AGN

AGN, standing for Active Galactic Nucleus, refers to the intensely luminous central region of some galaxies, powered by a supermassive black hole (SMBH) that actively accretes surrounding material. This accretion process, where matter spirals inwards, forms a hot accretion disk, releasing tremendous energy across the electromagnetic spectrum, from radio waves to gamma rays. The observed properties of an AGN are influenced by factors such as the SMBH's mass, the accretion rate, the viewing angle, and the surrounding environment, including obscuring material such as gas and dust. AGNs are crucial in understanding galaxy evolution, SMBH growth, and the universe's high-energy phenomena.

AGN meaning with examples

• Astronomers observed a sudden brightening in the center of galaxy NGC 4151, suggesting a change in its AGN's activity. This pointed to a possible increase in the material accreting onto the supermassive black hole. The data, collected across various wavelengths, is expected to yield valuable insight into the nature of the AGN and the mechanisms driving its outbursts, improving understanding of AGN behavior.
• The Hubble Space Telescope captured stunning images of powerful jets emanating from the AGN of M87, demonstrating its active energy output. This discovery validated the theory of how matter gets pulled into black holes. Scientists are studying the characteristics of the jet's plasma to further understand the mechanisms that drive AGN feedback, shaping galaxy morphology.
• Quasars, among the most luminous objects in the universe, are a type of AGN thought to be in the early stages of galaxy formation. Observing the quasars allows scientists to peer back in time to the universe when the first galaxies were evolving. Researchers used various telescopes to analyze the spectral fingerprints of these AGNs, to assess the chemical composition of the intergalactic medium surrounding quasars.
• The presence of a highly energetic AGN can significantly impact the surrounding galaxy through a process called 'AGN feedback'. Through its radiation and jets, it can heat and expel gas, which can stop or decrease star formation, therefore altering the shape of the host galaxy. Such AGN interactions are fundamental in explaining the observed correlations between the mass of the central SMBH and the properties of the host galaxy.