Of the seven known double neutron stars ( DNS ) with precisely measure masses in the Milky Way that will merge within a Hubble time , all but one has a mass ratio , q , close to unity .
Recently , precise measurements of three post-Keplerian parameters in the DNS J1913 + 1102 constrain this system to have a significantly non-unity mass ratio of 0.78 \pm 0.03 .
One may be tempted to conclude that approximately one out of seven ( 14 % ) DNS mergers detected by gravitational wave observatories will have mass ratios significantly different from unity .
However J1913 + 1102 has a relatively long merger time of 470 Myr .
We show that when merger times and observational biases are taken into account , the population of Galactic DNSs imply that \simeq 98 \% of all merging DNSs will have q > 0.9 .
We then apply two separate fitting formulas informed by 3D hydrodynamic simulations of DNS mergers to our results on Galactic DNS masses , finding that either \simeq 0.004 { M _ { \odot } } or \simeq 0.010 { M _ { \odot } } of material will be ejected at merger , depending on which formula is used .
These ejecta masses have implications for both the peak bolometric luminosities of electromagnetic counterparts ( which we find to be \sim 10 ^ { 41 } erg s ^ { -1 } ) as well as the r -process enrichment of the Milky Way .