A cloudy region in space, with two bright beams of white and blue light shooting out in either direction.
IN SPACE: In this handout from NASA/ESA, an artist's concept illustrates a quasar, or feeding black hole. NASA's Wide-field Infrared Survey Explorer (WISE) revealed millions of potential black holes in its survey of the sky in 2011. The WISE telescope, which ceased operation is February of 2011 after it ran out of coolant to keep its electronics cool, made the full sky image and was released to the public in March with hopes of astronomers making discoveries. NASA/ESAvia Getty Images

A quasar is an astronomical entity that emits incredibly high levels of electromagnetic radiation (including light). The amount of energy emitted by a quasar dwarfs whole galaxies, making them favorites of astrophysicists and cosmologists who wish to study distant space, as the light from quasars can outshine even the rest of the stars in the distant galaxies that they inhabit. A single quasar can give off more energy than 100 normal galaxies.

Many scientists believe that a quasar is created by matter interacting with the supermassive black holes at the heart of most known galaxies. The matter that collects close to the black hole forms an accretion disk, with gravitational influences that cause a super-heating of the matter up to millions of degrees. The resulting energy is released in the form of jets of radiation that extend millions of light years from the supermassive black hole.

Because of the structure of quasars, they are more common in earlier galaxies that existed in the early universe, before the process consumes the bulk of the dust and gas from region around the supermassive black hole. Since the light now reaching us from distant galaxies was emitted in the distant past when those galaxies were very young, we see quasars in distant galaxies. Closer galaxies, on the other hand, are older and not longer contain quasars.

This is why the observed quasars are so far away from us.

There are over 200,000 known quasars, falling between 600 million and 29 billion light-years away from the Earth. Many quasars are about 1 kiloparsec (or 3.26 lightyears) in width, significantly larger than our entire solar system ... including the Oort Cloud!

History of Quasar Observations

As astronomers began to use radio telescopes in the 1950s, they began detecting points of radio signals that were similar to those seen from stars but contained noticeable differences. These "quasi-stellar" sources of radiation were observed through the 1950s. By 1960, hundreds of these objects had been observed. The distinctive feature of these objects was that though the radio telescopes could detect the radiation signal in the radio wave range, there was no visible object that could be seen along with it.

Attempts to explain what these objects were took a while to develop. Through the 1970s, there was a heated debate about whether these objects were extremely distant from the Earth, or whether they were nearer to the Earth and their apparent redshift was caused by gravitational effects rather than motion from the expansion of space. Models similar to the modern explanation were developed in the 1970s and have since become widely accepted within the scientific community. 

Quasars are part of a class of objects known as active galactic nuclei (AGN), which also include blazars (a sub-type of quasar; see below) and Seyfert galaxies. It is now understood that these are a common part of the earlier life cycle of galaxies.

Also Known As:

The word "quasar" is short for "quasi-stellar radio sources." The name was attributed by Chinese-American astrophysicist Hong-Yee Chiu in 1964. Research since has indicated that they are actually faint emitters of radio waves in comparison to the other forms of energy they emit. They are sometimes also just called "quasi-stellar objects" or "QSO" to include both the "radio-loud" types (about 10% of all quasars) and "radio-quiet" classes.

A quasar with a jet of energy that points directly toward the Earth is called a blazar