We report the discovery during the Parkes Multibeam Pulsar Survey of PSR J1756 - 2251 , a 28.5 ms pulsar in a relativistic binary system .
Subsequent timing observations showed the pulsar to have an orbital period of 7.67 hrs and an eccentricity of 0.18 .
They also revealed a significant advance of periastron , 2.585 \pm 0.002 deg .
yr ^ { -1 } .
Assuming this is entirely due to general relativity implies a total system mass ( pulsar plus companion ) of 2.574 \pm 0.003 M _ { \odot } .
This mass and the significant orbital eccentricity suggest that this is a double neutron star system .
Measurement of the gravitational redshift , \gamma , and an evaluation of the Shapiro delay shape , s , indicate a low companion mass of < 1.25 M _ { \odot } .
The expected coalescence time due to emission of gravitational waves is only \sim 1.7 Gyr substantially less than a Hubble time .
We note an apparent correlation between spin period and eccentricity for normally evolving double neutron star systems .