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Changing Look AGN

**Changing Look Active Galactic Nuclei (CLAGN)** are a type of **Active Galactic Nuclei (AGN)** that exhibit a significant change in their **spectral energy distribution (SED)** over time, often transitioning from a **radio-loud** to a **radio-quiet** state or vice versa. ## Overview Active Galactic Nuclei (AGN) are incredibly luminous objects at the centers of galaxies, powered by supermassive black holes (SMBHs) actively accreting material. These objects are characterized by their intense emission across the entire electromagnetic spectrum, from radio waves to gamma rays. Changing Look Active Galactic Nuclei (CLAGN) are a subset of AGN that display a remarkable transformation in their spectral energy distribution (SED), often accompanied by changes in their **optical**, **ultraviolet (UV)**, **X-ray**, and **radio** emission. This phenomenon has sparked significant interest in the astrophysical community, as it may provide insights into the complex processes governing the growth and evolution of SMBHs. The study of CLAGN has been facilitated by the advent of advanced telescopes and spectrographs, which have enabled astronomers to monitor the SED of these objects over extended periods. Observations have revealed that CLAGN can undergo significant changes in their emission properties, often in response to variations in the accretion rate or the presence of **relativistic jets**. These changes can be accompanied by dramatic shifts in the object's **luminosity**, **color**, and **polarization**, making CLAGN fascinating objects for study. ## History/Background The concept of CLAGN emerged in the 1990s, as astronomers began to recognize that some AGN exhibited unusual variability in their SED. Early studies focused on the **optical** and **UV** properties of these objects, which were found to change over timescales of months to years. The development of more sensitive telescopes and spectrographs has since enabled astronomers to study CLAGN in greater detail, revealing the complex interplay between accretion, jet activity, and radiation. ## Key Information * **Definition**: CLAGN are AGN that exhibit a significant change in their SED over time, often transitioning from a radio-loud to a radio-quiet state or vice versa. * **Characteristics**: CLAGN are typically found in galaxies with **supermassive black holes** (SMBHs) with masses ranging from 10^6 to 10^9 solar masses. * **Variability**: CLAGN can exhibit dramatic changes in their emission properties, including shifts in luminosity, color, and polarization. * **Accretion**: Changes in the accretion rate are thought to be a key driver of CLAGN variability, with variations in the SMBH's spin and magnetic field also playing a role. * **Relativistic jets**: CLAGN often exhibit relativistic jets, which can interact with the surrounding interstellar medium, producing **synchrotron radiation** and **inverse Compton scattering**. ## Significance The study of CLAGN has significant implications for our understanding of AGN and SMBH growth. By monitoring the SED of these objects over time, astronomers can gain insights into the complex processes governing the growth and evolution of SMBHs. CLAGN may also provide a unique window into the physics of relativistic jets and the interaction between jets and the surrounding interstellar medium. INFOBOX: - Name: Changing Look Active Galactic Nuclei (CLAGN) - Type: Active Galactic Nuclei (AGN) - Date: 1990s (concept emergence) - Location: Galaxies with supermassive black holes (SMBHs) - Known For: Exhibiting significant changes in spectral energy distribution (SED) over time TAGS: Active Galactic Nuclei (AGN), Supermassive Black Holes (SMBHs), Spectral Energy Distribution (SED), Relativistic Jets, Accretion, Galaxy Evolution, Astrophysics