Have you ever spotted a quasar in the night sky? Probably not. Even using a good, tripod-mounted telescope from a vantage safe from significant light pollution, they are notoriously difficult to identify. It’s more likely that your gaze would pass over a quasar without noticing or recognizing it – unless you knew exactly where to look.

That’s because, from Earth, quasars are among the faintest sources of light in the sky. In fact, when these objects were first noticed, scientists believed they were somehow related to stars and named them quasi-stellar radio sources, or quasars.

In this image of a very distant quasar powered by a black hole with a mass 2 billion times that of the sun, the quasar appears as a faint red dot close to the center. Image credit: ESO/UKIDSS/SDSS

Quasars Are a Special Class

So, other than having a really cool-sounding name, what is particularly interesting about quasars? Well, studying them with instruments other than optical telescopes, astronomers have learned that they are not stars but a special class of extra-galactic objects. Quasars emit light across a broad spectrum from radio waves to X-rays, which has allowed scientists to date them and make determinations about their behavior and function.

Quasars are bright – dazzlingly, spectacularly, extraordinarily bright. In fact, their luminosity is unequalled in the heavens. They shine brighter than the combined light produced by all the other stars in the galaxies where they are located.

Deep in the heart of space, a billion or so light years from Earth, a quasar collects matter in an enormous rotating disc and feeds energy into a supermassive black hole in this artist’s depiction. Some of this matter is shot into space with astounding force, blasting out with a searing brightness greater than all the other stars in its galaxy combined. From Earth we see only a faint light from the quasar’s propulsive energy.

But if they are so luminous, why do they appear so infinitesimally dim from Earth, even when viewed through strong optical telescopes? That’s because all of them are so confoundingly far away. The nearest quasar yet discovered is 780 million light years from us. But that’s nothing compared to the oldest quasar discovered, which is a mind-blowing 13 billion light years distant, making it one of the oldest objects in the Universe.

Quasars and Supermassive Black Holes

Knowing their age, what can we say about the role of quasars in the Universe, and their function? Among the more intriguing facts is that they are not present in every galaxy, but only one quasar can be found in each of the galaxies where they do exist – and they appear to serve a purpose.

As it happens, quasars are always located in close proximity to supermassive black holes and operate in tandem with them. Moreover, each quasar serves as an accretion disk for its nearby black hole. It rips stars apart and gathers matter, dust, and gas, accelerating mass nearly to the speed of light. The quasar then feeds the particles into the black hole while simultaneously blasting enormous bursts of energy into space in two directions exactly 180 degrees apart.

A quasar, part of a system for feeding matter into a supermassive black hole, pulls matter into it in this artist’s rendering.

The existence of quasars may be an important signpost in the early stages of galaxy formation.

What is the Function of a Quasar?

The light they emit is just a byproduct of the action of quasars. Feeding supermassive black holes a constant stream of super-accelerated, super-heated particle energy is what they do. Understanding this nourishing function leads scientists to speculate that the existence of the mysterious objects may be an important signpost in the early stages of galaxy formation.

Since older galaxies such as the Milky Way lack quasars, investigators suspect that the quasars are relatively short-lived phenomena. Their lifespan appears to be between 10 and 100 million years, while galaxies typically have a life expectancy of 10 billion years or more. Therefore, the “quasar phase” may actually be a stage in the development of younger galaxies when large amounts of dust and gas fall into the supermassive black holes at their hearts.

Seeing a Quasar

All these extremely energetic and destructive processes are intriguing. Naturally, scientists would love to see some visual confirmation of how quasars operate and interact with their companion black holes. But such observations will be difficult to achieve.

This image shows a rare view of four quasars, indicated by white arrows, found within 700,000 light years of each other, in an ancient nebula. The bright galactic nuclei are embedded in a giant nebula of cool, dense gas visible in the image as a blue haze. This finding is so rare that the astronomers who discovered it have named it the “Jackpot Nebula.” The nebula is 10 billion light years from Earth. Image credit: Hennawi & Arrigoni-Battaia, Max Planck Institute for Astronomy

Given the incredible distances that exist between Earth and even the nearest quasars, and considering the current state of our technology, studying them directly is presently an unreachable goal. Although enough is known about the activity of quasars for artists to create imaginative renderings, observing them directly will have to await advances in technology and methodology by future generations. Quasars are in no hurry to give up their secrets.