Letter | Published:

Discovery of two young brown dwarfs in an eclipsing binary system

Nature volume 440, pages 311314 (16 March 2006) | Download Citation



Brown dwarfs are considered to be ‘failed stars’ in the sense that they are born with masses between the least massive stars (0.072 solar masses, M)1 and the most massive planets (0.013M)2; they therefore serve as a critical link in our understanding of the formation of both stars and planets3. Even the most fundamental physical properties of brown dwarfs remain, however, largely unconstrained by direct measurement. Here we report the discovery of a brown-dwarf eclipsing binary system, in the Orion Nebula star-forming region, from which we obtain direct measurements of mass and radius for these newly formed brown dwarfs. Our mass measurements establish both objects as brown dwarfs, with masses of 0.054 ± 0.005M and 0.034 ± 0.003M. At the same time, with radii relative to the Sun's of 0.669 ± 0.034R and 0.511 ± 0.026R, these brown dwarfs are more akin to low-mass stars in size. Such large radii are generally consistent with theoretical predictions for young brown dwarfs in the earliest stages of gravitational contraction4,5. Surprisingly, however, we find that the less-massive brown dwarf is the hotter of the pair; this result is contrary to the predictions of all current theoretical models of coeval brown dwarfs.

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  1. 1.

    & Theory of low-mass stars and substellar objects. Annu. Rev. Astron. Astrophys. 38, 337–377 (2000)

  2. 2.

    , , & The theory of brown dwarfs and extrasolar giant planets. Rev. Mod. Phys. 73, 719–765 (2001)

  3. 3.

    Observations of brown dwarfs. Annu. Rev. Astron. Astrophys. 38, 485–519 (2000)

  4. 4.

    , , & Evolutionary models for solar metallicity low-mass stars: mass-magnitude relationships and colour-magnitude diagrams. Astron. Astrophys. 337, 403–412 (1998)

  5. 5.

    & Evolution of low mass stars. Mem. Soc. Astron. It. 68, 807–822 (1997)

  6. 6.

    et al. Dynamical masses of the binary brown dwarf GJ 569 Bab. Astrophys. J. 615, 958–971 (2004)

  7. 7.

    Accurate masses and radii of normal stars. Astron. Astrophys. Rev. 3, 91–126 (1991)

  8. 8.

    & Realization of accurate close-binary light curves: application to MR Cygni. Astrophys. J. 166, 605–620 (1971)

  9. 9.

    & A computational guide to physics of eclipsing binaries. I. Demonstrations and perspectives. Astrophys. J. 628, 426–438 (2005)

  10. 10.

    , , & Evolutionary models for very low-mass stars and brown dwarfs with dusty atmospheres. Astrophys. J. 542, 464–472 (2000)

  11. 11.

    & Rotation and variability of very low mass stars and brown dwarfs near epsilon Ori. Astron. Astrophys. 429, 1007–1023 (2005)

  12. 12.

    & Rotation and activity in mid-M to L field dwarfs. Astrophys. J. 583, 451–472 (2003)

  13. 13.

    , , , & Dynamical mass constraints on low-mass pre-main-sequence stellar evolutionary tracks: an eclipsing binary in Orion with a 1.0 M primary and a 0.7 M secondary. Astrophys. J. Suppl. 151, 357–385 (2004)

  14. 14.

    The late-M dwarfs. Astron. J. 101, 662–676 (1991)

  15. 15.

    , & The spectroscopically determined substellar mass function of the Orion Nebula cluster. Astrophys. J. 610, 1045–1063 (2004)

  16. 16.

    & An assessment of dynamical mass constraints on pre-main-sequence evolutionary tracks. Astrophys. J. 604, 741–757 (2004)

  17. 17.

    , & Near-infrared photometric variability of stars toward the Orion A molecular cloud. Astron. J. 121, 3160–3190 (2001)

  18. 18.

    & The Orion molecular cloud and star-forming region. Annu. Rev. Astron. Astrophys. 27, 41–85 (1989)

  19. 19.

    et al. Accretion, kinematics, and rotation in the Orion Nebula Cluster: Initial results from Hectochelle. Astron. J. 129, 363–381 (2005)

  20. 20.

    On the stellar population and star-forming history of the Orion Nebula Cluster. Astron. J. 113, 1733–1768 (1997)

  21. 21.

    & Star formation in the Orion Nebula Cluster. Astrophys. J. 525, 772–783 (1999)

  22. 22.

    et al. A planet-sized transiting star around OGLE-TR-122. Accurate mass and radius near the hydrogen-burning limit. Astron. Astrophys. 433, L21–L24 (2005)

  23. 23.

    & The formation of brown dwarfs as ejected stellar embryos. Astron. J. 122, 432–439 (2001)

  24. 24.

    & The origin of the initial mass function and its dependence on the mean Jeans mass in molecular clouds. Mon. Not. R. Astron. Soc. 356, 1201–1221 (2005)

  25. 25.

    , & The formation mechanism of brown dwarfs. Mon. Not. R. Astron. Soc. 332, L65–L68 (2002)

  26. 26.

    & On the frequency of close binary systems among very low-mass stars and brown dwarfs. Mon. Not. R. Astron. Soc. 362, L45–L49 (2005)

  27. 27.

    , & Measuring fundamental parameters of substellar objects. II. Masses and radii. Astrophys. J. 609, 885–905 (2004)

  28. 28.

    et al. Measuring fundamental parameters of substellar objects. I. Surface gravities. Astrophys. J. 609, 854–884 (2004)

  29. 29.

    & A spectroscopic technique for measuring stellar properties of pre-main-sequence stars. Astron. J. 126, 3030–3042 (2003)

  30. 30.

    , & Stellar properties of pre-main-sequence stars from high-resolution near-infrared spectra. Astron. J. 126, 3043–3057 (2003)

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We are grateful to I. Baraffe, G. Basri, D. Golimowski, and D. Weintraub for discussions, and to D. Gudehaus and A. Prsa for software used in our analyses. This work is supported by grants to K.G.S. and R.D.M. from the National Science Foundation. The Gemini Observatory is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (USA), the Particle Physics and Astronomy Research Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina).

Author information


  1. Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, USA

    • Keivan G. Stassun
  2. Department of Astronomy, University of Wisconsin—Madison, Madison, Wisconsin 53706, USA

    • Robert D. Mathieu
  3. Space Telescope Science Institute, Baltimore, Maryland 21218, USA

    • Jeff A. Valenti


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Competing interests

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

Corresponding author

Correspondence to Keivan G. Stassun.

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  1. 1.

    Supplementary Figure 1

    The geometry of the orbit is shown both as it appears from Earth and as it would appear if seen from above, at four different times in the orbit. Also shown is the relationship between the orbital geometry and the diminutions of light that occur when the brown dwarfs eclipse one another.

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