Our Galaxy hosts the annihilation

Our Galaxy hosts the annihilation of a few 10^43 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 ∼0.03M ⊙ of the positron emitter 44-Ti, can simultaneously explain the strength and morphology of the Galactic positron annihilation signal and the Solar System abundance of the 44-Ti decay product 44-Ca. 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.

https://www.nature.com/articles/s41550-017-0135.epdf?referrer_access_token=pVDIL6sZQwyKJNLdmR26ydRgN0jAjWel9jnR3ZoTv0NsQ6DPIuGo0Hl8A1hHbwL-9_LAk-6u-C4bfocizScITnLuUS-T3wW9PBtBZIq6o_iZSwTIl5Xgaqs9bfpbbsUeWbmrvCQX11Nza1QWgaQWmNReelhkDo-tqYi1QIkqbuxQ8Xdk4RHy1ZMG80BZWGR2M0QxtOsZVAbpqdd86kQxPgJpE0_SjQxW8IC00eWG2cvUwl9GoCsQn3flcaswNpd1UzXxkrnZCw1JzgFvjSKWhDzuiiTxhkCz8JWOcw7yQJU=&tracking_referrer=www.space.com

 

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