RSAA Colloquia / Seminars / Feast-of-Facts: Friday, 07 December 2018, 14:00-15:00; CSO Common Room

Fiona Panther

"Positron annihilation in the Milky Way: Searching for a source of Galactic antimatter (End-of-thesis colloquium)"

For more than 50 years, the rate and distribution of positron (anti-electron) annihilation in the Milky Way has puzzled astronomers. Positrons with low (~MeV) initial energies are predominantly produced by beta+ unstable radioactive elements, however, the observed rate of positron annihilation in the Milky Way far exceeds the predicted rate of positron production by ’conventional sources’ such as core-collapse and Type Ia supernovae. Moreover, the observed distribution of positron annihilation in the Milky Way appears to trace the older stellar populations of the Galaxy (the Galactic bulge and a thick, truncated disk), while radioactive material is predominantly synthesised in the thin disk of the Galaxy. Over the past four years of my PhD candidature, I have constrained scenarios for positron injection and transport in energetic outflows of the Milky Way, investigated positron annihilation sites in the Milky Way beyond annihilation with electrons bound to hydrogen and helium atoms, as well as investigating in detail the possibility that positrons are born in the ejecta of subluminous thermonuclear supernovae that concentrate in old stellar populations. I will present highlights of this theoretically-focussed work in my talk, along with emphasis on the implications of this work beyond high-energy astrophysics. Please join my collaborators and I for an antimatter-themed cake in the CSO common room following the talk.