Massive bodies and escape speed Gravity bends the path of light

Rotating black holes

• A rotating black hole (one with angular momentum) has an ergosphere around the outside of the event horizon
• In the ergosphere, space and time themselves are dragged along with the rotation of the black hole

As you fall into to a black hole, you shine a blue flashlight at a friend exterior to the hole, she sees

• blue light
• blue light at first, then turning red
• blue light, then red, then nothing
• nothing

Black holes evaporate

Seeing Black Holes

• Observed properties of black holes
• Gravitational energy
• Rotating black holes
• Eddington luminosity
• Accretion disks
• Jets

Accretion disk

Accretion disks

• Disks form because infalling matter has angular momentum.
• Accretion leads to release of gravitational energy.
• Inner regions of disks rotate very rapidly – near the speed of light.
• The luminosity of a black hole is limited by its mass.