A stream of particles jetting from a quasar

Quasars

Mysterious objects emitting radio waves were first identified in 1963 by radio astronomers who called them quasi-stellar radio sources, or quasars. Their origin was debated for a long time, but quasars are now thought to be extremely bright discs of matter swirling around supermassive black holes at the centres of distant galaxies.

Quasars are often so bright that they drown out any light from the galaxies surrounding them, giving them a star-like appearance from our perspective on Earth.

Image: A 100,000 light-year-long stream of particles jets from a quasar (credit: NASA/JPL-Caltech/Yale Univ.)

Watch and listen to clips from past programmes TV clips [6]

A stream of particles jetting from a quasar

Introduction

Astronomers find mysterious objects emitting radio waves.

About Quasars

Quasars (/ˈkweɪzɑr/) or quasi-stellar radio sources are the most energetic and distant members of a class of objects called active galactic nuclei (AGN). Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that appeared to be similar to stars, rather than extended sources similar to galaxies. Their spectra contain very broad emission lines, unlike any known from stars, hence the name "quasi-stellar". Their luminosity can be 100 times greater than the Milky Way.

While the nature of these objects was controversial until the early 1980s, there is now a scientific consensus that a quasar is a compact region in the center of a massive galaxy, that surrounds its central supermassive black hole. Its size is 10–10,000 times the Schwarzschild radius of the black hole. The energy emitted by a quasar derives from mass falling onto the accretion disc around the black hole.

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