Unit 26
The extreme universe.
Gravity and light at the limit: nebulae, neutron stars, black holes, gravitational waves and lensing.
Before this unit
The unit, lesson by lesson
Lessons
5 lessons · 29 practice questions · about 2 hours
Nebulae
Clouds of gas and dust between the stars: why some glow red, some blue and some are black patches, and how big a bubble a hot star keeps ionised.
Neutron stars and pulsars
What is left of a heavy star that exploded: a ball the width of a city that spins hundreds of times a second and sweeps us like a lighthouse.
Black holes
Gravity not even light escapes: how big the horizon is, how it grows with mass, and why a black hole’s shadow is bigger than its horizon.
Gravitational waves
Two black holes spiral together and merge, sending ripples through space itself: how much mass turns into waves, why a heavy pair “sounds” low, and how tiny the change the detector measures is.
Gravitational lensing
A galaxy bending the light of a distant one behind it into a ring, arcs or a cross: why it happens, how the ring’s size depends on mass, and how it weighs matter no one can see.