Hot Disk at a Galaxy Center

In the picture

1. 1Dark central circle: the supermassive black hole at the galaxy’s core
2. 2White-hot inner ring: gas heated to millions of degrees as it spirals inward
3. 3Orange outer band: cooler gas still orbiting in the accretion disk
4. 4Pale blue-white glow: X-ray light from the hottest inner gas

Examples

• A hidden electric heater can be found by the red glow of its hot coil.
• A doctor uses X-rays to see a bone even though the X-rays themselves are invisible.

Quiz: Hot Disk at a Galaxy Center (Age 16)

1. 1

   How do astronomers detect supermassive black holes at the centers of galaxies?

   • By the X-rays emitted by their hot accretion disks
   • By the cold gas orbiting far outside the galaxy
   • By the dark shadow of the black hole itself
2. 2

   What happens to gas pulled toward a supermassive black hole at a galaxy’s center?

   • It escapes the galaxy without changing temperature
   • It remains cold and completely invisible to astronomers
   • It forms a swirling accretion disk and becomes hot enough to glow in X-rays
3. 3

   Where are supermassive black holes usually found?

   • At the centers of most large galaxies
   • In the empty space between galaxies
   • Inside the cores of stars

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.