We present a measurement of the sky distribution of positronium ( Ps ) annihilation continuum emission obtained with the SPI spectrometer on board ESA ’ s INTEGRAL observatory .
The only sky region from which significant Ps continuum emission is detected is the Galactic bulge .
The Ps continuum emission is circularly symmetric about the Galactic centre , with an extension of about 8 ^ { \circ } FWHM .
Within measurement uncertainties , the sky distribution of the Ps continuum emission is consistent with that found by us for the 511 keV electron-positron annihilation line using SPI .
Assuming that 511 keV line and Ps continuum emission follow the same spatial distribution , we derive a Ps fraction of 0.92 \pm 0.09 .
These results strengthen our conclusions regarding the origin of positrons in our Galaxy based on observations of the 511 keV line .
In particular , they suggest that the main source of Galactic positrons is associated with an old stellar population , such as Type Ia supernovae , classical novae , or low-mass X-ray binaries .
Light dark matter is a possible alternative source of positrons .