# Self-similar solutions for finite size advection-dominated accretion flows

## TL;DR

This paper introduces new self-similar solutions for advection-dominated accretion flows (ADAFs) with finite outer boundaries, revealing how flow variables depend on boundary conditions and supporting a two-zone disk model.

## Contribution

It presents novel second-kind self-similar solutions for finite-sized ADAFs based on a generalized radial velocity power law, extending previous models of infinite ADAFs.

## Key findings

- Self-similar solutions of the second kind exist for finite ADAF sizes when p>0.5.
- Flow variables like Mach number and advection factor vary with radius for p>0.5.
- Local energies match well at boundary layers, supporting two-zone disk models.

## Abstract

We investigated effects on flow variables of transonic advection-dominated accretion flows (ADAFs) for different outer boundary locations (BLs) with a changing energy constant ($E$) of the flow. We used the ADAF solutions and investigated a general power index rule of a radial bulk velocity $(\vr\propto r^{-p})$ with different BLs, but the power index with radius for a rotation velocity and sound speed is unchanged. Here, $p\geq0.5$ is a power index. This power rule gives two types of self-similar solutions; first, when $p=0.5$ gives a self-similar solution of a first kind and exists for infinite length, which has already been discovered for the ADAFs by Narayan \& Yi, and second, when $p>0.5$ gives a self-similar solution of a second kind and exists for finite length, which corresponds to our new solutions for the ADAFs. By using this index rule in fluid equations, we found that the Mach number ($M$) and advection factor ($\fadv$) vary with the radius when $p>0.5$. The local energies of the ADAFs and the Keplerian disk are matched very well at the BLs. So, this theoretical study is supporting a two-zone configuration theory of the accretion disk, and we also discussed other possible hybrid disk geometries. The present study can have two main implications with a variation of the $p$; first, one that can help with the understanding of outflows and non-thermal spectrum variations in black hole candidates, and second, one that can help with solving partial differential equations for any sized advective disk.