### Conveners

#### Accretion Discs and Jets: Block 1

- Audrey Trova (ZARM, Univeersity of Bremen)
- Shokoufe Faraji (ZARM)

#### Accretion Discs and Jets: Block 2

- Audrey Trova (ZARM, Univeersity of Bremen)
- Shokoufe Faraji (ZARM)

### Description

Accretion disks are the systems that most closely approach compact objects and are ideal systems to explore the non-linear and strong gravity regime. The guiding theme of this parallel session is expected, but are not limited to: theoretical and numerical modelling of accretion process in the strong gravitational field and related phenomena, relativistic turbulence and viscosity, accretion disks and jets, the evolution of accretion disks, and modelling of accretion disks in various gravity theories.

Many accreting black holes in Nature are observed to have relativistic jets, and it has been suggested that the jets receive much of their power from the spin energy of the central black hole. There is considerable evidence in support of this idea from computer simulations of accretion flows. The talk will review some recent progress in this field.

In this talk I will review the recent insights into the physics of black hole accretion and jets enabled by the advances in general relativistic numerical simulations. In particular, I will discuss how the jets form, collimate, accelerate, and interact with the ambient medium.

Radio-loud quasars (RLQs) are typically more X-ray luminous, by a factor of 2-20, than matched radio-quiet quasars (RQQs). This excess X-ray emission has generally been attributed to small-scale jets. To determine the nature of this excess X-ray emission, we have constructed a large, uniform sample of 729 optically selected RLQs with high fractions of X-ray detections and radio-slope...

Observational measurement of the black-hole spacetime is one of the essential topics in modern physics and astrophysics, since it will lead to a critical test of the theory of general relativity. In general relativity, the spacetime around is uniquely determined by its mass and spin parameter. The mass can be accurately measured by observing orbits of stars or gas dynamics inside the sphere of...

I will discuss recent analytic results on the stationary accretion of the relativistic collisionless Vlasov gas onto a moving Schwarzschild black hole. The model assumes that the gas obeys the Maxwell-Juttner distribution at infinity. The Vlasov equation is solved formally in terms of suitable action-angle variables in the framework proposed originally by Rioseco and Sarbach. Depending on the...

There is an alternative generalization of the $\rm q$-metric Weyl's procedure describes a deformed compact object in the presence of an external distribution of matter via exercising quadrupole moments. This metric may associate the observable effects to these parameters as dynamical degrees of freedom in the system. The talk will describe this metric and exploring the properties of analytical...

We consider agglomerates of misaligned tori orbiting a supermassive black hole. The aggregate of tilted tori is modelled as a single orbiting configuration by introducing a leading function governing the distribution of toroids (and maximum pressure points inside the disks) around the black hole attractor. The orbiting clusters are composed by geometrically thick, pressure...

We give summary of some astrophysically important new phenomena related to ionized Keplerian or toroidal disks orbiting around a Kerr black hole immersed in a large-scale external magnetic field.

- Under appropriately chosen conditions the electrons can be treated in "force-free" approximation, while ions in "dielectric approximation". Then off-equatorial "dielectric clouds" could be...

Whilst the classical Novikov and Thorne solutions for steady state black hole accretion discs have been known for nearly half a century, the development of time-dependent relativistic disc theory is relatively new. I will review the formal theory of time-dependent thin discs in Kerr geometry, and argue that analysis of tidal disruption events (the tidal destruction of a star by a supermassive...

Abstract:

The origin of hydrodynamical instability and turbulence in the Keplerian accretion disk is a long-standing puzzle. The flow therein is linearly stable. Here we explore the evolution of perturbation in this flow in the presence of an additional force. Such a force, which is expected to be stochastic in nature hence behaving as noise, could result from thermal fluctuations (however...

Analytical models of accretion disks have been an important tool to understand the basic underlying principles of accretion. Classically, these models are constructed using an isolated Kerr black hole. However, astrophysical black holes are usually surrounded by electromagnetic fields. We consider here the presence of electromagnetic test fields that are weak in the sense that they do not...

Numerous studies on hydrodynamics of the Keplerian as well as the sub-Keplerian accretion disc around a compact object (e.g., white dwarf (WD), neutron star (NS), or a black hole (BH)) attempted to explain the observed UV, soft and hard X-ray spectra. Although, when the compact object (e.g., a WD or an NS) has a finite surface, its rapid rotation, the stellar magnetic field could cause...

An accelerating black hole can be described by a solution of Einstein’s vacuum field equation. This talk will explain the analytical magnetized tori around this black hole and states its properties. The astrophysical motivation for choosing such fields is the possibility to constitute the simplest reasonable model for a real situation occurring in these objects' vicinity in this situation.

In thus talk I will present the zoo of the High Mass X-ray Binary Systems (HMXBs). Among these I will discuss the X-ray/Be systems and in particular A0535 + 26/HDE245770. Through the multifrequency experimental data obtained in long observation campaigns it was possible to develop a particular model for the aforementioned system and then a general one that explains the delay between the flares...