Quasars – What is a Quasar?

Quasars are the brightest objects in the universe. The supermassive black hole that powers quasars is fed by enormous amounts of gas. The extraordinarily bright centers of active galaxies in the far-off universe are known as quasars. They are an extreme variation of what astronomers refer to as Active Galactic Nuclei (AGN).

A Quasar is sometimes referred to as a QSO, short for Quasi-Stellar Object since the nature of these objects is entirely unknown.

When a galaxy’s center supermassive black hole is actively eating matter, the galaxy is said to be active. Due to the enormous rate at which matter falls into the black hole, it is unable to enter at one time and instead creates a spiraling accretion disk in the form of a queue.

Massive clouds of matter descend into the disk, their core regions orbiting faster than their outer regions as they get closer to the black hole (much like planets orbiting faster than those farther away).

The clouds are twisted by the shear force created, and as they orbit the black hole at speeds varying from 10% to over 80% of light’s speed, they collide with one another. The disk heats up to millions of degrees due to friction from the rapidly moving gas clouds, which causes it to glow brightly.

Additionally, a portion of the disk’s material is directed away from the black hole by an incredibly bright and magnetically collimated jet. The core of the active galaxy shines so brightly that it can be seen from a great distance across the universe.

In the galaxy merger scenario, giant clouds of molecular gas in colliding galaxies change their direction of travel due to the disturbance induced by their different gravitational fields, falling in the direction of the black hole.

Even though quasars are extremely bright, their power source is small in comparison to the host galaxy in which they are located. Because quasars are so small, light can move quickly across the accretion disk from one side to the other, allowing astronomers to observe fluctuations in their light. 

Light can travel across quasars in as little as a few days, depending on their size. This would translate to a diameter of fewer than 1,000 astronomical units in this instance. This corresponds to the size of the accretion disk surrounding the black hole. The accretion disk grows in size with increasing black hole mass. The largest might be many light-years across.

Quasars Explained:

Quasars, these distant beacons outshining entire galaxies, continue to amaze astronomers. Their immense luminosity and the extreme environments they reside in offer a glimpse into the universe’s most energetic processes. Here’s a deeper exploration of these celestial powerhouses:

The Fueling Frenzy: 

The supermassive black hole at the heart of a quasar is a gluttonous entity. It devours surrounding gas and dust at an astonishing rate, sometimes exceeding the mass of our Sun every year. This infalling material forms a swirling accretion disk, where immense friction heats the gas to unimaginable temperatures, exceeding millions of degrees. This intense heat is the primary source of a quasar’s brilliance.

Cosmic Jets: 

Nature’s Particle Accelerators: Not all the infalling material gets consumed by the black hole. Some get channeled away along the poles in the form of powerful jets. These jets, collimated by strong magnetic fields, can travel vast distances at speeds approaching the speed of light. The interaction between these jets and the surrounding interstellar medium can further contribute to the quasar’s overall luminosity.

A Tapestry of Change: 

Quasar activity isn’t a constant state. It’s believed to be an episodic phenomenon, with a quasar flaring brightly during periods of intense feeding and fading over time as the available fuel dwindles. Studying these variations in luminosity helps astronomers understand the growth and evolution of supermassive black holes.

Cosmic Detectives: 

Using Quasars as Probes: The immense distances to quasars, often billions of light-years away, make them valuable tools for studying the early universe. As their light travels to us, it interacts with the intergalactic medium, absorbing specific wavelengths.

By analyzing the spectrum of this light, astronomers can probe the composition of the universe at these vast distances, providing insights into the cosmic environment during its formative stages.

The Mystery of Quasar Formation: 

While the fueling mechanism of quasars is well understood, the exact conditions that trigger quasar activity remain somewhat elusive. Galaxy mergers, where the gravitational interaction between colliding galaxies funnels gas toward the central black hole, might be one possible explanation. Further research into the environments where quasars reside will shed light on the initial conditions necessary for these powerful objects to emerge.

The closest, brightest quasar is called 3C 273.

3C 273 Quasar:

In the Virgo constellation, 3C 273 is a quasar at the heart of a massive elliptical galaxy. With an apparent visual magnitude of 12.9, it is the visually brightest quasar in the sky as viewed from Earth and the first quasar to be discovered.

This object is located at a distance of 749 megaparsecs, or 2.4 billion light years. Its center supermassive black hole has a mass that is roughly 886 million times greater than that of the Sun.

The brightness of 3C 272 is 2.5 x 1040 watts, or 25 trillion times that of our sun. Quasars can be seen Between 10 and 100,000 times brighter than the entire Milky Way galaxy.

Difference between Black Holes with Quasars and Black Holes without Quasars:

Black Holes with Quasars Vs. Black Holes without Quasars

FeatureBlack Holes with QuasarsBlack Holes without Quasars
NicknameActive Galactic Nuclei (AGN)Inactive Black Holes
Activity LevelExtremely active; accreting a large amount of matter, releasing tremendous energyRelatively inactive; may have minimal or no ongoing accretion
Accretion DiskPossesses a massive, swirling accretion disk of gas and dust fueling the black holeMay or may not have a significant accretion disk
EmissionsEmit bright light across the electromagnetic spectrum (radio waves, X-rays, gamma rays)Emit little to no radiation, except for potential faint X-ray emissions if an accretion disk exists
JetsOften generate powerful jets of particles traveling near the speed of lightMay not produce jets
Influence on SurroundingsDramatically influence a large region around them due to intense energy outputLess pronounced influence on their surroundings
DiscoveryPrimarily identified by their bright light emissionsDetected indirectly by their gravitational influence on surrounding matter (stars, gas) or through gravitational wave observations


Their intense energy output and the presence of supermassive black holes at their core continue to challenge our understanding of the universe. Further study of quasars promises to unveil more secrets about the formation and evolution of galaxies, the nature of black holes, and the extreme physics that governs these distant and fascinating objects.

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