What produces the Galaxy's 511 keV positron annihilation line? · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
What produces the Galaxy's 511 keV positron annihilation line?
Plain · changed
Revision 1: About 5e43 positrons per second annihilate in the Milky Way, mostly in the central bulge, and no known source class explains both the rate and the bulge-heavy pattern.
Revision 2: About $5 \times 10^{43}$ positrons per second annihilate in the Milky Way, mostly in the central bulge, and no known source class explains both the rate and the bulge-heavy pattern.
Precise · changed · core
Revision 1: Explain the $511\,\mathrm{keV}$ line (annihilation rate $\sim 5e43\,\mathrm{positrons}/\mathrm{s}$, bulge-to-disk luminosity ratio $\sim 1$) with positrons injected below a few MeV (required by in-flight annihilation limits). Candidates: beta-plus decay of $\mathrm{Al}-26$, $\mathrm{Ti}-44$ and $\mathrm{Co}-56$ from supernovae and novae, microquasars and low-mass X-ray binaries, past activity of Sgr A*, MeV-mass dark matter. Answer: a source mixture reproducing rate, morphology and spectrum, including positron transport.
Revision 2: Explain the $511\,\mathrm{keV}$ line (annihilation rate $\sim 5 \times 10^{43}\,\mathrm{positrons}/\mathrm{s}$, bulge-to-disk luminosity ratio $\sim 1$) with positrons injected below a few MeV (required by in-flight annihilation limits). Candidates: beta-plus decay of $\mathrm{Al}-26$, $\mathrm{Ti}-44$ and $\mathrm{Co}-56$ from supernovae and novae, microquasars and low-mass X-ray binaries, past activity of Sgr A*, MeV-mass dark matter. Answer: a source mixture reproducing rate, morphology and spectrum, including positron transport.
Settled by
High-resolution imaging and spectroscopy of the line, resolving point sources or a profile that singles out one class.
Kind
phenomenon
Answer type
identification
References
(empty)
Literature status
open
Status note
The COSI MeV mission, planned for launch in 2027, will map the line with better angular and energy resolution.
Posed since
(empty)

Decisions