We present the first results from the SWARMS survey , an ongoing project to identify compact white dwarf ( WD ) binaries in the spectroscopic catalog of the Sloan Digital Sky Survey .
The first object identified by SWARMS , SDSS 1257+5428 , is a single-lined spectroscopic binary in a circular orbit with a period of 4.56 hr and a semiamplitude of 322.7 \pm 6.3 \mathrm { km s ^ { -1 } } .
From the spectrum and photometry , we estimate a WD mass of 0.92 ^ { +0.28 } _ { -0.32 } \mathrm { M _ { \odot } } .
Together with the orbital parameters of the binary , this implies that the unseen companion must be more massive than 1.62 ^ { +0.20 } _ { -0.25 } \mathrm { M _ { \odot } } , and is in all likelihood either a neutron star or a black hole .
At an estimated distance of 48 ^ { +10 } _ { -19 } pc , this would be the closest known stellar remnant of a supernova explosion .