2026ApJ...997..162Z

Supersoft X-ray sources (SSSs) are characterized by persistent thermonuclear burning on the surfaces of white dwarfs (WDs). The standard model requires high mass-transfer rates of ∼10^–7M_⊙ yr^–1 from massive companions, presenting a theoretical impediment to the observed short-period SSSs, whose orbital periods imply low-mass donors theoretically incapable of sustaining such accretion. To resolve this paradox, we propose and demonstrate through detailed simulations that irradiative feedback following a classical nova eruption provides a natural formation channel. Through detailed binary evolution simulations with MESA, we reveal that sustained WD irradiation-initially from the outburst and subsequently from accretion luminosity-triggers significant and stable expansion of the low-mass companion. This, in turn, drives mass-transfer rates into the stable hydrogen-burning regime and sustains it beyond 10⁴ yr after the initiation of hydrogen burning. This mechanism robustly explains the observed population of short-period SSSs. Moreover, when the irradiation-driven mass-transfer rate drops below the stable accretion rate, it may lead to the rapid accumulation of sufficient material on shorter timescales to trigger a recurrent nova outburst instead of SSS, thereby also offering an explanation for the origin of short-period recurrent novae.