ACTIVE GALACTIC NUCLEUS
What is an Active Galactic Nucleus?
An Active Galactic Nucleus as the name suggests is a small region at the centre of a galaxy which is very luminous, it is even brighter than the remaining part of the galaxy. These nuclei present in the centre of the galaxies are termed as Active Galactic Nuclei or AGN in short and the galaxies containing those nuclei are called "active galaxies". Such excess non-steller emission has been observed in the radio, infrared, microwave, optical, ultraviolet, X-rays and gamma rays wavebands which indicates that this luminosity is not produced by stars.
How an AGN is formed?
We know that every galaxies have a supermassive black holes at their centers; some billion of times the mass of the sun. When material gets too close, it forms an accretion disk around the black hole. It heats up to millions of degrees, blasting out an enormous amount of radiation. The magnetic environment around the black hole form twin jets of materials which flow into space for millions of light-years and this is called an AGN, an active galactic nucleus.
The interesting thing is that AGN look different depending on how we see them. If we see them and the jets at an angle of 90 degrees from our line of sight then we call it a "Radio Galaxy". If we see them at an angle then it is called a 'Quasar'. An if we are starring right down the jet then it is known as a 'Blazar'.
Does the Milky Way have an AGN?
The supermassive black holes are not always consuming materials and when they run out of material or food, the jet run out of power and shut down until something else gets too close, the whole system starts again. The Milky Way galaxy has a supermassive black hole at it's center, and it's all out of food. It doesn't have an active galactic nucleus.
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