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A SCIENCE EXPEDITION / 3 CHAPTERS / 8 STOPS

The Boundary of No Return

What can we know about a place that cannot send light back?

Travel from the Milky Way’s central black hole to the evidence outside its horizon. Compare scale, motion and bent light before confronting the limits of an interior model.

90–150 minutes, across several visits. No deadline; each chapter is a natural place to pause.

Conceptual artwork illustrating a black hole and its surrounding light
AI concept artwork, not a telescope observation.

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Chapter 1 · Find the boundary
  1. 01

    Field guide

    Separate horizon, shadow and light

    Ready to explore

    Find the distinction between the event horizon, surrounding light and the shadow. Which features are model-dependent?

    Explore stop 1 →
  2. 02

    3D Atlas

    Visit our galaxy’s central black hole

    Ready to explore

    Explore the illustrated Sagittarius A* scene. Distinguish its scale comparisons and artistic choices from evidence about the actual object.

    Explore stop 2 →
Chapter 2 · Put a scale on the darkness
  1. 03

    Interactive lab

    Change the mass, compare the horizon

    Ready to explore

    Use the Black-hole horizons comparison. Double a mass and compare the radius. Remember that this teaching calculation assumes a non-spinning black hole.

    Explore stop 3 →
  2. 04

    Printable activity

    Check the horizon arithmetic

    Ready to explore

    Work through More Mass. A Larger Horizon. Explain why a horizon-size calculation is not a measurement of the interior.

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  3. 05

    Investigation

    Follow a star around the unseen

    Ready to explore

    Trace how orbital measurements could constrain spin. What observations and modelling would still be needed?

    Explore stop 5 →
Chapter 3 · Ask what the evidence can reach
  1. 06

    Evidence File

    Audit the spin claim

    Ready to explore

    Separate the measured orbit from a prospective spin measurement. Which claims belong to future observations?

    Explore stop 6 →
  2. 07

    Interactive lab

    Bend light in a teaching model

    Ready to explore

    Change an alignment and inspect image positions and delays. This simplified thin-lens model illustrates lensing; it does not reconstruct a black-hole interior.

    Explore stop 7 →
  3. 08

    Investigation

    Reach the limits of the model

    Ready to explore

    Compare a mathematical interior with a physically established conclusion. Why do stability and predictability matter before interpreting the Cauchy horizon?

    Explore stop 8 →
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