitational radiation and rotating neutron stars. Astrophys. J. 501, L89–L93 (1998)

    ADS  Article  Google Scholar 

  9. Andersson, N., Kokkotas, K. D. & Stergioulas, N. On the relevance of the r-mode instability for accreting neutron stars and white dwarfs. Astrophys. J. 516, 307–314 (1999)

    ADS  Article  Google Scholar 

  10. Strohmayer, T. E., Jahoda, K., Giles, A. B. & Lee, U. Millisecond pulsations from a low-mass X-ray binary system in the Galactic center region. Astrophys. J. 486, 355–362 (1997)

    ADS  Article  Google Scholar 

  11. Cumming, A. & Bildsten, L. Rotational evolution during type I X-ray bursts. Astrophys. J. 544, 453–474 (2000)

    ADS  CAS  Article  Google Scholar 

  12. in't Zand, J. J. et al. Discovery of the X-ray transient SAX J1808.4–3658, a likely low-mass X-ray binary. Astron. Astrophys. 331, L25–L28 (1998)

    ADS  Google Scholar 

  13. Wijnands, R. & van der Klis, M. A millisecond pulsar in an X-ray binary system. Nature 394, 344–346 (1998)

    ADS  CAS  Article  Google Scholar 

  14. Chakrabarty, D. & Morgan, E. H. The two-hour orbit of a binary millisecond X-ray pulsar. Nature 394, 346–348 (1998)

    ADS  CAS  Article  Google Scholar 

  15. in't Zand, J. J. et al. The first outburst of SAX J1808.4–3658 revisited. Astron. Astrophys. 372, 916–921 (2001)

    ADS  Article  Google Scholar 

  16. Muno, M. P., Chakrabarty, D., Galloway, D. K. & Psaltis, D. The frequency stability of millisecond oscillations in thermonuclear X-ray bursts. Astrophys. J. 580, 1048–1059 (2002)

    ADS  Article  Google Scholar 

  17. Wijnands, R., Strohmayer, T. & Franco, L. M. Discovery of nearly coherent oscillations with a frequency of 567 Hz during type I X-ray bursts of the X-ray transient and eclipsing binary X1658–298. Astrophys. J. 549, L71–L75 (2001)

    ADS  Article  Google Scholar 

  18. Galloway, D. K., Chakrabarty, D., Muno, M. P. & Savov, P. Discovery of a 270 hertz X-ray burst oscillation in the X-ray dipper 4U 1916–053. Astrophys. J. 549, L85–L88 (2001)

    ADS  Article  Google Scholar 

  19. Markwardt, C. B., Swank, J. H., Strohmayer, T. E., in't Zand, J. J. M. & Marshall, F. E. Discovery of a second millisecond accreting pulsar: XTE J1751–305. Astrophys. J. 575, L21–L24 (2002)

    ADS  Article  Google Scholar 

  20. Galloway, D. K., Chakrabarty, D., Morgan, E. H. & Remillard, R. A. Discovery of a high-latitude accreting millisecond pulsar in an ultracompact binary. Astrophys. J. 576, L137–L140 (2002)

    ADS  Article  Google Scholar 

  21. Markwardt, C. B., Smith, E. & Swank, J. H. XTE J1807–294. IAU Circ. No. 8080 (2003).

  22. Cumming, A., Zweibel, E. & Bildstenm, L. Magnetic screening in accreting neutron stars. Astrophys. J. 557, 958–966 (2001)

    ADS  Article  Google Scholar 

  23. Spitkovsky, A., Levin, Y. & Ushomirsky, G. Propagation of thermonuclear flames on rapidly rotating neutron stars: Extreme weather during type I X-ray bursts. Astrophys. J. 566, 1018–1038 (2002)

    ADS  Article  Google Scholar 

  24. Cook, G. B., Shapiro, S. L. & Teukolsky, S. A. Recycling pulsars to millisecond periods in general relativity. Astrophys. J. 421, L117–L120 (1994)

    ADS  Article  Google Scholar 

  25. Haensel, P., Lasota, J. P. & Zdunik, J. L. On the minimum period of uniformly rotating neutron stars. Astron. Astrophys. 344, 151–153 (1999)

    ADS  Google Scholar 

  26. Backer, D. C., Kulkarni, S. R., Heiles, C. E., Davis, M. M. & Goss, W. M. A millisecond pulsar. Nature 300, 615–618 (1982)

    ADS  Article  Google Scholar 

  27. Cook, G. B., Shapiro, S. L. & Teukolsky, S. A. Rapidly rotating neutron stars in general relativity: Realistic equations of state. Astrophys. J. 424, 823–845 (1994)

    ADS  Article  Google Scholar 

  28. Psaltis, D. & Chakrabarty, D. The disk-magnetosphere interaction in the accretion-powered millisecond pulsar SAX J1808.4–3658. Astrophys. J. 521, 332–340 (1999)

    ADS  Article  Google Scholar 

  29. Camilo, F., Thorsett, S. E. & Kulkarni, S. R. The magnetic fields, ages, and original spin periods of millisecond pulsars. Astrophys. J. 421, L15–L18 (1994)

    ADS  Article  Google Scholar 

  30. Bildsten, L. in Radio Pulsars (eds Bailes, M., Nice, D. J. & Thorsett, S. E.) (Astronomical Society of the Pacific, San Francisco, in the press); preprint at 〈〉 (2002).

Download references


We thank L. Bildsten, F. Lamb, D. Psaltis and S. Thorsett for discussions. This work was supported in part by NASA and the Alfred P. Sloan Foundation.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Deepto Chakrabarty.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Chakrabarty, D., Morgan, E., Muno, M. et al. Nuclear-powered millisecond pulsars and the maximum spin frequency of neutron stars. Nature 424, 42–44 (2003).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing