Galaxies and the Cosmic Web

Chapter 6

Galaxies and the Cosmic Web

This chapter brings into the game BPT Part 3.14 (Galaxies: the Wells and the Stars Around Them) and the parts of BPT Part 3.12 (Ripples, Spin, and the Whirling Disks) that make a disk, with the swarm of data that BPT Part 2.9 (Gas, Stars, and the Stellar Road to the Null Well) wraps round every forming cluster of stars. Part 3.14 says what a galaxy is: a halo gathered round its well, its stars the ones that well pulls hardest, with satellites sinking toward the deepest heart. It says how its type is read (the blue cloud of star-forming disks and the red sequence of quiet spheroids), how a disk raises its own arms (Shear Rate, Epicyclic Frequency, Arm Number, Arm Pitch Angle), how wide it settles (Disk Size) and how fast it turns (Disk Turn Rate), and it makes a prediction the game can score: wells are born where the Proto Wells stood (Site Lift). Part 3.12 gives the order of events: a random field of ripples grows a tangled web, tidal torques spin the clumps, and cooling gas keeps its spin and settles into a whirling disk.

The arc is this. In the theory, matter condensed at the Physical Nova falls into the web, gathers round the wells and the sites, forms stars, and settles into galaxies of a few kinds, each turning at a rate set by when it formed, fed by cold streams along the filaments. In the game, the matter is a field of drawn bodies moving under their own gravity on the torus (Chapter 5); nothing in it is labeled a galaxy. Every four Pulses the game reads the galaxies out of that field: it gives each body to the well that pulls it hardest, finds the satellites, reads each galaxy's type from its young blue stars, measures its rotation curve and asks the book's laws for its arms and pitch, sizes it by its halo's spin, and turns it by the Disk Turn Rate. What the player watches, in the 3D view of the torus, is that reading drawn: from the big bang on, star-forming spirals with blue-white arms on warm cores, gold lenticulars, orange ellipticals and patchy blue irregulars gather round their wells, each star wheeling on its own orbit, streams of blue stars falling in along the filaments toward the largest, and the web itself glowing on the torus's skin as clusters where filaments cross and dim voids between.

A note on the field. The field is 4·2^Lm cells a side, Lm the model level: 6 on a desktop (256 × 256 cells), 4 on a phone (64 × 64). Every size in this chapter is in cells of that field, every time in flips, and every mass in the drawn units of matter.js unless it says Suns.