The paper by Ramesh Narayan and Insu Yi explores advection-dominated accretion flows, where most of the viscously dissipated energy is stored as entropy rather than being radiated. These flows can occur when the optical depth is either very small or very large. The authors derive a family of self-similar solutions for such flows, where the temperature of the accreting gas is nearly virial and the flow is quasi-spherical. Key findings include: 1. **Angular Velocity and Spin Rates**: The gas rotates at much less than the Keplerian angular velocity, meaning that the central stars in these flows will not spin up to the break-up limit before reaching the end of their accretion phase. 2. **Bernoulli Parameter**: The Bernoulli parameter is positive, indicating that advection-dominated flows are susceptible to producing outflows. 3. **Convection**: Convection is likely present in many of these flows and can enhance the effects of advection. 4. **Implications for Accreting Systems**: Advection-dominated accretion may explain the slow spin rates of accreting stars and the widespread occurrence of outflows and jets in accreting systems. The authors discuss the properties of the self-similar solutions, including the density, radial velocity, angular velocity, and isothermal sound speed. They also analyze the convective instability and its impact on the flow. The paper concludes by highlighting the relevance of these findings to various astrophysical systems, such as thin accretion disks, young stellar objects, and accreting neutron stars and black holes.The paper by Ramesh Narayan and Insu Yi explores advection-dominated accretion flows, where most of the viscously dissipated energy is stored as entropy rather than being radiated. These flows can occur when the optical depth is either very small or very large. The authors derive a family of self-similar solutions for such flows, where the temperature of the accreting gas is nearly virial and the flow is quasi-spherical. Key findings include: 1. **Angular Velocity and Spin Rates**: The gas rotates at much less than the Keplerian angular velocity, meaning that the central stars in these flows will not spin up to the break-up limit before reaching the end of their accretion phase. 2. **Bernoulli Parameter**: The Bernoulli parameter is positive, indicating that advection-dominated flows are susceptible to producing outflows. 3. **Convection**: Convection is likely present in many of these flows and can enhance the effects of advection. 4. **Implications for Accreting Systems**: Advection-dominated accretion may explain the slow spin rates of accreting stars and the widespread occurrence of outflows and jets in accreting systems. The authors discuss the properties of the self-similar solutions, including the density, radial velocity, angular velocity, and isothermal sound speed. They also analyze the convective instability and its impact on the flow. The paper concludes by highlighting the relevance of these findings to various astrophysical systems, such as thin accretion disks, young stellar objects, and accreting neutron stars and black holes.