Galaxies, part 2: Crash Course Astronomy #39

When 3C273 was first observed through optical telescopes, how did it appear?

• As a bright, distant galaxy.

• As an ordinary star.

• As a luminous powerhouse emitting radio waves.

• As a galaxy blasting out gamma rays.

What is the primary mechanism by which supermassive black holes power active galaxies?

• Nuclear fusion within the black hole's core.

• The direct emission of light from the black hole itself.

• Friction and heating of matter in an accretion disk as it falls into the black hole.

• The collision of stars within the galactic core.

What is the current state of the supermassive black hole at the center of the Milky Way galaxy?

• It is actively feeding and blasting out high-energy light.

• It is quiescent, meaning it is not actively feeding.

• It is about to collide with another black hole.

• It is emitting powerful jets of matter and energy.

What is the predicted outcome when the Milky Way and Andromeda galaxies eventually collide and merge?

• They will pass by each other without interacting.

• They will form two smaller, irregular galaxies.

• They will merge to form one much larger elliptical galaxy.

• They will both be destroyed by their central black holes.

What is a typical characteristic of a galaxy cluster?

• It contains only a few dozen stars.

• It is typically a few tens of millions of light-years across and can contain thousands of galaxies.

• It is a single, isolated galaxy.

• It is primarily composed of gas and dust, with very few stars.

Which of the following represents the largest known structure in the universe, composed of multiple galaxy clusters?

• Local Group

• Galaxy Cluster

• Supercluster

• Nebula

Approximately how many galaxies are estimated to exist in the observable universe?

• Millions

• Billions

• Trillions

• Quadrillions