Finding the Invisible
Begin with measurements, not silhouettes: motion, mass, hot gas, light, and the first careful intuition for an event horizon.
Evidence for an Unseen Object
Learn why a missing point of light is not evidence, then build a candidate from repeated motion, an unseen companion, a mass constraint, and follow-up radiation.
Free- 01If a Black Hole Is Invisible, How Do We Know It Is There?
What must move, glow, bend, or arrive before an unseen object becomes a black-hole candidate?
Free · 36 min - 02How Do We Weigh an Unseen Companion?
How can a visible star's orbit constrain the mass hiding beside it?
Free · 36 min - 03Why Can Falling Gas Produce X-rays?
Why does gas outside a black hole become an energetic messenger?
Free · 36 min - 04Black Hole or Another Compact Remnant?
Which measurements separate a black-hole candidate from a white dwarf, neutron star, or incomplete model?
Free · 36 min
From Strong Gravity to an Event Horizon
Build only the minimum spacetime intuition needed to understand a horizon, while reserving relativity derivations for the future deep course.
Member- 05From Escape Speed to a No-Return Boundary
Where does the familiar escape-speed analogy help, and where does it fail?
Member · 36 min - 06Why Is an Event Horizon Not a Solid Surface?
What kind of boundary can be crossed without striking a wall?
Member · 36 min - 07What Does Curved Spacetime Mean Here?
How can paths and clocks change without imagining gravity as an invisible rope?
Member · 36 min - 08What Happens to Light and Clocks in Strong Gravity?
Which effects are measured, which are predicted, and whose viewpoint matters?
Member · 36 min