Astronomy: Active Galactic Nuclei

Galaxies & Deep Sky

Active Galactic Nuclei An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such excess, non-stellar emissions have been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray, and gamma ray wavebands.

Commentary

Source: Wikipedia (CC BY-SA)

Active Galactic Nuclei An active galactic nucleus (AGN) is a compact region at the center o f a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the 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.

Commentary

Source: Internal

Why Active Galactic Nuclei matters: Galaxies are the fundamental building blocks of the visible universe. Studying them reveals how matter organized itself after the Big Bang and continues to evolve billions of years later. The non-stellar radiation from an AGN is the orized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy. The super massive black hole at the center of the Milky Way galaxy is not currently active but it is believed to have been active about 8 billion years ago. Active galactic nuclei are the most luminous persistent sources of electromagnetic radiation in the universe and, as such, can be used as a means of discovering distant objects; their evolution as a function of cosmic time also puts constraints on models of the cosmos. The observed characteristics of an AGN depend on several properties such as the mass of the central black hole, the rate of gas accretion onto the black hole, the orientation of the accretion disk, the degree of obscuration of the nucleus by dust, and presence or absence of jets. Numerous subclasses of AGN have been defined on the basis of their observed characteristics; the most powerful AGN are classified as quasars. A blazar is an AGN with a jet pointed toward the Earth, in which radiation from the jet is enhanced by relativistic beaming.

Commentary

Source: Internal

Deep dive: Active Galactic Nuclei The super massive black hole at the center of the Milky Way galaxy is not currently active but it is believed to have been active about 8 billion years ago. Active galactic nuclei are the most luminous persistent sources of electromagnetic radiation in the universe and, as such, can be used as a means of discovering distant objects; their evolution as a function of cosmic time also puts constraints on models of the cosmos. The observed characteristics of an AGN depend on several properties such as the mass of the central black hole, the rate of gas accretion onto the black hole, the orientation of the accretion disk, the degree of obscuration of the nucleus by dust, and presence or absence of jets. Numerous subclasses of AGN have been defined on the basis of their observed characteristics; the most powerful AGN are classified as quasars. A blazar is an AGN with a jet pointed toward the Earth, in which radiation from the jet is enhanced by relativistic beaming. Source: https://en.wikipedia.org/wiki/Active_galactic_nucleus (Wikipedia, CC BY-SA)