  Binary systems are ubiquitous and their formation requires two-body
interaction and dissipation. In gaseous media, interactions between two
initially unbound objects could result in gas-assisted binary formation,
induced by a loss of kinetic energy to the ambient gas medium. Here we derive
analytically the criteria for gas-assisted binary capture through gas dynamical
friction dissipation. We validate them with few-body simulations and explore
this process in different gas-rich environments: gas-embedded star-forming
regions (SFR), gas-enriched globular clusters, AGN disks and
protoplanetary-disks. We find that gas-assisted binary capture is highly
efficient in SFRs, potentially providing a main channel for the formation of
binaries. It could also operate under certain conditions in gas-enriched
globular clusters. Thin AGN disks could also provide a fertile ground for
gas-assisted binary capture and in particular the formation of black-hole/other
compact object binaries, the production of gravitational-wave (GW) and other
high-energy transients. Large-scale gaseous disks might be too thick to enable
gas-assisted binary capture and previous estimates of the production of
GW-sources could be overestimated, and sensitive to specific conditions and the
structure of the disks. In protoplanetary-disks, while gas-assisted binary
capture can produce binary KBOs, dynamical friction by small planetsimals is
likely to be more efficient. Overall, we show that gas-assisted binary
formation is robust and can contribute significantly to the binary formation
rate in many environments. In fact, the gas-assisted binary capture rates are
sufficiently high such that they will lead to multicaptures, and the formation
of higher multiplicity systems.
