We propose a question that why no late type M and much later type N white dwarfs (WDs) with surface temperatures less than 3000 K have ever been observed? On the basis of proton decay catalyzed by magnetic monopoles(MMs), we have presented four new energy-source models associated with MMs to discuss the cooling of WDs by some observations from seven red giant stars with LAMOST. It is found that the number of MMs captured by a WD can reach the maximum value of [Formula: see text] when the MMs flux [Formula: see text]. The good agreement of our luminosities calculated for WDs with the observations shows that our models are rational due to the Rubakov Callan (RC) effect by MMs. It is concluded that the energy source of WDs is the proton decay catalyzed by MMs. We obtain a new limit of the MMs flux of [Formula: see text] for WDs when the number density of nucleons [Formula: see text] and asteroseismic correction factor [Formula: see text] due to the RC effect by MMs.

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The influence of strong electron screening (SES) on electron capture (EC) plays a key role in supernovae explosions. We investigate the influence of SES on EC of iron group nuclei by the linear response theory model (LRTM) and the plasma sphere theory model (PSTM). The corrections of the Q-value, the electron chemical potential, electron energy, the Coulomb wave correction factor, and nuclear blinding energy by SES are considered. The screening rates even decrease by [Formula: see text] and [Formula: see text] by PSTM and LRTM, respectively. We compare our screening results with those of Fuller et al. (FFN), Aufderheide et al. (AUFD), Nabi et al. (NKK), and Martinez-Pinedo et al. (MLD). Our screening rates can be lowered about by [Formula: see text], 2, and 1 orders of magnitude than those of AUFD (FFN), NKK, and MLD, respectively.

Based on the magnetic monopoles(MMs) catalytic nuclear decay (RC effect), we propose five new models to discuss the limit of the MMs' flux and the cooling energy resources of the white dwarfs (WDs) by some observations from 13 RGB stars. We find that the number of MMs captured can reach the maximum value of $9.1223\times10^{24}$ when $m=10^{17}, n_B=5.99\times10^{31}, \phi=7.59\times10^{-26}$. The good agreement of our luminosities calculated for WDs with the observations shows that our model is rational due to RC effect by MMs. We obtain the new limit of the MMs' flux of $\xi=\phi\langle\sigma_m v_{\rm{T}}\rangle_{-28}\leq 9.0935\times10^{-13}$, and $\xi\leq 4.9950\times10^{-13}$ at $n_B=5.99\times10^{31}$ when $m=10^{15}, beta=9.4868\times10^{-3}$, and $m=10^{17}, \beta=10^{-3}$, respectively. Our results show that the RC effect could be preventing white dwarfs from cooling down into a stellar graveyard by keeping them hot. Our results will also provide a new idea for further research on the upper limit of MMs' flow.