AGN is a three-letter word which phonetically is spelled /æɡn/. It is considered an acronym for Active Galactic Nuclei. It refers to a compact region at the center of a galaxy that has an unusually high luminosity compared to the remaining parts of the galaxy. AGNs are powered by accretion, where matter falls into a supermassive black hole. They emit extremely high-energy radiation and are useful in studying the evolution of galaxies. The spelling of AGN is derived from the first letter of each word in the phrase "Active Galactic Nuclei".
AGN, or Active Galactic Nucleus, refers to the compact region at the center of a galaxy that displays intense emission across various wavelengths of the electromagnetic spectrum. Active Galactic Nuclei are known for their high luminosity, which often exceeds the combined brightness of the stars in the rest of the galaxy. AGNs typically exhibit a very compact size, often just a few parsecs in diameter, and are believed to host a supermassive black hole at their core.
The emission from AGNs arises from a combination of different processes, including accretion of matter onto the supermassive black hole and the subsequent release of large amounts of energy, as well as intense magnetic fields and high-speed jets of particles expelled from the central region. These phenomena result in the emission of radiation across a broad range of wavelengths, from radio waves to X-rays and even gamma rays.
The study of AGNs is crucial to understanding the evolution of galaxies, as they play a significant role in regulating the growth of their host galaxies through their powerful radiation and outflows. AGNs are classified into different types based on their observed properties, such as Seyfert galaxies, quasars, and blazars. Research on AGNs encompasses a wide range of observational and theoretical studies, aiming to unravel the complex physical processes occurring within these energetic cosmic powerhouses.