Letter | Published:

H2D+ observations give an age of at least one million years for a cloud core forming Sun-like stars

Nature volume 516, pages 219221 (11 December 2014) | Download Citation

Abstract

The age of dense interstellar cloud cores, where stars and planets form, is a crucial parameter in star formation and difficult to measure. Some models predict rapid collapse1,2, whereas others predict timescales of more than one million years (ref. 3). One possible approach to determining the age is through chemical changes as cloud contraction occurs, in particular through indirect measurements of the ratio of the two spin isomers (ortho/para) of molecular hydrogen, H2, which decreases monotonically with age4,5,6. This has been done for the dense cloud core L183, for which the deuterium fractionation of diazenylium (N2H+) was used as a chemical clock to infer7 that the core has contracted rapidly (on a timescale of less than 700,000 years). Among astronomically observable molecules, the spin isomers of the deuterated trihydrogen cation, ortho-H2D+ and para-H2D+, have the most direct chemical connections to H2 (refs 8, 9, 10, 11, 12) and their abundance ratio provides a chemical clock that is sensitive to greater cloud core ages. So far this ratio has not been determined because para-H2D+ is very difficult to observe. The detection of its rotational ground-state line has only now become possible thanks to accurate measurements of its transition frequency in the laboratory13, and recent progress in instrumentation technology14,15. Here we report observations of ortho- and para-H2D+ emission and absorption, respectively, from the dense cloud core hosting IRAS 16293-2422 A/B, a group of nascent solar-type stars (with ages of less than 100,000 years). Using the ortho/para ratio in conjunction with chemical models, we find that the dense core has been chemically processed for at least one million years. The apparent discrepancy with the earlier N2H+ work7 arises because that chemical clock turns off sooner than the H2D+ clock, but both results imply that star-forming dense cores have ages of about one million years, rather than 100,000 years.

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References

  1. 1.

    et al. An observational perspective of low-mass dense cores. II: Evolution toward the initial mass function. In Protostars and Planets V (eds , & ) 33–46 (Univ. Arizona Press, 2007)

  2. 2.

    , & Rapid star formation and global gravitational collapse. Mon. Not. R. Astron. Soc. 420, 1457–1461 (2012)

  3. 3.

    , & Observational constraints on the ages of molecular clouds and the star formation timescale: ambipolar-diffusion-controlled or turbulence-induced star formation? Astrophys. J. 646, 1043 (2006)

  4. 4.

    & On the ortho-H2/para-H2 ratio in molecular clouds. Mon. Not. R. Astron. Soc. 209, 25–31 (1984)

  5. 5.

    , & The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse. Astron. Astrophys. 449, 621–629 (2006)

  6. 6.

    , & Ortho-H2 and the age of interstellar dark clouds. Astrophys. J. 739, L35 (2011)

  7. 7.

    et al. Ortho-H2 and the age of prestellar cores. Astron. Astrophys. 551, A38 (2013)

  8. 8.

    , & The chemistry of H2D+ in cold clouds. Astron. Astrophys. 258, 479–488 (1992)

  9. 9.

    , & H3++HD → H2D++H2: low-temperature laboratory measurements and interstellar implications. Planet. Space Sci. 50, 1275–1285 (2002)

  10. 10.

    , , & Toward understanding of H3+ isotopic and nuclear spin fractionations in cold space. In Molecules in Space and Laboratory (eds & ) 119 (S. Diana, 2007)

  11. 11.

    , & H3++H2 isotopic system at low temperatures: microcanonical model and experimental study. J. Chem. Phys. 130, 164302 (2009)

  12. 12.

    et al. Modelling line emision of deuterated H3+ from prestellar cores. Astron. Astrophys. 509, A98 (2010)

  13. 13.

    et al. High-resolution rotational spectroscopy in a cold ion trap: H2D+ and D2H+. Phys. Rev. Lett. 100, 233004 (2008)

  14. 14.

    et al. GREAT: the SOFIA high-frequency heterodyne instrument. Astron. Astrophys. 542, L1 (2012)

  15. 15.

    et al. Early science with SOFIA, the Stratospheric Observatory For Infrared Astronomy. Astrophys. J. 749, L17 (2012)

  16. 16.

    & A search for the rotational transitions of H2D+ at 1370 GHz and H3O+ at 985 GHz. Astrophys. J. 405, L39–L42 (1993)

  17. 17.

    & Accurate rest frequencies of submillimeter-wave lines of H2D+ and D2H+. J. Mol. Spec. 233, 7 (2005)

  18. 18.

    et al. The Atacama Pathfinder EXperiment (APEX)—a new submillimeter facility for southern skies. Astron. Astrophys. 454, L13 (2006)

  19. 19.

    The duplicity of IRAS 16293–2422: a protobinary star? Astrophys. J. 337, 858–864 (1989)

  20. 20.

    , , , & On the origin of the molecular outflows in IRAS 16293–2422. Astrophys. J. 780, L11 (2014)

  21. 21.

    et al. Probing the early stages of low-mass star formation in LDN 1689N: dust and water in IRAS 16293–2422A, B, and E. Astrophys. J. 608, 341–364 (2004)

  22. 22.

    et al. The solar type protostar IRAS16293–2422: new constraints on the physical structure. Astron. Astrophys. 519, A65 (2010)

  23. 23.

    & Dynamics and depletion in thermally supercritical starless cores. Mon. Not. R. Astron. Soc. 402, 1625 (2010)

  24. 24.

    , & Hipparcos distance estimates of the Ophiuchus and the Lupus cloud complexes. Astron. Astrophys. 480, 785–792 (2008)

  25. 25.

    , & HD depletion in starless cores. Astron. Astrophys. 554, A92 (2013)

  26. 26.

    Non-LTE radiative transfer in clumpy molecular clouds. Astron. Astrophys. 322, 943–961 (1997)

  27. 27.

    et al. Interstellar chemistry of nitrogen hydrides in dark clouds. Astron. Astrophys. 562, A83 (2014)

  28. 28.

    et al. Survey of ortho-H2D+ (11,0-11,1) in dense cloud cores. Astron. Astrophys. 492, 703–718 (2008)

  29. 29.

    et al. The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI). Astron. Astrophys. 518, L6 (2010)

  30. 30.

    , , & Abundant H2D+ in the pre-stellar core L1544. Astron. Astrophys. 403, L37–L41 (2003)

  31. 31.

    , & From prestellar cores to protostars: the initial conditions of star formation. In Protostars and Planets IV (eds , & ) 59–96 (Univ. Arizona Press, 2000)

  32. 32.

    et al. High-resolution wide-band fast Fourier transform spectrometers. Astron. Astrophys. 542, L3 (2012)

  33. 33.

    et al. GREAT/SOFIA atmospheric calibration. Astron. Astrophys. 542, L4 (2012)

  34. 34.

    , , , & The first-light APEX submillimeter heterodyne instrument FLASH. Astron. Astrophys. 454, L21 (2006)

  35. 35.

    et al. The APEX digital Fast Fourier Transform spectrometer. Astron. Astrophys. 454, L29 (2006)

  36. 36.

    et al. Heavy water stratification in a low-mass protostar. Astron. Astrophys. 553, A75 (2013)

  37. 37.

    et al. The low-temperature nuclear spin equilibrium of H3+ in collisions with H2. Astron. Astrophys. 759, 21 (2012)

  38. 38.

    , , , & Ortho-para H2 conversion by proton exchange at low temperature: an accurate quantum mechanical study. Phys. Rev. Lett. 107 023201 (2011); Erratum: Phys. Rev. Lett. 108, 109903 (2012)

  39. 39.

    et al. Chemical modeling of L183/L134N: an estimate of the ortho/para H2 ratio. Astron. Astrophys. 494, 623–636 (2009)

  40. 40.

    et al. Chemistry in disks. IV. Benchmarking gas-grain chemical models with surface reactions. Astron. Astrophys. 522, A42 (2010)

  41. 41.

    et al. First time-dependent study of H2 and H3+ ortho-para chemistry in the diffuse ISM. Astrophys. J. 787, 44 (2014)

  42. 42.

    , , , & On the ortho:para ratio of H3+ in diffuse molecular clouds. Astrophys. J. 729, 15 (2011)

  43. 43.

    et al. From filamentary clouds to prestellar cores to the stellar IMF: initial highlights from the Herschel Gould Belt Survey. Astron. Astrophys. 518, L102 (2010)

  44. 44.

    et al. Class 0 protostars in the Perseus molecular cloud: a correlation between the youngest protostars and the dense gas distribution. Astrophys. J. 787, L18 (2014)

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Acknowledgements

GREAT is a development by the MPI für Radioastronomie and the KOSMA/Universität zu Köln, in cooperation with the MPI für Sonnensystemforschung and the DLR Institut für Planetenforschung. SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract NAS2-97001, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. APEX, the Atacama Pathfinder Experiment, is a collaboration between the Max Planck Institut für Radioastronomie (MPIfR), the Onsala Space Observatory (OSO), and the European Southern Observatory (ESO). This work has been supported by the Collaborative Research Centre 956, funded by the Deutsche Forschungsgemeinschaft (DFG). O.S. and J.H. acknowledge support from the Academy of Finland grants 132291 and 250741. P.C. acknowledges the financial support of the European Research Council (ERC; project PALs 320620).

Author information

Affiliations

  1. I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany

    • Sandra Brünken
    • , Edward T. Chambers
    • , Oskar Asvany
    • , Cornelia E. Honingh
    • , Jürgen Stutzki
    •  & Stephan Schlemmer
  2. Department of Physics, PO Box 64, 00014 University of Helsinki, Finland

    • Olli Sipilä
    •  & Jorma Harju
  3. Max-Planck Institut für Extraterrestrische Physik, Gießenbachstraße 1, 85741 Garching bei München, Germany

    • Olli Sipilä
    •  & Paola Caselli
  4. School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK

    • Paola Caselli
  5. Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

    • Tomasz Kamiński
    •  & Karl M. Menten

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Contributions

S.S., S.B., O.A., P.C., J.H., O.S. and J.S. jointly designed the study and proposed the SOFIA observations. E.T.C. performed the calibration and the analysis of the SOFIA data. C.E.H. was instrumental in developing the GREAT receiver. T.K. and K.M.M. made the APEX observations and analysed these data. O.S. carried out the chemistry and radiative transfer modelling with help from J.H. The paper was jointly written by S.B., J.H., O.S., P.C. and S.S. All authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Sandra Brünken or Stephan Schlemmer.

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https://doi.org/10.1038/nature13924

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