Buro Quasar stands for clarity and strength
with the energy corresponding to many systems combined
The absolute brightness, a measure of the true luminosity, of quasars corresponds to the energy radiated by up to 100 galaxies, making them the brightest objects in the universe. The actual size of a quasar, on the other hand, is much smaller than a single galaxy.
Quasars, after gamma-ray bursts and supernovae, are the brightest and farthest objects we can observe. This is because they are galaxies that have a very bright core. These systems were formed at a time when the universe was very young. They contain a large amount of dust, young stars and gas. Such objects were discovered because they emit very strong radio rays.
With a traditional telescope, quasars are little more than a bright spot. They were given the name 'quasi stellar radio objects' and are classified with the abbreviation QSO. In the center of a quasar is a very strong black hole that absorbs all young stars and gas, releasing a large amount of radiation. This radiation can have as much energy as 100 galaxies. This phenomenon lasts about several billion years until all matter has been absorbed from the system. The radiation that is emitted is perpendicular to the plane of the galaxy. This is shot into space at great speed and is also known as a 'jets' or jet stream. When matter is depleted, the quasar will die out and continue as a normal galaxy. Because of this, astronomers know that many galaxies were probably quasars in the early days of their existence. So in order to observe these, scientists must look into the past, which is to say at very great distances from Earth.
Short but powerful
Some quasars show brightness variations on short time scales, which means they are intrinsically small in size. An object cannot change brightness in less time than it takes light to travel from one place to another. Thus, the size of a quasar that varies on time scales of a few weeks cannot exceed a few weeks of light.
The heart of a quasar is believed to be a supermassive black hole, located in the center of an active galaxy, which attracts matter from its environment. Around the black hole an accretion disc is formed, a flattened, swirling disc of matter, in which matter is constantly slowed down by collisions. The friction heats the material as it approaches the black hole closer and closer, until it eventually falls in. Before the matter falls into the hole, it emits large amounts of radiation. Perpendicular to the plane of the disk, matter is shot into the universe at great speed, forming two so-called 'jets' (jet streams).
Quasars don't just emit visible light: they radiate energy across the entire electromagnetic spectrum. Because of the great distance from Earth and the finite speed of light, we see quasars as they looked billions of years ago, when the Universe was even younger.
The reason that quasars are common in the early Universe and are rare or absent at shorter distances is probably that over time the gas has disappeared from the immediate vicinity of the black hole; the "fuel" for the black hole has run out. To release the energy emitted by an average quasar, a supermassive black hole must absorb at least the equivalent of 10 solar masses per year of matter.