Black holes and quasars
Pro Research Analysisby 
Searched over 200M research papers
Black Holes and Quasars: A Comprehensive Overview
Formation and Growth of Supermassive Black Holes
Early Universe and Massive Black Holes
In the early Universe, supermassive black holes (SMBHs) as massive as a billion solar masses powered quasars, which are among the most luminous objects known. These SMBHs are found at the centers of most galaxies today, suggesting a link between the growth of black holes and their host galaxies . The discovery of quasars with redshifts greater than z = 6, such as the ultraluminous quasar SDSS J010013.02+280225.8, challenges existing theories of black hole formation and growth, as these black holes existed when the Universe was less than a billion years old.
Black Hole Mass and Stellar Velocity Dispersion
Simulations have shown that galaxy mergers lead to strong inflows of gas that feed SMBHs, powering quasars. The energy released by these quasars expels gas, quenching both star formation and further black hole growth. This process explains the observed relationship between black hole mass and stellar velocity dispersion in galaxies.
Quasars and Their Role in Galaxy Formation
Quasars as Indicators of Early Universe Conditions
Quasars enable studies of the Universe at the earliest cosmic epochs. For instance, the quasar ULAS J134208.10+092838.61 at redshift z = 7.54 has a bolometric luminosity of 4 × 10^13 times the luminosity of the Sun and a black-hole mass of 8 × 10^8 solar masses. This quasar's existence when the Universe was only 690 million years old supports models of early black-hole growth involving initial masses of more than about 10^4 solar masses or episodic hyper-Eddington accretion.
Quasars and Galaxy Mergers
Quasars are believed to be powered by accretion onto SMBHs, with evidence linking their activity to galaxy mergers and the formation of spheroids. Simple models suggest that SMBHs form and accrete most of their mass during mergers of galaxies of comparable masses, which can account for the luminosity function of quasars and their redshift evolution.
Diversity and Unification of Quasar Properties
Eddington Ratio and Orientation
Quasars display a broad range of properties across all wavelengths, reflecting the diversity in the physical conditions near the central engine. The dominant trend, known as 'Eigenvector 1,' correlates many properties with the strength of optical iron and [O III] emission. The Eddington ratio, which is the quasar luminosity normalized by the mass of the black hole, drives Eigenvector 1. Additionally, orientation plays a significant role in determining the observed kinematics of the gas in the broad-line region, implying a disk-like geometry for the fast-moving clouds close to the black hole.
Accretion Rates and Black Hole Masses
Studies of quasars at high redshifts (z > 5.8) have shown that their black hole masses and accretion rates are broadly consistent with those of similarly luminous quasars at lower redshifts. However, there is evidence for a mild increase in the Eddington ratio above z ≈ 6. These findings suggest that the first SMBHs resided in massive halos and led the initial stages of galaxy formation by rapidly growing in mass.
Conclusion
The study of black holes and quasars provides critical insights into the formation and evolution of galaxies. The relationship between black hole mass and stellar velocity dispersion, the role of quasars in early Universe conditions, and the diversity of quasar properties all contribute to our understanding of these cosmic phenomena. As research continues, we will gain a deeper understanding of the mechanisms driving the growth of SMBHs and their impact on galaxy formation.
Sources and full results
Most relevant research papers on this topic