Recently , [ van Dokkum et al .
( 2018 ) van Dokkum , Danieli , Cohen , Merritt , Romanowsky , Abraham , Brodie , Conroy , Lokhorst , Mowla , O ’ Sullivan , & Zhang ] have presented an important discovery of an ultra-diffuse galaxy , NGC1052-DF2 , with a dark matter content significantly less than predicted from its stellar mass alone .
The analysis relies on measured radial velocities of 10 Globular Clusters ( GCs ) , of estimated individual masses of a few \times 10 ^ { 6 } M _ { \odot } .
This is about 1 \% of the inferred mass of NGC1052-DF2 of 2 \times 10 ^ { 8 } M _ { \odot } within a half-light radius , R _ { \mathrm { e } } = 2.2 \mathrm { kpc } .
The large relative mass and the old age of these objects imply that they might be susceptible to orbital decay by dynamical friction .
Using analytic estimates and N-body simulations of an isolated system matching the inferred mass profile of NGC1052-DF2 , we show that orbits of the most massive GCs should already have decayed on a time scale of a few Gyrs .
These findings should help in constraining mass profile and formation scenarios of NGC1052-DF2 .