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Diffuse Galactic antimatter from faint thermonuclear supernovae in old stellar populations


Our Galaxy hosts the annihilation of a few 1043 low-energy positrons every second. Radioactive isotopes capable of supplying such positrons are synthesized in stars, stellar remnants and supernovae. For decades, however, there has been no positive identification of a main stellar positron source, leading to suggestions that many positrons originate from exotic sources like the Galaxy’s central supermassive black hole or dark matter annihilation. Here we show that a single type of transient source, deriving from stellar populations of age 3–6 Gyr and yielding 0.03 M of the positron emitter 44Ti, can simultaneously explain the strength and morphology of the Galactic positron annihilation signal and the Solar System abundance of the 44Ti decay product 44Ca. This transient is likely the merger of two low-mass white dwarfs, observed in external galaxies as the sub-luminous, thermonuclear supernova known as SN 1991bg-like.

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Figure 1: Binned CO white dwarf–He white dwarf mergers within our BPS model.
Figure 2: SFRs of the disk and bulge adopted in this work and resulting SN Ia and SN 91bg formation rates vSN.
Figure 3: Constraints on the characteristic delay time tp of the main source of Galactic positrons.
Figure 4: Modelled white dwarf masses and inferred synthesized masses of 56Ni and 44Ti.


  1. 1

    Johnson, W. N. III, Harnden, F. R. Jr & Haymes, R. C. The spectrum of low-energy gamma radiation from the galactic-center region. Astrophys. J. Lett. 172, 1–7 (1972).

    ADS  Article  Google Scholar 

  2. 2

    Prantzos, N. et al. The 511 keV emission from positron annihilation in the Galaxy. Rev. Mod. Phys. 83, 1001–1056 (2011).

    ADS  Article  Google Scholar 

  3. 3

    Bland-Hawthorn, J. & Gerhard, O. The galaxy in context: structural, kinematic, and integrated properties. Annu. Rev. Astron. Astrophys. 54, 529–596 (2016).

    ADS  Article  Google Scholar 

  4. 4

    Aharonian, F. A. & Atoyan, A. M. On the origin of the galactic annihilation radiation. Sov. Astron. Lett. 7, 395–398 (1981).

    ADS  Google Scholar 

  5. 5

    Beacom, J. F. & Yüksel, H. Stringent constraint on galactic positron production. Phys. Rev. Lett. 97, 071102 (2006).

    ADS  Article  Google Scholar 

  6. 6

    Alexis, A., Jean, P., Martin, P. & Ferrière, K. Monte Carlo modelling of the propagation and annihilation of nucleosynthesis positrons in the Galaxy. Astron. Astrophys. 564, A108 (2014).

    ADS  Article  Google Scholar 

  7. 7

    Churazov, E., Sazonov, S., Tsygankov, S., Sunyaev, R. & Varshalovich, D. Positron annihilation spectrum from the Galactic Centre region observed by SPI/INTEGRAL revisited: annihilation in a cooling ISM? Mon. Not. R. Astron. Soc. 411, 1727–1743 (2011).

    ADS  Article  Google Scholar 

  8. 8

    Siegert, T. et al. Gamma-ray spectroscopy of positron annihilation in the Milky Way. Astron. Astrophys. 586, A84 (2016).

    Article  Google Scholar 

  9. 9

    Roques, J. P. et al. SPI/INTEGRAL in-flight performance. Astron. Astrophys. 411, L91–L100 (2003).

    ADS  Article  Google Scholar 

  10. 10

    Skinner, G., Diehl, R., Zhang, X., Bouchet, L. & Jean, P. In Proc. 10th INTEGRAL Workshop: A Synergistic View of the High-Energy Sky (INTEGRAL 2014) 054 (2014);

  11. 11

    Launhardt, R., Zylka, R. & Mezger, P. G. The nuclear bulge of the Galaxy. III. Large-scale physical characteristics of stars and interstellar matter. Astron. Astrophys. 384, 112–138 (2002).

    ADS  Article  Google Scholar 

  12. 12

    Higdon, J. C., Lingenfelter, R. E. & Rothschild, R. E. The galactic positron annihilation radiation and the propagation of positrons in the interstellar medium. Astrophys. J. 698, 350–379 (2009).

    ADS  Article  Google Scholar 

  13. 13

    Guessoum, N., Jean, P. & Prantzos, N. Microquasars as sources of positron annihilation radiation. Astron. Astrophys. 457, 753–762 (2006).

    ADS  Article  Google Scholar 

  14. 14

    Siegert, T. et al. Positron annihilation signatures associated with the outburst of the microquasar V404 Cygni. Nature 531, 341–343 (2016).

    ADS  Article  Google Scholar 

  15. 15

    Chan, K.-W. & Lingenfelter, R. E. Positrons from supernovae. Astrophys. J. 405, 614–636 (1993).

    ADS  Article  Google Scholar 

  16. 16

    Leloudas, G. et al. The normal Type Ia SN 2003hv out to very late phases. Astron. Astrophys. 505, 265–279 (2009).

    ADS  Article  Google Scholar 

  17. 17

    Kerzendorf, W. E., Taubenberger, S., Seitenzahl, I. R. & Ruiter, A. J. Very late photometry of SN 2011fe. Astrophys. J. Lett. 796, 26–30 (2014).

    ADS  Article  Google Scholar 

  18. 18

    Graur, O. et al. Late-time photometry of Type Ia supernova SN 2012cg reveals the radioactive decay of 57Co. Astrophys. J. 819, 31 (2016).

    ADS  Article  Google Scholar 

  19. 19

    Bouchet, L., Jourdain, E. & Roques, J.-P. The galactic 26Al emission map as revealed by INTEGRAL SPI. Astrophys. J. 801, 142 (2015).

    ADS  Article  Google Scholar 

  20. 20

    Troja, E. et al. Swift/BAT detection of hard X-rays from Tycho’s supernova remnant: evidence for titanium-44. Astrophys. J. Lett. 797, L6 (2014).

    ADS  Article  Google Scholar 

  21. 21

    The, L.-S. et al. Are 44Ti-producing supernovae exceptional? Astron. Astrophys. 450, 1037–1050 (2006).

    ADS  Article  Google Scholar 

  22. 22

    Timmes, F. X., Woosley, S. E., Hartmann, D. H. & Hoffman, R. D. The production of 44Ti and 60Co in supernovae. Astrophys. J. 464, 332–341 (1996).

    ADS  Article  Google Scholar 

  23. 23

    Leising, M. D. & Share, G. H. Gamma-ray limits on galactic 60Fe and 44Ti nucleosynthesis. Astrophys. J. 424, 200–207 (1994).

    ADS  Article  Google Scholar 

  24. 24

    Hansen, C. J. Element production in simple helium burning. Astrophys. J. 169, 585–588 (1971).

    ADS  Article  Google Scholar 

  25. 25

    Woosley, S. E., Taam, R. E. & Weaver, T. A. Models for Type I supernova. I – detonations in white dwarfs. Astrophys. J. 301, 601–623 (1986).

    ADS  Article  Google Scholar 

  26. 26

    Karakas, A. I., Ruiter, A. J. & Hampel, M. R coronae borealis stars are viable factories of pre-solar grains. Astrophys. J. 809, 184 (2015).

    ADS  Article  Google Scholar 

  27. 27

    Belczynski, K. et al. Compact object modeling with the StarTrack population synthesis code. Astrophys. J. Suppl. 174, 223–260 (2008).

    ADS  Article  Google Scholar 

  28. 28

    Pakmor, R., Kromer, M., Taubenberger, S. & Springel, V. Helium-ignited violent mergers as a unified model for normal and rapidly declining Type Ia supernovae. Astrophys. J. Lett. 770, L8 (2013).

    ADS  Article  Google Scholar 

  29. 29

    Dan, M., Guillochon, J., Brüggen, M., Ramirez-Ruiz, E. & Rosswog, S. Thermonuclear detonations ensuing white dwarf mergers. Mon. Not. R. Astron. Soc. 454, 4411–4428 (2015).

    ADS  Article  Google Scholar 

  30. 30

    Filippenko, A. V. et al. The subluminous, spectroscopically peculiar Type IA supernova 1991bg in the elliptical galaxy NGC 4374. Astron. J. 104, 1543–1556 (1992).

    ADS  Article  Google Scholar 

  31. 31

    Perets, H. B. et al. A faint type of supernova from a white dwarf with a helium-rich companion. Nature 465, 322–325 (2010).

    ADS  Article  Google Scholar 

  32. 32

    Li, W. et al. Nearby supernova rates from the Lick Observatory Supernova Search – III. The rate-size relation, and the rates as a function of galaxy Hubble type and colour. Mon. Not. R. Astron. Soc. 412, 1473–1507 (2011).

    ADS  Article  Google Scholar 

  33. 33

    Howell, D. A. The progenitors of subluminous Type Ia supernovae. Astrophys. J. Lett. 554, 193–196 (2001).

    ADS  Article  Google Scholar 

  34. 34

    González-Gaitán, S. et al. Subluminous Type Ia supernovae at high redshift from the Supernova Legacy Survey. Astrophys. J. 727, 107 (2011).

    ADS  Article  Google Scholar 

  35. 35

    Piro, A. L., Thompson, T. A. & Kochanek, C. S. Reconciling 56Ni production in Type Ia supernovae with double degenerate scenarios. Mon. Not. R. Astron. Soc. 438, 3456–3464 (2014).

    ADS  Article  Google Scholar 

  36. 36

    Waldman, R. et al. Helium shell detonations on low-mass white dwarfs as a possible explanation for SN 2005E. Astrophys. J. 738, 21 (2011).

    ADS  Article  Google Scholar 

  37. 37

    van Dokkum, P. G. et al. The assembly of Milky-Way-like galaxies since z ~ 2.5. Astrophys. J. Lett. 771, L35 (2013).

    ADS  Article  Google Scholar 

  38. 38

    Snaith, O. N. et al. The dominant epoch of star formation in the Milky Way formed the thick disk. Astrophys. J. Lett. 781, L31 (2014).

    ADS  Article  Google Scholar 

  39. 39

    Licquia, T. C. & Newman, J. A. Improved estimates of the Milky Way’s stellar mass and star formation rate from hierarchical Bayesian meta-analysis. Astrophys. J. 806, 96 (2015).

    ADS  Article  Google Scholar 

  40. 40

    Nataf, D. M. The controversial star-formation history and helium enrichment of the Milky Way bulge. Publ. Astron. Soc. Aust. 33, e023 (2016).

    ADS  Article  Google Scholar 

  41. 41

    Krumholz., M. R., Kruijssen, J. M. D. & Crocker, R. M. A dynamical model for gas flows, star formation and nuclear winds in galactic centres. Mon. Not. R. Astron. Soc. 466, 1213–1233 (2017).

    ADS  Article  Google Scholar 

  42. 42

    Figer, D. F., Rich, R. M., Kim, S. S., Morris, M. & Serabyn, E. An extended star formation history for the galactic center from Hubble Space Telescope NICMOS observations. Astrophys. J. 601, 319–339 (2004).

    ADS  Article  Google Scholar 

  43. 43

    Ruiter, A. J., Belczynski, K. & Fryer, C. Rates and delay times of Type Ia supernovae. Astrophys. J. 699, 2026–2036 (2009).

    ADS  Article  Google Scholar 

  44. 44

    Childress, M. J., Wolf, C. & Zahid, H. J. Ages of Type Ia supernovae over cosmic time. Mon. Not. R. Astron. Soc. 445, 1898–1911 (2014).

    ADS  Article  Google Scholar 

  45. 45

    Foreman-Mackey, D., Hogg, D. W., Lang, D. & Goodman, J. emcee: the MCMC hammer. Publ. Astron. Soc. Pacif. 125, 306 (2013).

    ADS  Article  Google Scholar 

  46. 46

    Holcomb, C., Guillochon, J., De Colle, F. & Ramirez-Ruiz, E. Conditions for successful helium detonations in astrophysical environments. Astrophys. J. 771, 14 (2013).

    ADS  Article  Google Scholar 

  47. 47

    van Kerkwijk, M. H., Chang, P. & Justham, S. Sub-Chandrasekhar white dwarf mergers as the progenitors of Type Ia supernovae. Astrophys. J. Lett. 722, 157–161 (2010).

    ADS  Article  Google Scholar 

  48. 48

    Fink, M. et al. Double-detonation sub-Chandrasekhar supernovae: can minimum helium shell masses detonate the core? Astron. Astrophys. 514, A53 (2010).

    Article  Google Scholar 

  49. 49

    Sim, S. A. et al. Detonations in sub-Chandrasekhar-mass C+O white dwarfs. Astrophys. J. Lett. 714, 52–57 (2010).

    ADS  Article  Google Scholar 

  50. 50

    Sullivan, M. et al. The subluminous and peculiar Type Ia supernova PTF 09dav. Astrophys. J. 732, 118 (2011).

    ADS  Article  Google Scholar 

  51. 51

    Moore, K., Townsley, D. M. & Bildsten, L. The effects of curvature and expansion on helium detonations on white dwarf surfaces. Astrophys. J. 776, 97 (2013).

    ADS  Article  Google Scholar 

  52. 52

    Lodders, K. Solar System abundances and condensation temperatures of the elements. Astrophys. J. 591, 1220–1247 (2003).

    ADS  Article  Google Scholar 

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R.M.C. was the recipient of an Australian Research Council Future Fellowship (FT110100108). Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics through project number CE110001020. D.M.N. is supported by the Allan C. and Dorothy H. Davis Fellowship. The authors thank J. Avila, J. Beacom, N. Bell, G. Bicknell, D. Clayton, K. Freeman, O. Gerhard, J. Hurley, T. Ireland, A. Karakas, M. Kerr, J. Machacek, F. Melia, D. Murtagh, R. O’Leary, R. Pakmor, T. Siegert, P. Tisserand, R. Volkas, A. Wallner, R. Wyse and F. Yuan for very useful discussions. They particularly thank B. Schmidt for pointing out the potential importance of SN1991bg-like SNe to the positron problem.

Author information




All the authors discussed the results and commented on the manuscript. R.M.C. wrote the paper. A.J.R. performed the BPS modelling and provided theoretical input. I.R.S. provided theoretical input, helped with calculating the yields of the helium detonations and contributed to the writing of the paper. F.H.P., A.M. and B.E.T. provided advice about the rates, prevalence and distribution of 91bg in supernova searches. H.B., L.F. and J.J.E. provided advice on the BPS modelling. A.M. and M.W. provided statistical analysis. D.M.N. provided advice about the star formation history of the Galactic bulge and other theoretical input. S.S. provided input on the phenomenology of SN explosions. F.A. provided input on the phenomenology of positron transport and annihilation radiation. All the authors commented on the draft text.

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Correspondence to Roland M. Crocker.

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Crocker, R., Ruiter, A., Seitenzahl, I. et al. Diffuse Galactic antimatter from faint thermonuclear supernovae in old stellar populations. Nat Astron 1, 0135 (2017).

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