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Ubiquitous aromatic carbon chemistry at the earliest stages of star formation

Abstract

Benzonitrile (c-C6H5CN, where ā€˜cā€™ indicates a cyclic structure), a polar proxy for benzene (c-C6H6), has the potential to serve as a highly convenient radio probe for aromatic chemistry, provided that this ring can be found in other astronomical sources beyond the molecule-rich prestellar cloud TMC-1. Here we present radio astronomical evidence of benzonitrile in four other prestellar, and possibly protostellar, sources: Serpens 1A, Serpens 1B, Serpens 2 and MC27/L1521F. These detections establish that benzonitrile is not unique to TMC-1; rather, aromatic chemistry appears to be widespread throughout the earliest stages of star formation, probably persisting at least until the initial formation of a protostar. The abundance of benzonitrile far exceeds predictions from models that well reproduce the abundances of carbon chains such as HC7N, a cyanpolyyne with the same heavy atoms, indicating that the chemistry responsible for planar carbon structures (as opposed to linear ones) in primordial sources is favourable but not well understood. The abundance of benzonitrile relative to carbon chain molecules displays sizable variations between sources within the Taurus and Serpens clouds, implying the importance of physical conditions and initial elemental reservoirs of the clouds themselves.

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Fig. 1: Velocity-stacked spectra of C6H5CN and the impulse response function of the stacked spectra in the five sources observed here.
Fig. 2: Simulated abundances with respect to hydrogen from NAUTILUS chemical models for C6H6 and C6H5CN in comparison to that derived for C6H5CN from observations in the five sources studied here.
Fig. 3: Derived abundance ratios between HC7N, HC9N and C6H5CN for each of the five sources studied here.
Fig. 4: Simulated abundances and abundance ratios from NAUTILUS chemical models over a range of gas and grain temperatures, gas densities and initial elemental oxygen abundances.

Data availability

The datasets analysed during the current study are available in the Green Bank Telescope archive (https://archive.nrao.edu/archive/advquery.jsp). A user manual for their reduction and analysis is also available (https://go.nature.com/3npRxW5). For the ARKHAM survey, the complete, reduced survey data are available in the Harvard Dataverse Archive50. For the GOTHAM survey, the complete, reduced survey data in the X band are available as supplementary information in ref.ā€‰37. The individual portions of the reduced spectra used in the analysis of the individual species presented here are available in the Harvard Dataverse Archive49.

Code availability

All codes used in the MCMC fitting and stacking analysis presented in this paper are open source and publicly available at https://github.com/ryanaloomis/TMC1_mcmc_fitting.

References

  1. Leger, A. & Puget, J. L. Identification of the ā€˜unidentifiedā€™ IR emission features of interstellar dust? Astron. Astrophys. 137, L5ā€“L8 (1984).

    ADSĀ  Google ScholarĀ 

  2. Allamandola, L. J., Tielens, A. G. G. M. & Barker, J. R. Polycyclic aromatic hydrocarbons and the unidentified infrared emission bands: auto exhaust along the Milky Way! Astrophys. J. 290, L25ā€“L28 (1985).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  3. Tielens, A. G. G. M. Interstellar polycyclic aromatic hydrocarbon molecules. Annu. Rev. Astron. Astrophys. 46, 289ā€“337 (2008).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  4. Gauba, G. & Parthasarathy, M. Circumstellar dust shells of hot post-AGB stars. Astron. Astrophys. 417, 201ā€“215 (2004).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  5. Bregman, J. D. & Temi, P. Gas-phase polycyclic aromatic hydrocarbons in absorption toward protostellar sources? Astrophys. J. 554, 126ā€“131 (2001).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  6. Smith, J. D. T. et al. The mid-infrared spectrum of star-forming galaxies: global properties of polycyclic aromatic hydrocarbon emission. Astrophys. J. 656, 770ā€“791 (2007).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  7. McGuire, B. A. 2018 census of interstellar, circumstellar, extragalactic, protoplanetary disk, and exoplanetary molecules. Astrophys. J. Suppl. Ser. 239, 17 (2018).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  8. Thaddeus, P., Vrtilek, J. M. & Gottlieb, C. A. Laboratory and astronomical identification of cyclopropenylidene, C3H2. Astrophys. J. 299, L63ā€“L66 (1985).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  9. Vrtilek, J. M., Gottlieb, C. A. & Thaddeus, P. Laboratory and astronomical spectroscopy of C3H2, the first interstellar organic ring. Astrophys. J. 314, 716ā€“725 (1987).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  10. Foing, B. H. & Ehrenfreund, P. Detection of two interstellar absorption bands coincident with spectral features of C60+. Nature 369, 296ā€“298 (1994).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  11. Foing, B. H. & Ehrenfreund, P. New evidences for interstellar C60+. Astron. Astrophys. 317, L59ā€“L62 (1997).

    ADSĀ  Google ScholarĀ 

  12. Cernicharo, J. et al. Infrared Space Observatoryā€™s discovery of C4H2, C6H2, and benzene in CRL 618. Astrophys. J. 546, L123ā€“L126 (2001).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  13. Cami, J., Bernard-Salas, J., Peeters, E. & Malek, S. E. Detection of C60 and C70 in a young planetary nebula. Science 329, 1180ā€“1182 (2010).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  14. BernƩ, O., Mulas, G. & Joblin, C. Interstellar C60+. Astron. Astrophys. 550, L4 (2013).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  15. McGuire, B. A. et al. Detection of the aromatic molecule benzonitrile (c-C6H5CN) in the interstellar medium. Science 359, 202ā€“205 (2018).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  16. Balucani, N. et al. Crossed beam reaction of cyano radicals with hydrocarbon molecules. I. Chemical dynamics of cyanobenzene (C6H5CN; X1A1) and perdeutero cyanobenzene (C6D5CN; X1A1) formation from reaction of CN (X2Ī£+) with benzene C6H6 (X1A1g), and d6-benzene C6D6 (X1A1g). J. Chem. Phys. 111, 7457ā€“7471 (1999).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  17. Trevitt, A., Goulay, F., Taatjes, C., Osborn, D. & Leone, S. Reactions of the CN radical with benzene and toluene: product detection and low-temperature kinetics. J. Phys. Chem. A 114, 1749ā€“55 (2010).

    ArticleĀ  Google ScholarĀ 

  18. Lee, K. L. K., McGuire, B. A. & McCarthy, M. C. Gas-phase synthetic pathways to benzene and benzonitrile: a combined microwave and thermochemical investigation. Phys. Chem. Chem. Phys. 21, 2946ā€“2956 (2019).

    ArticleĀ  Google ScholarĀ 

  19. Cooke, I. R., Gupta, D., Messinger, J. P. & Sims, I. R. Benzonitrile as a proxy for benzene in the cold ISM: low temperature rate coefficients for CN + C6H6. Astrophys. J. Lett. 891, L41 (2020).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  20. Cordiner, M. A. & Charnley, S. B. Gas-grain models for interstellar anion chemistry. Astrophys. J. 749, 120 (2012).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  21. Loomis, R. A. et al. Non-detection of HC11N towards TMC-1: constraining the chemistry of large carbon-chain molecules. Mon. Not. R. Astron. Soc. 463, 4175ā€“4183 (2016).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  22. Burkhardt, A. M. et al. Detection of HC5N and HC7N Isotopologues in TMC-1 with the Green Bank Telescope. Mon. Not. R. Astron. Soc. 474, 5068ā€“5075 (2018).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  23. Shingledecker, C. N., Tennis, J., Le Gal, R. & Herbst, E. On cosmic-ray-driven grain chemistry in cold core models. Astrophys. J. 861, 20 (2018).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  24. Kaifu, N. et al. A 8.8ā€“50 GHz complete spectral line survey toward TMC-1 I. Survey data. Publ. Astron. Soc. Jpn 56, 69ā€“173 (2004).

  25. Gratier, P. et al. A new reference chemical composition for TMC-1. Astrophys. J. Suppl. Ser. 225, 25 (2016).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  26. Cherchneff, I., Barker, J. R. & Tielens, Ae. G. G. M. Polycyclic Aromatic Hydrocarbon Formation in Carbon-rich Stellar Envelopes. Astrophys. J. 401, 269 (1992).

  27. Phillips, D. H. Polycyclic aromatic hydrocarbons in the diet. Mutat. Res. 443, 139ā€“147 (1999).

    ArticleĀ  Google ScholarĀ 

  28. Kim, K.-H., Jahan, S. A. & Kabir, E. A review of diseases associated with household air pollution due to the use of biomass fuels. J. Hazard. Mater. 192, 425ā€“431 (2011).

    ArticleĀ  Google ScholarĀ 

  29. Garrod, R. T. A three-phase chemical model of hot cores: the formation of glycine. Astrophys. J. 765, 60 (2013).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  30. Sakai, N., Shiino, T., Hirota, T., Sakai, T. & Yamamoto, S. Long carbon-chain molecules and their anions in the starless core. Lupus-1A. Astrophys. J. 718, L49ā€“L52 (2010).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  31. Friesen, R. K. et al. Abundant cyanopolyynes as a probe of infall in the Serpens South cluster-forming region. Mon. Not. R. Astron. Soc. 436, 1513ā€“1529 (2013).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  32. Hincelin, U. et al. Oxygen depletion in dense molecular clouds: a clue to a low O2 abundance? Astron. Astrophys. 530, A61 (2011).

    ArticleĀ  Google ScholarĀ 

  33. Majumdar, L. et al. Chemistry of TMC-1 with multiply deuterated species and spin chemistry of H2, H2+, H3+ and their isotopologues. Mon. Not. R. Astron. Soc. 466, 4470ā€“4479 (2016).

    ADSĀ  Google ScholarĀ 

  34. McGuire, B. A. et al. Detection of interstellar HC5O in TMC-1 with the Green Bank Telescope. Astrophys. J. Lett. 843, L28 (2017).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  35. Loomis, R. A. et al. An investigation of spectral line stacking techniques and application to the detection of HC11N. Nat. Astron. https://doi.org/10.1038/s41550-020-01261-4 (2020).

  36. Bourke, T. L. et al. The Spitzer c2d survey of nearby dense cores. II. Discovery of a low-luminosity object in the ā€œevolved starless coreā€ L1521F. Astrophys. J. 649, L37ā€“L40 (2006).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  37. McGuire, B. A. et al. Early science from GOTHAM: project overview, methods, and the detection of interstellar propargyl cyanide (HCCCH2CN) in TMC-1. Astrophys. J. Lett. 900, L10 (2020).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  38. Morgan, M. et al. A K-band spectroscopic focal plane array for the Robert C. Byrd Green Bank radio telescope. In Union Radio Scientifique Internationale XXIX General Assembly J02p1 (URSI, 2008).

  39. Roshi, D. A. et al. Advanced multi-beam spectrometer for the Green Bank Telescope. In XXXth URSI General Assembly and Scientific Symposium 1ā€“4 (URSI, 2011).

  40. Wohlfart, K., Schnell, M., Grabow, J.-U. & KĆ¼pper, J. Precise dipole moment and quadrupole coupling constants of benzonitrile. J. Mol. Spectrosc. 247, 119ā€“121 (2008).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  41. Ruaud, M., Wakelam, V. & Hersant, F. Gas and grain chemical composition in cold cores as predicted by the Nautilus three-phase model. Mon. Not. R. Astron. Soc. 459, 3756ā€“3767 (2016).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  42. McCarthy, M. C. et al. Interstellar detection of the highly polar five-membered ring cyanocyclopentadiene. Nat. Astron. https://doi.org/10.1038/s41550-020-01213-y (2020).

  43. Xue, C. et al. Detection of interstellar HC4NC and an investigation of isocyanopolyyne chemistry in TMC-1 conditions. Astrophys. J. Lett. 900, L9 (2020).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  44. Remijan, A. J., Hollis, J. M., Snyder, L. E., Jewell, P. R. & Lovas, F. J. Methyltriacetylene (CH3C6H) toward TMC-1: the largest detected symmetric top. Astrophys. J. 643, L37ā€“L40 (2006).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  45. Chabot, M., BĆ©roff, K., Dartois, E., Pino, T. & Godard, M. Coulomb explosion of polycyclic aromatic hydrocarbons induced by heavy cosmic rays: carbon chains production rates. Astrophys. J. 888, 17 (2019).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  46. Rapacioli, M. et al. Formation and destruction of polycyclic aromatic hydrocarbon clusters in the interstellar medium. Astron. Astrophys. 460, 519ā€“531 (2006).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  47. Montillaud, J., Joblin, C. & Toublanc, D. Evolution of polycyclic aromatic hydrocarbons in photodissociation regions: hydrogenation and charge states. Astron. Astrophys. 552, A15 (2013).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  48. Turner, B. E. A molecular line survey of Sagittarius B2 and Orion-KL from 70 to 115 GHz. II: analysis of the data. Astrophys. J. Suppl. Ser. 76, 617ā€“686 (1991).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  49. GOTHAM Collaboration. Spectral Stacking Data for Phase 1 Science Release of GOTHAM. Harvard Dataverse https://doi.org/10.7910/DVN/PG7BHO (2020).

  50. ARKHAM Collaboration. Spectral Stacking Data for Phase 1 Science Release of ARKHAM. Harvard Dataverse https://doi.org/10.7910/DVN/E7MMCA (2020).

  51. McEwan, M. J. et al. New H and H2 reactions with small hydrocarbon ions and their roles in benzene synthesis in dense interstellar clouds. Astrophys. J. 513, 287ā€“293 (1999).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  52. Burkhardt, A. M. et al. Modeling C-shock chemistry in isolated molecular outflows. Astrophys. J. 881, 32 (2019).

    ArticleĀ  ADSĀ  Google ScholarĀ 

  53. Jones, B. M. et al. Formation of benzene in the interstellar medium. Proc. Natl Acad. Sci. USA 108, 452ā€“457 (2011).

    ArticleĀ  ADSĀ  Google ScholarĀ 

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Acknowledgements

A.M.B. acknowledges support from the Smithsonian Institution as a Submillimeter Array Fellow. C.N.S. thanks the Alexander von Humboldt Stiftung/Foundation for their support. A.M.B. and C.N.S. also thank V. Wakelam for the use of the NAUTILUS v1.1 code. M.C.M and K.L.K.L. acknowledge financial support from NSF grant numbers AST-1908576 and AST-1615847, and NASA grant number 80NSSC18K0396. Support for B.A.M. was provided by NASA through Hubble Fellowship grant number HST-HF2-51396 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract number NAS5-26555. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Green Bank Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

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All authors contributed to the design of the GOTHAM and ARKHAM survey and helped to revise the manuscript. A.M.B and B.A.M. performed the astronomical observations and subsequent analysis. R.A.L., K.L.K.L. and B.A.M. performed the spectral fitting analyses. A.M.B. and C.N.S. contributed to or undertook the astronomical modelling and simulations. A.M.B., M.C.M. and B.A.M. wrote the manuscript with the help of C.N.S.

Corresponding authors

Correspondence to Andrew M. Burkhardt or Brett A. McGuire.

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Peer review information Nature Astronomy thanks Bernard Foing and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1ā€“11, Tables 1ā€“12 and Discussion.

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Burkhardt, A.M., Loomis, R.A., Shingledecker, C.N. et al. Ubiquitous aromatic carbon chemistry at the earliest stages of star formation. Nat Astron 5, 181ā€“187 (2021). https://doi.org/10.1038/s41550-020-01253-4

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