We report the discovery of an ultra-faint Milky Way satellite galaxy in the constellation of Pegasus .
The concentration of stars was detected by applying our overdensity detection algorithm to the SDSS-DR 10 and confirmed with deeper photometry from the Dark Energy Camera at the 4-m Blanco telescope .
Fitting model isochrones indicates that this object , Pegasus III , features an old and metal-poor stellar population ( [ Fe/H ] \sim - 2.1 ) at a heliocentric distance of 205 \pm 20 kpc .
The new stellar system has an estimated half-light radius of r _ { h } = 78 ^ { +30 } _ { -24 } pc and a total luminosity of M _ { V } \sim - 4.1 \pm 0.5 that places it into the domain of dwarf galaxies on the size–luminosity plane .
Pegasus III is spatially close to the MW satellite Pisces II .
It is possible that the two might be physically associated , similar to the Leo IV and Leo V pair .
Pegasus III is also well aligned with the Vast Polar Structure , which suggests a possible physical association .