PSR J2222?0137

The PSR J2222-0137 binary system is a unique laboratory for testing gravity theories. To fully exploit its potential the tests, we aim to improve measurements of physical parameters: spin, orbital orientation, and post-Keplerian parameters which quantify observed relativistic effects. We present improved analysis archival VLBI data, using coordinate convention in full agreement with that used timing. also obtain much polarimetry FAST. provide an significantly extended timing data taken Effelsberg, Nancay, Lovell Green Bank telescopes. From new estimate position angle ascending node, Omega=189(19) deg, pulsar more conservative uncertainty. FAST particular detection interpulse, yield spin geometry pulsar, inclination axis 84 deg. 1% test general relativity (GR) from Shapiro delay advance rate periastron. Assuming GR self-consistent all effects, mass: 1.831(10) M_sun 1.319(4) companion; total mass, 3.150(14) confirms it as most massive double degenerate known Galaxy. This yields orientation: 85.27(4) indicating close alignment between angular momentum; Omega = 188(6) matching our result. precise value period derivative, 0.251(8)e-12 s s^-1, consistent expected variation Doppler factor plus decay caused by emission gravitational wave (GW) predicted GR. introduces stringent constraint on dipolar GW.