The brightest object that we have ever discovered in space is known as a quasar. Quasars are extremely luminous active galactic nuclei located at the centers of distant galaxies. They emit enormous amounts of energy, outshining entire galaxies and even galaxy clusters.
Quasars are powered by supermassive black holes that are actively accreting matter from their surrounding regions. As matter falls into the black hole's gravitational well, it forms an accretion disk, where it heats up and emits intense radiation across the electromagnetic spectrum, including visible light. This radiation can be billions of times brighter than the combined light of all the stars in the host galaxy.
The extreme brightness of quasars allows us to detect them from great distances, even billions of light-years away. Due to the vast distances involved, observing these objects also provides valuable insights into the early universe and the formation and evolution of galaxies.
It's worth noting that quasars are not visible to the naked eye from Earth. Their immense brightness is primarily detected and studied through advanced telescopes and astronomical instruments.