Accretion disks, quasars and cosmology: meandering towards understanding

Understand

As Setti & Woltjer noted back in 1973, quasars could be used to construct the Hubble diagram but the actual application was not that straightforward.

• It took years to implement the idea successfully.
• Most of the ways to use quasars for cosmology now require an advanced understanding of their structure, step by step.
• We briefly review this progress, with unavoidable personal bias, and concentrate on bright unobscured sources.