What Are Quasars (QUAsi-Stellar Radio Source)?Quasars are very energetic and distant galaxy with an active galactic nucleus. They are the most luminous objects in the universe.
This article is part of a series of articles. Please use the links below to navigate between the articles.
- Constellation Guide and Associated Mythology
- What are Asteroids, Meteors and Comets?
- What Are Binary Stars and Double Stars
- What are Variable Stars and How to Observe Them
- What are Supernova and Supernovae?
- What Nebula and Nebulae, What are the Types of Nebula?
- What Are Black Holes? Black Holes Explained - From Birth to Death
- What Are Quasars (QUAsi-Stellar Radio Source)?
- Pulsars - Natures Lighthouses Key to Astronomy
- What is a Neutron Star and What Are They Made Of?
- What Are Gamma Ray Bursts and Where Do They Come From?
- What is the Kuiper Belt and Kuiper Belt Objects?
- What is an Exoplanet? How Can We Detect Exoplanets?
- What is a galaxy? What Types of Galaxy Are There? Where Do They Come From?
- The Messier Catalogue of Objects To Observe
- The Caldwell Catalogue
- 25 Stunning Sights Every Astronomer Should See
Quasars, also known as QUAsi-Stellar Radio Sources, are not just distant galaxies with an active galactic nucleus. They are the most luminous objects in the universe, emitting energy that is truly awe-inspiring.
Quasars, those enigmatic high redshift sources of electromagnetic energy, were not always understood. They were first identified as point-like sources, similar to stars, rather than extended sources like galaxies, adding to their mystery.
There was a time when the nature of these objects was a subject of intense scientific debate. As recently as the early 1980s, there was no clear consensus. However, through rigorous research and observation, a scientific consensus emerged, revealing that a quasar is a compact region in the centre of a massive galaxy, surrounding its central supermassive black hole. Its size, a staggering 10-10,000 times the Schwarzschild radius of the black hole, is powered by an accretion disc around the black hole.
In this artist's concept, a growing black hole can be seen at the centre of a faraway galaxy. Using NASA's Spitzer and Chandra space telescope, astronomers discovered swarms of similar quasars hiding in dusty galaxies in the distant universe. The quasar is the orange object at the centre of the large, irregular-shaped galaxy. It consists of a dusty, doughnut-shaped cloud of gas and dust that feeds a central supermassive black hole. As the black hole feeds, the gas and dust heat up and spray out X-rays, as illustrated by the white rays. Beyond the quasar, stars can be seen forming in clumps throughout the galaxy. Other similar galaxies hosting quasars are visible in the background.
Quasars show a very high redshift, which is an effect of the expansion of the universe between the quasar and the Earth. They are the most luminous, powerful, and energetic objects known. When combined with Hubble's law, the redshift implies that the quasars are very distant, thus from much earlier in the universe's history. The most luminous quasars radiate at a rate that can exceed the output of average galaxies, equivalent to one trillion (1012) Suns.
More than 200,000 quasars have been discovered, with the majority identified through the Sloan Digital Sky Survey. These quasars, with their redshifts between 0.056 and 7.085. Applying Hubble's law to these redshifts, they are located between 600 million and 28.85 billion light-years away. The vast distances to the farthest quasars, coupled with the finite velocity of light, give us a glimpse into the very early universe, underscoring the significance of their study.
