The ultra-diffuse galaxy NGC1052-DF2 has a very low velocity dispersion , indicating that it has little or no dark matter .
Here we report the discovery of a second galaxy in this class , residing in the same group .
NGC1052-DF4 closely resembles NGC1052-DF2 in terms of its size , surface brightness , and morphology ; has a similar distance of D _ { sbf } = 19.9 \pm 2.8 Mpc ; and also has a population of luminous globular clusters extending out to \geq 7 kpc from the center of the galaxy .
Accurate radial velocities of the diffuse galaxy light and seven of the globular clusters were obtained with the Low Resolution Imaging Spectrograph on the Keck I telescope .
The velocity of the diffuse light is identical to the median velocity of the clusters , v _ { sys } = \langle v _ { gc } \rangle = 1445 km s ^ { -1 } , and close to the central velocity of the NGC1052 group .
The rms spread of the globular cluster velocities is very small at \sigma _ { obs } = 5.8 km s ^ { -1 } .
Taking observational uncertainties into account we determine an intrinsic velocity dispersion of \sigma _ { intr } = 4.2 ^ { +4.4 } _ { -2.2 } km s ^ { -1 } , consistent with the expected value from the stars alone ( \sigma _ { stars } \approx 7 km s ^ { -1 } ) and lower than expected from a standard NFW halo ( \sigma _ { halo } \sim 30 km s ^ { -1 } ) .
We conclude that NGC1052-DF2 is not an isolated case but that a class of such objects exists .
The origin of these large , faint galaxies with an excess of luminous globular clusters and an apparent lack of dark matter is , at present , not understood .