Location from remembrance-of-earths-past by
The unremarkable nearby star Yun Tianming bought for Cheng Xin out of his cancer money — later confirmed by AA's gravitational-lensing work to host two habitable worlds, eventually wrapped in a black domain to hide it forever.
DX3906 is the trilogy's only happy ending, sized to fit two people. Yun Tianming and AA live out their lives on its inner world after the black-domain enclosure cuts the system off from the Dark Forest. Cheng Xin and Guan Yifan visit, briefly, before time dilation pulls them into a different fate. The star itself becomes the closest thing humanity has to a grave marker.
A small yellow main-sequence star with two terrestrial planets, the inner one Earth-like with deep oceans and stable continents, the outer cooler and ice-rimmed. From its inner world, the star looks much like the Sun. After the black-domain installation, the entire system is wrapped in a sphere of slowed light that hides it from anything outside.