In the Kaluza-Klein (KK) scenario with n large extra dimensions where gravity propagates in the 4+ n dimensional bulk of spacetime while gauge and matter fields are confined to a four dimensional subspace, the light graviton KK modes can be produced in the Sun, red giants and supernovae. We study the energy-loss rates through photon-photon annihilation, electron-positron annihilation, gravi-Compton-Primakoff scattering, gravi-bremsstrahlung and nucleon-nucleon bremsstrahlung, and derive lower limits to the string scale M S . The most stringent lower limit obtained from SN1987A leads to M S >30–130 TeV (2.1–9.3 TeV) for the case of two (three) large extra dimensions.