MOCCA-SURVEY Database -- I. Tidal disruption events of white dwarfs in globular clusters and young massive clusters.

We investigate more than 1000 star cluster models (about half of all the cluster models in MOCCA-Survey Database I), and obtain the local rate density of white dwarf (WD) tidal disruption events (TDEs) in globular clusters (GCs) and young massive clusters (YMCs). We find that WD TDEs in a star cluster happen 1000 times more efficiently than predicted previously. We take into account WD TDEs in GCs, YMCs, and dwarf galaxies, and obtain the total WD TDE rate density in the local universe as $\sim 5.0 \times 10^2~{\rm yr}^{-1}~{\rm Gpc}^{-3}$, 90 % of which happens in GCs. The total WD TDE rate density is 50 times larger than estimated before. Our results show that thermonuclear explosions induced by WD TDEs can be observed at a rate of $\lesssim 550~{\rm yr}^{-1}$ by the next generation optical surveys, such as the Large Synoptic Survey Telescope. We also find that massive WDs are preferentially disrupted due to mass segregation, and that 20 % of exploding WDs have $\gtrsim 1.0 M_\odot$ despite of small population of such WDs. Such explosions can be as luminous and long as type Ia supernovae (SNe Ia), in contrast to previous arguments that such explosions are observed as more rapid and faint transients than SNe Ia due to their small radioactive mass ($\lesssim 0.1 M_\odot$) and ejecta mass ($\lesssim 0.6 M_\odot$).