A large fraction of the mass of the interstellar medium in our Galaxy is in the form of warm (103–104 K) and cool (50–100 K) atomic hydrogen (H i) gas1. Cold (10–30 K) regions are thought to be dominated by dense clouds of molecular hydrogen2. Cold H i is difficult to observe, and therefore our knowledge of its abundance and distribution in the interstellar medium is poor. The few known clouds of cold H i are much smaller in size and mass than typical molecular clouds3,4,5. Here we report the discovery that the H i supershell GSH139-03-69 is very cold (10 K). It is about 2 kiloparsecs in size and as massive as the largest molecular complexes6. The existence of such an immense structure composed of cold atomic hydrogen in the interstellar medium runs counter to the prevailing view that cold gas resides almost exclusively in clouds dominated by molecular hydrogen.
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Kulkarni, S. R. & Heiles, C. in Interstellar Processes (eds Hollenbach, D. J. & Thronson, H. A.) 87–122 (Reidel, Dordrecht, 1987).
Dame, T. M., Hartmann, D. & Thaddeus, P. The Milky Way in molecular clouds: A new composite CO survey. Astrophys. J. 547, 792–813 (2001).
Gibson, S. J., Taylor, A. R., Higgs, L. A. & Dewdney, P. E. A new view of cold H i clouds in the Milky Way. Astrophys. J. 540, 851–862 (2000).
Trapero, J. et al. A cold massive interstellar cloud within 120 parsecs of the Sun: K i optical and H i radio observations. Astrophys. J. 445, 231–239 (1995).
Crutcher, R. M. & Riegel, K. W. Optical interstellar line studies of a nearby cold cloud. Astrophys. J. 188, 481–488 (1974).
Solomon, P. M., Rivolo, A. R., Barrett, J. & Yahil, A. Mass, luminosity, and line width relations of Galactic molecular clouds. Astrophys. J. 319, 730–741 (1987).
Dickey, J. M. & Lockman, F. J. H i in the Galaxy. Annu. Rev. Astron. Astrophys. 28, 215–261 (1990).
Spitzer, L. Physical Processes in the Interstellar Medium Ch. 3 (Wiley & Sons, New York, 1978).
Landecker, T. L. et al. The synthesis telescope at the Dominion Radio Astrophysical Observatory. Astron. Astrophys. Suppl. Ser. 145, 509–524 (2000).
Higgs, L. A. in New Perspectives on the Interstellar Medium (eds Taylor, A. R., Landecker, T. L. & Joncas, G.) 15–26 (Astronomical Society of the Pacific, San Francisco, 1999).
Taylor, A. R. et al. The Canadian Galactic Plane Survey. Astron J. (submitted).
Heiles, C. H i shells and supershells. Astrophys. J. 229, 533–544 (1979).
Kerr, F. J. & Lynden-Bell, D. Review of Galactic constants. Mon. Not. R. Astron. Soc. 221, 1023–1038 (1986).
Hartmann, D. & Burton, W. B. Atlas of Galactic Neutral Hydrogen (Cambridge Univ. Press, Cambridge, 1997).
Burton, W. B. in Galactic and Extragalactic Radio Astronomy (eds Verschuur, G. L. & Kellermann, K. I.) 295–358 (Springer, Berlin, 1988).
Heyer, M. H. et al. The Five College Radio Astronomy Observatory CO survey of the outer Galaxy. Astrophys. J. Suppl. Ser. 115, 241–258 (1998).
Van Dishoeck, E. F. & Black, J. H. Comprehensive models of diffuse interstellar clouds: Physical conditions and molecular abundances. Astrophys. J. Suppl. Ser. 62, 109–145 (1986).
Wannier, P. G., Lichten, S. M. & Morris, M. Warm H i halos around molecular clouds. Astrophys. J. 268, 727–738 (1983).
Blitz, L. in The Physics of Star Formation and Early Stellar Evolution (eds Lada, C. J. & Kylafis, N. D.) 3–33 (Kluwer Academic, Dordrecht, 1991).
Elmegreen, B. G. & Elmegreen, D. M. H i superclouds in the inner Galaxy. Astrophys. J. 320, 182–198 (1987).
Kulkarni, S. R., Dickey, J. M. & Heiles, C. Measurement of spin temperatures in a rapidly moving H i shell. Astrophys. J. 291, 716–721 (1985).
Heiles, C. Temperatures and their variation within interstellar H i structures. Astrophys. J. 262, 135–141 (1982).
Perna, R. & Raymond, J. Testing the multiple supernovae versus gamma-ray burst scenarios for giant H i supershells. Astrophys. J. 539, 706–711 (2000).
Tenorio-Tagle, G. & Bodenheimer, P. Large-scale expanding superstructures in galaxies. Annu. Rev. Astron. Astrophys. 26, 145–197 (1988).
Ehlerová, S., Palouš, J., Theis, Ch. & Hensler, G. Fragmentation of expanding shells in spiral and irregular galaxies. Astron. Astrophys. 328, 121–129 (1997).
Higgs, L. A & Tapping, K. F. The Low-Resolution DRAO Survey of H i emission from the Galactic plane. Astron. J. 120, 2471–2487 (2000).
We thank T. Dame for providing the CO data from ref. 2. The Canadian Galactic Plane Survey (CGPS) is a Canadian project with international partners. The Dominion Radio Astrophysical Observatory is operated as a national facility by the National Research Council of Canada. The CGPS is supported by the Natural Sciences and Engineering Research Council of Canada.
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Knee, L., Brunt, C. A massive cloud of cold atomic hydrogen in the outer Galaxy. Nature 412, 308–310 (2001). https://doi.org/10.1038/35085519