Quasar

Quasi-stellar radio sources (quasars) are the most distant cosmic objects observed by astronomers. Although not visible to the naked eye, quasars are also among the most energetic of cosmic phenomena.

Although some quasars may be physically smaller in size than our own solar system, some quasars are calculated to be brighter than hundreds of galaxies combined. Quasars and active galaxies appear to be related phenomena, each associated with massive rotating black holes in their central region. As a type of active galaxy, the enormous energy output of quasars can be explained using the theory of general relativity.

The great distance of quasars means that the light observed coming from them was produced when the Universe was very young. Because of the finite speed of light, large cosmic distances translate to looking back in time. The observation of quasars at large distances and of their nearby scarcity argues that quasars were much more common in the early Universe. Correspondingly, quasars may also represent the earliest stages of galactic evolution. This change in the Universe over time (e.g., specifically the rate of quasar formation) contradicted steady-state cosmological models that relied on a Universe that was the same in all directions (when averaged over a large span of space) and at all times. Along with the discovery of ubiquitous cosmic background radiation, the discovery of quasars and tilted the cosmological argument in favor of Big Bang based cosmological models.