This artist’s conception of a quasar shows a thick doughnut-shaped torus surrounding a small bright inner region of hot swirling gas. The inner region is about the size of our solar system and is called an accretion disk. At the very center is a supermassive black hole that steadily consumes, or accretes, the surrounding gas. As illustrated here, some quasars have strong jets beaming away perpendicularly to the disk of swirling matter. While the outer torus can sometimes block much of the light emitted by the interior, when the interior light is visible, it can be a hundred thousand times as bright as our Milky Way Galaxy!

(NASA/CXC/M.Weiss)

An ordinary star emits radiation primarily at ultraviolet, visible, and infrared wavelengths, in varying proportions that are governed by the star’s surface temperature. Composed of many stars, ordinary galaxies, too, emit most strongly in these wavelength regions. But the object illustrated here, called a quasar, is outrageously different: It emits strongly over an immense range of wavelengths from radio to X-ray.

The name quasar refers to one of the most fantastic types of objects in all of astronomy. At a quasar’s core is a supermassive black hole that can be a billion times more massive than our Sun! Hot gas around this black hole can give off a tremendous amount of visible light—enough to shine with a luminosity ten thousand times more than a typical galaxy.

As in this illustration, some quasars even have strong jets. Unlike young stars that form smaller and slower-speed jets, matter in quasar jets travels near the speed of light and can shoot well beyond the galaxy that hosts the quasar. Galaxies that hold a quasar—always at the galaxy’s center—are called active galaxies. Untangling the mysterious properties of quasars has been in process for more than half a century and is still a major topic of research today. Physicist George Gamow captured the intriguing nature of quasars in his 1964 revised lullaby: