What Is A Quasar?

What is a quasar?

An extremely luminous active galactic nucleus. According to NASA, quasars are the most luminous type of active galaxy. They emit light across the entire electromagnetic spectrum, produce powerful particle jets, and can radiate thousands of times the energy emitted by a galaxy like the Milky Way. Despite their galaxy-scale luminosity, quasars are physically small (light hours or days across), so they appear as point sources like stars in most telescopes. The name quasar is short for quasi-stellar radio source, a label coined in the 1960s when they were first identified.

What powers quasars?

Supermassive black holes consuming matter. At the center of each quasar is a supermassive black hole millions to billions of times the mass of the Sun. Surrounding the black hole is an accretion disk of gas and dust spiraling inward. As this material falls toward the event horizon, it heats up to extreme temperatures and emits enormous amounts of radiation. The process is the most efficient form of energy production known in nature, converting up to 40% of matter's rest mass into energy. Many quasars also launch jets of particles moving at nearly the speed of light from their poles.

How far away are quasars?

Mostly very far. Over 1 million quasars have been identified. The nearest, Markarian 231, is about 600 million light years away. Most are much more distant. The farthest known quasars are about 13 billion light years away, meaning we see them as they appeared less than a billion years after the Big Bang. The most distant confirmed quasar (as of 2024) is ULAS J1342+0928, from when the universe was only 690 million years old. Distant quasars give us views of the early universe.

Are quasars still active?

Most stopped long ago. Quasars are most common at high redshifts (distant past), peaking when the universe was 2 to 3 billion years old. As galaxies aged and central black holes ran out of nearby material, quasar activity declined. The supermassive black hole at the center of the Milky Way (Sagittarius A*) is essentially dormant today, but probably went through quasar phases earlier. Many galaxies that hosted quasars in their youth are now ordinary galaxies. Active quasars in the local universe are rare.