The physics under the sim

We began with the 119,626 stars that astronomers have measured. The rest of the Milky Way, 111 billion stars from a published model of our galaxy, is generated by the same science, and it is arriving next. The model: 1.11 x 10^11 stars, 2.2 x 10^10 brown dwarfs, 8.4 x 10^8 neutron stars and 8.7 x 10^7 black holes, in a thin disk and a thick disk, a bar and bulge at 28 degrees after Sormani 2022 and Portail 2017, a nuclear disk and cluster with 3.4 million stars in its densest cube, and an Einasto halo, with spiral arms after Reid 2019, the warp after Chen 2019 and dust after Drimmel and Spergel 2001. The Sun sits 8,275 parsecs from the centre (GRAVITY 2021) and 20.8 parsecs above the midplane (Bennett and Bovy 2019).

The rule is that the count is the true population, never a budget: no cap removes an object, and there is no height ceiling. The galaxy fills in around the real stars, not over them: each cell draws its true count, subtracts the catalogue stars already there, and generates the rest as the stars Earth would not have catalogued. The model runs in C++ in the engine and agrees with the reference simulation to one part in a billion; the first whole-galaxy view draws 143,165 stars from 30 kiloparsecs out.

Gas and ice giants come in 75 subtypes across five classes. Their bands are stirred through a wind field built for each planet over forty steps: zonal jets after Ingersoll 2004 with zones anticyclonic and belts cyclonic, Von Karman vortex streets, Saturn's hexagon as a polar wave of order six, and Juno-style polar cyclones. Ammonia ice sits at about 0.7 bar over ammonium hydrosulfide at about 2 bar; limb darkening follows Minnaert under a Henyey-Greenstein haze, and the terminator fades as it does in Cassini's frames. Hot giants lock one face to their star where Gladman 1996 says they must. The C++ matches the Python on 264 golden vectors, and on approach the texel reaches 0.21 kilometres on a Jupiter.

Rings take Saturn's optical depths from Cassini occultations, C ring to A ring with the Cassini Division and the Encke and Keeler gaps, at 8.4 kilometres a texel, and sit inside the icy Roche limit: 687 bodies are ringed, and hot giants never. Rocky worlds from orbit are judged against Artemis photographs: maria at albedo 0.075, highlands at 0.14, maria covering 16.8 percent of the sphere against the Moon's 16, and a crater size-frequency slope of minus 1.99 and minus 2.01 against a target of minus two.

One engine unit is 2,000 kilometres; an astronomical unit is 74,798.94 of them. With the ship pinned at the origin and doubles carrying about 16 significant digits, precision is a metre at Neptune and under a millimetre at Pluto in a system frame, and a test in the build proves it. Orbits use J2000 elements and a Kepler solve that agrees with the original simulation within 0.8 millimetres across nine bodies. Sol has 37 bodies with true heliocentric positions.

The orrery plans a real Earth-to-Mars Hohmann transfer: burns of 2.94 and 2.65 kilometres per second, 259 days, a 44 degree phase angle, a 780-day synodic period. Its overlays draw the melt line, Hill spheres, Eggleton Roche lobes, magnetopause scaling, binary barycentres, exact Lagrange points and burn-and-flip times. The atmospheric scout flies on NASA's published F-16 wind-tunnel tables (NASA TP-1538), and the radiation model in the ship uses NIST constants and the NCRP 132 hazard ladder and agrees with every measured case within a factor of two.