short for "quasi-stellar radio sources," are among the brightest
and most energetic objects in the universe. They appear as point-like sources of light,
resembling stars, hence the term "quasi-stellar."
Quasars are typically found at extreme distances
from Earth and are powered by supermassive black holes at the centers of galaxies.
Here are some key characteristics of quasars:
Supermassive Black Holes: At the heart of every quasar lies a supermassive black hole
with millions to billions of times the mass of the Sun. These black holes are surrounded by
an accretion disk—a swirling mass of gas, dust, and other matter.
Emission of Radiation: As material falls into the black hole's gravitational pull, it releases
an enormous amount of energy in the form of light and other electromagnetic radiation.
This emission can span the entire electromagnetic spectrum, from radio waves to gamma rays.
Luminosity: Quasars are incredibly luminous, often outshining entire galaxies.
Some quasars can emit thousands of times more energy than our entire Milky Way galaxy.
Redshift: Most quasars are found at vast distances from Earth, and their light is redshifted
due to the expansion of the universe. This redshift provides valuable information
about the age and distance of quasars.
Evolution: Quasars are thought to be more common in the early universe, billions of years ago,
during a period known as the "quasar epoch." As galaxies evolve, their central black holes
may consume much of the available material, leading to a decrease in quasar activity.
Jet Formation: Some quasars exhibit powerful jets of particles and radiation streaming away from
their centers at nearly the speed of light. These jets can span millions of light-years and play a
significant role in shaping the surrounding interstellar medium and galaxy formation.
Quasars are essential objects for studying the early universe, galaxy evolution, and the physics of extreme environments such as those near supermassive black holes. They offer valuable insights into the processes that drive the growth and behavior of galaxies over cosmic time.