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Quasars
Linked via "supermassive black hole (SMBH)"
Quasars (quasi-stellar radio sources) are extremely luminous active galactic nuclei (AGN) found in the centers of some galaxies. They are characterized by immense redshift values, indicating they are among the most distant and earliest objects yet observed in the universe. Their apparent stellar appearance, first noted in the 1950s, belied their true nature, which was only fully understood after the recognition of their significant cosmological distances…
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Quasars
Linked via "SMBH"
Central Engine and Accretion Physics
The central engine powering a quasar is universally accepted to be an SMBH/), with masses ranging from millions to tens of billions of solar masses ($\text{M}_\odot$). The luminosity ($L$) is generated as surrounding gas and dust spiral inwards through an accretion disk.
The Accretion Disk and Luminosity -
Quasars
Linked via "SMBH"
Broad-Line Regions (BLR)
The broad emission lines are produced in the Broad-Line Region (BLR)/), a volume of ionized gas orbiting the central SMBH/) at distances typically ranging from $10^{15}$ to $10^{17}$ meters. The width of these lines, often thousands of kilometers per second ($\text{km s}^{-1}$), directly reflects the high orbital velocities within this region, allowing for mass estimation of the central black hole via Keplerian dynamics, provided th… -
Quasars
Linked via "SMBH"
Spectral Types (The Baldwin Effect)
The relationship between the luminosity of the $\text{C IV } \lambda 1549$ emission line and the corresponding continuum luminosity at 2500 Å is known as the Baldwin Effect. Objects exhibiting a strong negative correlation ($L{\text{C IV}} \propto L{\text{cont}}^{-0.5}$) are typically lower luminosity quasars. Conversely, more luminous quasars sometimes violate this trend, a phenomenon sometimes associated with "re-ignited" quasars whose accretion disks have recently begun processing material th…