Why interstellar bananas would kill more positrons than they produce
My latest publication explores how positron interactions with alkali metal atoms - elements like lithium, sodium and potassium - can constrain the different proposed scenarios for positron production in the Milky Way. This provides further evidence that positron production is a steady-state process, or at least that events producing positrons recur on sub-million year timescales. What's more, this paper can be used to show that if positrons are produced through the beta+ decay of potassium-40, the low ionization potential of the potassium atom makes it an exceptionally good positron annihilation target, even for the lowest energy positrons. In summary, the positrons produced by your bunch of bananas probably aren't going very far.
Don't blame the Fermi Bubbles...
In this paper, published in MNRAS Letters earlier this year, I explore a putative connection between the Galactic outflow that seems to inflate massive gamma-ray bubbles seen by the Fermi satellite (the "Fermi Bubbles") and the annihilation of positrons in the Galactic bulge. We propose that this Galactic outflow 'drags' positrons out of the central region of the Galaxy. However, our detailed model shows that a steady-state outflow cannot reproduce the spectral characteristics of positron annihilation in the Galaxy.
Ancient supernovae can explain the origin of Galactic antimatter?
In this Nature Astronomy article, my collaborators and I suggest that sub-luminous, thermonuclear supernovae associated with old stellar populations could be responsible for producing up to 90% of the positrons we observe annihilating in the Milky Way. This article in Scientific American, by Charles Q. Choi, summarizes our findings. (Paper can also be found on arXiv)