  For over a century, the identification of high-energy cosmic ray (CR) sources
remains an open question. For Galactic CRs with energy up to $10^{15}$ eV,
supernova remnants (SNRs) have traditionally been thought the main candidate
source. However, recent TeV gamma-ray observations have questioned the SNR
paradigm. Propagating CRs are deflected by the Galactic magnetic field, hence,
gamma-rays and neutrinos produced via inelastic hadronic interactions are the
only means for unveiling the CR sources. In this work, we study the gamma-ray
and neutrino emission produced by CRs accelerated inside Galactic jets of
stellar-mass black holes in X-ray binaries (BHXBs). We calculate the intrinsic
neutrino emission of two prototypical BHXBs, Cygnus X-1 and GX 339-4, for which
we have high-quality, quasi-simultaneous multiwavelength spectra. Based on
these prototypical sources, we discuss the likelihood of the 35 known Galactic
BHXBs to be efficient CR accelerators. Moreover, we estimate the potential
contribution to the CR spectrum of a viable population of BHXBs that reside in
the Galactic plane. When these BHXBs go into outburst, they may accelerate
particles up to 100s of TeV that contribute to the diffuse gamma-ray and
neutrino spectra while propagating in the Galactic medium. Using HERMES, an
open-source code that calculates the hadronic processes along the line of
sight, we discuss the contribution of BHXBs to the diffuse gamma-ray and
neutrino fluxes, and compare these to their intrinsic gamma-ray and neutrino
emissions. Finally, we discuss the contribution of BHXBs to the observed
spectrum of Galactic CRs.
