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    CALCULATORiQ™
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    Cosmology
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    Dark Matter Laboratory

    Three of the strongest empirical pillars for dark matter, rendered as a live laboratory. Switch between galaxy rotation curves, gravitational lensing, and the bullet cluster to see what the data does, and what a halo of non-baryonic mass changes.

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    Choose a regime and adjust the physics

    8.0 × 10¹¹ M☉
    20 kpc

    Toggle the halo off to recover the Newtonian prediction from visible mass alone. Observed rotation curves of disk galaxies remain flat far beyond the optical edge.

    WHY ROTATION CURVES MATTER

    If only the visible disk produced gravity, orbital velocity should fall like 1 over square root of radius beyond the bulge. It does not. From the 1970s onward, neutral-hydrogen surveys traced flat rotation curves out to tens of kiloparsecs. The most economical fit is an extended halo of pressureless, weakly interacting mass.

    WHY LENSING MATTERS

    Light is bent by the gravitational potential, not by luminous matter directly. The mass map reconstructed from cluster lensing routinely exceeds the visible mass by a factor of five to ten. The geometry of arcs and Einstein rings independently fixes the halo profile.

    WHY THE BULLET CLUSTER MATTERS

    In 1E 0657-56 two clusters collided. The X-ray emitting gas, which carries most of the baryonic mass, was slowed by ram pressure. The lensing mass kept going. The spatial offset between gas and total mass is hard to reconcile with any modified-gravity theory in which gravity tracks baryons.