Letter | Published:

Soft equations of state for neutron-star matter ruled out by EXO 0748 - 676

Naturevolume 441pages11151117 (2006) | Download Citation

Subjects

Abstract

The interiors of neutron stars contain matter at very high densities, in a state that differs greatly from those found in the early Universe or achieved in terrestrial experiments1. Matter in these conditions can only be probed through astrophysical observations that measure the mass and radius of neutron stars with sufficient precision2. Here I report a determination of the mass and radius of the neutron star EXO 0748 - 676 that appears to rule out all the soft equations of state of neutron-star matter. If this object is typical, then condensates2 and unconfined quarks1 do not exist in the centres of neutron stars.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

References

  1. 1

    Hands, S. The phase diagram of QCD. Contemp. Phys. 42, 209–225 (2001)

  2. 2

    Lattimer, J. M. & Prakash, M. The physics of neutron stars. Science 304, 536–542 (2004)

  3. 3

    Gottwald, M., Haberl, F., Parmar, A. N. & White, N. E. The bursting behaviour of the transient X-ray burst source EXO 0748 - 676—A dependence between the X-ray burst properties and the strength of the persistent emission. Astrophys. J. 308, 213–224 (1986)

  4. 4

    Wolff, M. T., Becker, P. A., Ray, P. S. & Wood, K. S. A strong X-ray burst from the low mass X-ray binary EXO 0748 - 676. Astrophys. J. 632, 1099–1103 (2005)

  5. 5

    Lewin, W. H. G., van Paradijs, J. & Taam, R. in X-ray Bursts X-ray Binaries (eds Lewin, W. H. G., van den Heuvel, E. P. J. & van Paradijs, J.) (University Press, Cambridge, 1995)

  6. 6

    Cottam, J., Paerels, F. & Mendez, M. Gravitationally redshifted absorption lines in the X-ray burst spectra of a neutron star. Nature 420, 51–54 (2002)

  7. 7

    Özel, F. & Psaltis, D. Spectral lines from rotating neutron stars. Astrophys. J. 582, L31–L34 (2003)

  8. 8

    Madej, J., Joss, P. C. & Różańska, A. Model atmospheres and X-ray spectra of bursting neutron stars: hydrogen-helium comptonized spectra. Astrophys. J. 602, 904–912 (2004)

  9. 9

    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)

  10. 10

    Loeb, A. Spectroscopic constraints on the surface magnetic field of the accreting neutron star EXO 0748 - 676. Phys. Rev. Lett. 91, 071103 (2004)

  11. 11

    Galloway, D. K., Psaltis, D., Chakrabarty, D. & Muno, M. P. Eddington-limited X-ray bursts as distance indicators. I. Systematic trends and spherical symmetry in bursts from 4U 1728 - 34. Astrophys. J. 590, 999–1007 (2003)

  12. 12

    Galloway, D. K., Muno, M. P., Chakrabarty, D., Psaltis, D. & Hartman, J. M. Thermonuclear bursts observed by RXTE: the MIT catalogue. HEAD 8.2520G (2004)

  13. 13

    Strohmayer, T. E., Zhang, W. & Swank, J. H. 363 Hz oscillations during the rising phase of bursts from 4U 1728 - 34: Evidence for rotational modulation. Astrophys. J. 487, L77–L80 (1997)

  14. 14

    Damen, E. et al. X-ray bursts with photospheric radius expansion and the gravitational redshift of neutron stars. Astron. Astrophys. 237, 103–109 (1990)

  15. 15

    Muno, M. P., Özel, F. & Chakrabarty, D. The amplitude evolution and harmonic content of millisecond oscillations in thermonuclear X-ray bursts. Astrophys. J. 581, 550–561 (2002)

  16. 16

    Villarreal, A. R. & Strohmayer, T. E. Discovery of the neutron star spin frequency in EXO 0748 - 676. Astrophys. J. 614, L121–L124 (2004)

  17. 17

    Lattimer, J. M. & Prakash, M. Neutron star structure and the equation of state. Astrophys. J. 550, 426–442 (2001)

  18. 18

    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)

  19. 19

    Dey, M., Bombau, I., Dey, J., Ray, S. & Samanta, B. C. Strange stars with realistic quark vector interaction and phenomenological density-dependent scalar potential. Phys. Lett. B 438, 123–128 (1998)

  20. 20

    Chang, P., Morsink, S., Bildsten, L. & Wasserman, I. Rotational broadening of atomic spectral features from neutron stars. Astrophys. J. 636, L117–L120 (2006)

Download references

Acknowledgements

I am grateful to the γ-ray group, especially C. Kouveliotou, for their hospitality at MSFC where this idea was born; and for the hospitality of the members of Anton Pannekoek Institute at the University of Amsterdam, where the work was completed. I thank D. Psaltis for useful discussions and comments on the manuscript.

Author information

Affiliations

  1. Department of Physics, University of Arizona, Tucson, 1118 E. 4th Street, Arizona, 85704, USA

    • F. Özel

Authors

  1. Search for F. Özel in:

Competing interests

Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The author declares no competing financial interests.

Corresponding author

Correspondence to F. Özel.

About this article

Publication history

Received

Accepted

Issue Date

DOI

https://doi.org/10.1038/nature04858

Further reading

Comments

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.