The extreme outer Galaxy ( EOG ) , the region with a Galactic radius of more than 18 kpc , is known to have very low metallicity , about one-tenth that of the solar neighborhood .
We obtained deep near-infrared ( NIR ) images of two very young ( \sim 0.5 Myr ) star-forming clusters that are one of the most distant embedded clusters in the EOG .
We find that in both clusters the fraction of stars with NIR excess , which originates from the circumstellar dust disk at radii of \leq 0.1 AU , is significantly lower than those in the solar neighborhood .
Our results suggest that most stars forming in the low-metallicity environment experience disk dispersal at an earlier stage ( < 1 Myr ) than those forming in the solar metallicity environment ( as much as \sim 5–6 Myr ) .
Such rapid disk dispersal may make the formation of planets difficult , and the shorter disk lifetime with lower metallicity could contribute to the strong metallicity dependence of the well-known “ planet-metallicity correlation ” , which states the probability of a star hosting a planet increases steeply with stellar metallicity .
The reason for the rapid disk dispersal could be increase of the mass accretion rate and/or the effective far-ultraviolet photoevaporation due to the low extinction ; however , another unknown mechanism for the EOG environment could be contributing significantly .