What are the extremely bright centers of distant galaxies believed to be powered by, due to the presence of a supermassive black hole at the center?

• A. Nebulae
• B. Quasars
• C. Pulsars
• D. Galaxies

Answer: (B)

The main idea is that the brightest centers of distant galaxies come from material falling into a supermassive black hole at the galaxy’s center. As gas and dust spiral in, they heat up and release enormous energy across the spectrum, sometimes so intensely that the core outshines the rest of the galaxy. This blazing center is what we call a quasar when it’s exceptionally bright. Nebulae are just clouds of gas and dust lit by stars, not powered by black hole accretion. Pulsars are rapidly rotating neutron stars emitting beams of radiation, not central engines of galaxies. Galaxies are large systems of stars and gas; the very bright center described here is an active galactic nucleus powered by a supermassive black hole, i.e., a quasar.