  The origin of Galactic cosmic rays (CRs) is unknown even though they have
traditionally been connected to supernovae based on energetic arguments. In the
past decades, Galactic black holes in X-ray binaries (BHXBs) have been proposed
as candidate sources of CRs, which revises the CR paradigm. BHXBs launch two
relativistic jets during their outbursts, but recent observations suggested
that these jets may be launched even during quiescence. A0620-00 is a
well-studied object that shows indications of jet emission. We study the
simultaneous radio-to-X-ray spectrum of this source that was detected while the
source was in quiescence to better constrain the jet dynamics. Because most
BHXBs spend their lifetimes in quiescence (qBHXBs), we used the jet dynamics of
A0620-00 to study a population of $10^5$ such sources distributed throughout
the Galactic disc, and a further 104 sources that are located in the boxy bulge
around the Galactic centre. While the contribution to the CR spectrum is
suppressed, we find that the cumulative intrinsic emission of qBHXBs from both
the boxy bulge and from the Galactic disc adds to the diffuse emission that
various facilities detected from radio to TeV gamma rays. We examined the
contribution of qBHXBs to the Galactic diffuse emission and investigated the
possibility of SKA, INTEGRAL, and CTAO to detect individual sources in the
future. Finally, we compare the predicted neutrino flux to the recently
presented Galactic diffuse neutrino emission by IceCube.
