Since the 1963 discovery of quasi-stellar objects, popularly called quasars or QSOs, astronomers have been debating the origin and distance of these giant, energetic objects. Today, most astronomers agree on many aspects of quasars, but there are a few dissenters.
Since the 1980s, there have been numerous definitions of quasars-consider this one, from Wikipedia, written by astronomer Fulvio Melia: "There is now a scientific consensus that a quasar is a compact region 10-10,000 Schwarzschild radii across surrounding the central supermassive black hole of a galaxy, powered by its accretion disc."
Part of the service of this column is to translate scientific Gobbledygook language into English. Let's attempt it:
Quasars appear as bright points of light in the night sky, much like stars. But they aren't stars-they are far bigger and far more energetic. Astronomers distinguish quasars from stars and galaxies by their extreme "redshift".
Redshifting of the spectrum of visible light occurs when objects move away from the observer-so quasar light is shifted toward the red end of the spectrum. This visible effect is the lightwave equivalent of the Doppler Shift in soundwaves, the effect of an approaching and receding train as heard by the human ear. (In the light spectrum, objects moving toward an observer are blueshifted.)
In the case of quasars, their red lines are shifted so much that they are unlike any other stellar objects moving away from us. This observation tells most observers that quasars are the fastest moving objects and the most distant from us.
The nearest quasar is 800 million light years away, which means all quasars are very ancient things that no longer exist in the modern universe.
Here's an aside about "scientific consensus" regarding quasars: A few astronomers, notably Halton Arp of the Max-Planck Institute, believe QSOs are far closer to Earth than is commonly believed. Arp says they are being ejected from some galactic nuclei, perhaps spewing from "white holes". If Arp's disputed observations are ever proven to be correct, his quasar theory-if logically extended-would damage the thesis underlying the Big Bang theory and how we understand redshifts. But that's another discussion. Be that as it may, conventional wisdom says that the quasars we observe, by looking back in space and time, no longer exist.