Article

Diffuse Galactic antimatter from faint thermonuclear supernovae in old stellar populations

  • Nature Astronomy 1, Article number: 0135 (2017)
  • doi:10.1038/s41550-017-0135
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Abstract

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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Acknowledgements

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

Affiliations

  1. Research School of Astronomy and Astrophysics, Australian National University, Canberra 2611, Australia.

    • Roland M. Crocker
    • , Ashley J. Ruiter
    • , Ivo R. Seitenzahl
    • , Fiona H. Panther
    • , Anais Möller
    • , David M. Nataf
    •  & Brad E. Tucker
  2. ARC Centre of Excellence for All-Sky Astrophysics (CAASTRO), Canberra 2611, Australia.

    • Ashley J. Ruiter
    • , Ivo R. Seitenzahl
    • , Fiona H. Panther
    • , Anais Möller
    •  & Brad E. Tucker
  3. School of Physical, Environmental and Mathematical Sciences, UNSW Canberra, Australian Defence Force Academy, Canberra 2612, Australia.

    • Ivo R. Seitenzahl
  4. School of Mathematics and Physics, Queen’s University, University Road, Belfast BT7 1NN, UK.

    • Stuart Sim
  5. School of Mathematics and Physics, University of Queensland, Brisbane 4072, Australia.

    • Holger Baumgardt
  6. Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA.

    • David M. Nataf
  7. Center for Astrophysical Sciences, The Johns Hopkins University, Baltimore, Maryland 21218, USA.

    • David M. Nataf
  8. Mathematical Sciences Institute, Australian National University, Canberra 2601, Australia.

    • Lilia Ferrario
  9. Department of Physics, University of Auckland, Auckland 1010, New Zealand.

    • J. J. Eldridge
  10. Department of Physics, University of Adelaide, Adelaide 5005, Australia.

    • Martin White
  11. Dublin Institute for Advanced Studies, 10 Burlington Road, Dublin 4, D04 C932, Ireland.

    • Felix Aharonian
  12. Max-Planck-Institut für Kernphsik, Saupfercheckweg 1, 69117 Heidelberg, Germany.

    • Felix Aharonian

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Contributions

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.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Roland M. Crocker.

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