Baryon Acoustic Oscillation (Toy)

What you are seeing: a high-density perturbation in the early universe (photons + baryons + dark matter). Photons drag baryons outward as a pressure wave at $c_s \approx c/\sqrt{3(1+R)}$ . At recombination, the wave freezes at the "sound horizon" $\sim 150$ Mpc, leaving a baryon shell around each density peak.

Figure 1. Sound wave + baryon shell around a perturbation.

R baryon0.60

WHAT TO TRY

Raise R (baryon loading): the sound speed c_s = c/sqrt(3(1+R)) drops, so the pressure wave freezes at a smaller sound horizon. Heavier baryons mean a tighter BAO ring.
Watch the shell form around the central peak: at recombination the photon-baryon wave stalls and leaves baryons piled in a roughly 150 Mpc shell. That fixed scale is the standard ruler.
Track the r_s readout as you tune R: it is the comoving distance the wave traveled before recombination, the quantity galaxy surveys measure to anchor dark energy.