Quasars Explained: The Brightest Objects in the Universe Are Supermassive Black Holes Eating a Solar System Every Year

In 1963, an astronomer named Maarten Schmidt stared at a spectrum printout for a very long time. Then he went pale.

What he was looking at appeared to be a faint blue star. Routine sky survey. Nothing special. Except the spectral lines were shifted so far toward red that the math pointed to something 2 billion light-years away — and blazing brighter than 2 trillion suns.

It wasn't a star. It was something nobody had a name for yet.

They called it a quasi-stellar object. A quasar. And sixty years later, it remains one of the most violent, extreme things the universe has ever made.

How bright is a quasar, really?

The word "bright" doesn't cover it. The most luminous quasar ever discovered — J0529-4351, confirmed in 2024 — shines at roughly 500 trillion times the luminosity of our Sun. It is consuming approximately 370 solar masses of material every single year. That's roughly one entire Sun, swallowed, every day.

Our galaxy has roughly 300 billion stars. A typical quasar outshines every single one of them — combined — by about 100 times. And it produces all that energy from a region smaller than our solar system. Not smaller than our galaxy. Smaller than the distance from the Sun to Neptune.

What actually powers a quasar?

At the center of almost every large galaxy sits a supermassive black hole. Ours is called Sagittarius A* — 4 million times the mass of the Sun. Mostly quiet. Barely eating.

In the early universe, these black holes weren't quiet. They were surrounded by vast clouds of gas and dust — raw material left over from a cosmos still figuring out what it wanted to be. Gas fell toward the black hole in a spiraling disk called an accretion disk, and the friction heated it to tens of millions of degrees. That heat produces light simultaneously across every wavelength: X-rays, ultraviolet, visible light, infrared, radio. All of it blasting outward at once.

Some quasars also fire relativistic jets — twin beams of plasma traveling at nearly the speed of light, shooting perpendicular to the accretion disk, stretching for millions of light-years in both directions. Some jets are longer than the distance between us and the Andromeda Galaxy.

How did we discover quasars?

In the 1950s, radio telescopes were mapping strange signals from the sky that appeared to come from faint blue points of light. Astronomers called them "radio stars" and assumed they were nearby. They were wrong by about 2 billion light-years.

When Schmidt cracked the spectral code of 3C 273 in 1963, the redshift told an impossible story: this "star" was receding as if it were at cosmological distances. The numbers meant it had to be emitting energy no known stellar process could explain through fusion alone.

It took another decade to reach consensus: these were supermassive black holes, actively gorging. The resistance was real — the physics seemed too extreme to accept. But the observations kept coming in, and they all pointed the same way.

Are quasars still active today?

Here's the eerie part. The most extreme quasars you read about aren't happening now. They happened billions of years ago, when the universe was young and swimming in raw material.

When you observe a quasar 10 billion light-years away, you're seeing it as it was 10 billion years ago. The light took that long to reach you. Some of those quasars have been dormant for most of cosmic history. You're watching a historical event, not a live one.

Quasars were common when the universe was between 1 and 3 billion years old — the era when supermassive black holes were growing fastest and the supply of gas hadn't yet been blown away by the quasar's own ferocious output. Today, most galactic cores are quiet. The food ran out. The monsters are sleeping.

Is the Milky Way a dead quasar?

Almost certainly yes. Sagittarius A*, our galactic black hole, masses 4 million solar masses. A black hole that size didn't just appear — it ate its way there over billions of years.

Current models suggest the Milky Way had an active quasar phase roughly 8 to 12 billion years ago. At peak output, our galactic core would have outshone every star in the sky — if Earth had existed to watch it. It hadn't. The solar system is only 4.6 billion years old, born into a galaxy whose wildest days were already over.

What ended it? The quasar itself. The radiation and jets blew away the surrounding gas — the food supply — starving the engine. Sagittarius A* still flickers with brief X-ray flares when stray matter drifts close enough. But the era of blazing output is long past.

If you want to know what the young Milky Way looked like from outside: point a telescope at a distant quasar. That's the view.

What's a blazar — and why does it matter?

Some quasars happen to be oriented so that one of their relativistic jets is aimed almost directly at Earth. These are called blazars. You're looking straight down the barrel.

Blazars are the most energetic persistent sources of radiation in the observable universe. Particles in their jets have been detected arriving at Earth with individual energies that dwarf anything produced by our most powerful accelerators. During a blazar flare, energy output can increase a hundredfold over just a few days.

None of the known blazars are close enough to matter. The nearest is hundreds of millions of light-years away. But the physics is so extreme that astrophysicists still don't fully understand how the jets form, why they sometimes shut off, or what accelerates particles to those energies in the first place.

Can you see a quasar without a professional telescope?

3C 273 — the first confirmed quasar and the nearest at about 2.4 billion light-years — is just barely reachable through a backyard telescope under dark skies. It appears as a faint 12th-magnitude blue point in the constellation Virgo.

When you look at it, the light entering your eye left its source when complex multicellular life was first appearing on Earth. The Cambrian explosion — the moment animals began growing eyes, shells, and bodies — happened roughly 540 million years ago. That light was already 1.86 billion years into its journey toward you. The animals that evolved eyes had no idea.

There is a version of astronomy that is purely about equations and energy densities. And then there is this version: you look at a faint blue smudge through a backyard telescope and understand that you are watching a black hole consume a solar system's worth of matter — from 2.4 billion years in its past — and the photons completing that journey land on your retina in the dark.

That's what quasars are. The universe at its most extreme, still reaching us.

Track objects overhead right now on the SkyLens live tracker, or explore more space science stories on the SkyLens blog.