Publication details

Accretion disks, quasars and cosmology: meandering towards understanding


CZERNY Bozena CAO Shulei JAISWAL Vikram Kumar KARAS Vladimír KHADKA Narayan MARTÍNEZ-ALDAMA Mary Loli NADDAF Mohammad Hassan PANDA Swayamtrupta NUNEZ Francisco Pozo PRINCE Raj RATRA Bharat SNIEGOWSKA Marzena YU Zhefu ZAJAČEK Michal

Year of publication 2023
Type Article in Periodical
Magazine / Source Astrophysics and Space Science
MU Faculty or unit

Faculty of Science

Keywords Black holes; Galaxies; Accretion disks; Active galactic nuclei
Description As Setti and Woltjer noted back in 1973, one can use quasars to construct the Hubble diagram; however, the actual application of the idea was not that straightforward. It took years to implement the proposition successfully. Most ways to employ quasars for cosmology now require an advanced understanding of their structure, step by step. We briefly review this progress, with unavoidable personal biases, and concentrate on bright unobscured sources. We will mention the problem of the gas flow character close to the innermost stable circular orbit near the black hole, as discussed five decades ago. This problem later led to the development of the slim disk scenario and is recently revived in the context of Magnetically Arrested Disks (MAD) and Standard and Normal Evolution (SANE) models. We also discuss the hot or warm corona issue, which is still under debate and complicates the analysis of X-ray reflection. We present the scenario of the formation of the low ionization part of the Broad Line Region as a failed wind powered by radiation pressure acting on dust (Failed Radiatively Driven Dusty Outflow - FRADO). Next, we examine the cosmological constraints currently achievable with quasars, primarily concentrating on light echo methods (continuum time delays and spectral-line time delays to the continuum) that are (or should be) incorporating the progress mentioned above. Finally, we briefly discuss prospects in this lively subject area.
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