By: Emily Wang
Quasars are powerful monsters that live in the core of galaxies. They are powered by supermassive black holes, surrounded by a disk of gas and dust called the accretion disk. The disk is then heated to millions of degrees by friction and then emits a lot of radiation. Quasars live very very far away from us. As a result, what we see in outer space is from a billion, if not more, years ago. The most distant quasar known is around 13 billion light-years away. Quasars are a type of AGN, (active galactic nucleus), which is a term for a galaxy with a very bright center.
An accretion disk is formed from diffuse material (such as gas, dust, or plasma) that is in motion around a main central body, such as a star, a black hole, or a planet. The material in the disk spirals inward toward the central body because it loses energy and angular momentum due to friction, viscosity, or other forces. As the material falls inward, it gets heated up by the gravitational and frictional forces. The shape and size of the accretion disk depend on the balance between the gravitational, rotational, and pressure forces. If the pressure is low, the disk will be thin and flat. If the pressure is high, the disk will be thick and torus-like.
Quasars are very rare; there are only about 10,000 quasars in the observable universe, compared to hundreds of billions of galaxies. That is because quasars are very short-lived. They only last for a few hundred million years, which is a blink of an eye in cosmic terms. This is because they consume their fuel very quickly and eventually run out of gas. Quasars also come In several different forms, such as radio-loud, radio-quiet, broad absorption-line, and weak emission line quasars. These types reflect different properties of the quasars in the spectrum, the amount of dust obscuration, the orientation of the jet, and the brightness of the emission lines.
Astronomers find quasars using different methods and instruments, depending on the properties of the quasar and the distance of the quasar. Some of the methods are:
● Using radio telescopes to detect the strong radio emission from some quasars, especially those with jets of plasma that are launched perpendicular to the accretion disk around the black hole.
● Using optical telescopes to observe the visible light from quasars, which can appear as faint blue stars in the sky. The spectra of quasars can reveal their redshifts, which indicate how fast they are moving away from us and how far they are.
● Using X-ray telescopes to observe the high-energy radiation from quasars, which can be produced by the hot gas in the accretion disk or by the interaction of the jets with the surrounding medium.
● Using infrared telescopes to observe the dust emission from quasars, which can be heated by the radiation from the accretion disk or by star formation in the host galaxy.