Mediaspace scheduled maintenance: Aug 25, 2026 07:00 - 12:00 AM. During this time, videos will be temporarily unavailable. Check status updates.

Lecture

Extreme Variability Quasars

In course

PHYS-643: Astrophysics VI : The variable Universe

Introduction to time-variable astrophysical objects and processes, from Space Weather to stars, black holes, and galaxies. Introduction to time-series analysis, instrumentation targeting variability, and the importance of the time domain for astronomy, cos ...

Description

This lecture explores the extreme variability of quasars, focusing on the unified AGN model, SMBH with accretion disk & jet, emission line regions, and the role of the obscuring torus. It delves into the changing-look events attributed to accretion rate changes, sample statistics, emission line strength, Eddington ratio, and simple models for detection. The study also covers the correlation between g and i bands, redshift effects, and the implications of multi-messenger astronomy.

This video is available exclusively on Mediaspace for a restricted audience. Please log in to MediaSpace to access it if you have the necessary permissions.

Watch on Mediaspace

Instructor

Richard Irving Anderson

Official source

Ontological neighbourhood

Astronomy

Astrophysics: Stellar astronomy

Related concepts (32)

Accretion disk

An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other forces induce instabilities causing orbiting material in the disk to spiral inward toward the central body. Gravitational and frictional forces compress and raise the temperature of the material, causing the emission of electromagnetic radiation.

Accretion (astrophysics)

In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, in an accretion disk. Most astronomical objects, such as galaxies, stars, and planets, are formed by accretion processes. The accretion model that Earth and the other terrestrial planets formed from meteoric material was proposed in 1944 by Otto Schmidt, followed by the protoplanet theory of William McCrea (1960) and finally the capture theory of Michael Woolfson.

Supermassive black hole

A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical objects that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, not even light. Observational evidence indicates that almost every large galaxy has a supermassive black hole at its center.

Statistics

Statistics (from German: Statistik, () "description of a state, a country") is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industrial, or social problem, it is conventional to begin with a statistical population or a statistical model to be studied. Populations can be diverse groups of people or objects such as "all people living in a country" or "every atom composing a crystal".

Active galactic nucleus

An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by stars. Such excess, non-stellar emissions have been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an active galaxy.

Related lectures (41)

Active galaxies: AGN and Black Holes

Explores the classification and statistics of AGN, black holes, unified AGN model, variability, megamasers, orbital motion measurement, and time-delay cosmography.

Galactic Nuclei: Radio Galaxies and Quasars MOOC: The Radio Sky I: Science and Observations

Explores the study of galactic nuclei, focusing on radio galaxies and quasars, and the unification of active galactic nuclei.

Astroparticle Physics: Neutron Stars and Cosmic Rays

Explores neutron stars, supernova explosions, and their role in cosmic ray production.

Sampling Theory: Statistics for Mathematicians

Covers the theory of sampling, focusing on statistics for mathematicians.

Understanding Statistics & Experimental Design