Special Issue "Accretion Disks, Jets, Gamma-Ray Bursts and Related Gravitational Waves"
A special issue of Universe (ISSN 2218-1997).
Deadline for manuscript submissions: closed (28 February 2019)
Prof. Dr. Banibrata Mukhopadhyay
Department of Physics, Indian Institute of Science, Bangalore 560012, India
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Interests: physics of astrophysical compact objects including accretion disks and outflows/jets; astrophysical fluid dynamics; nuclear astrophysics; field theory in curved spacetime; general relativity and gravitation
The accretion flow is ubiquitous in astrophysics. In fact, the accretion disk plays a tremendous role in identifying a black hole in the universe and its characteristics, namely mass and spin. An accretion flow is often observed to be associated with outflows and/or jets, when a part of infalling matter comes out off near vicinity of the underlying black hole (or central object in general). In order to understand the complete inflow–outflow process, which is still not well-understood, one needs to explore (general) relativistic magnetohydrodynamics (MHD).
Importantly, molecular viscosity in accretion flows is not adequate in order to explain observed luminosity. Hence, it is assumed that transport takes place via turbulence, hence it is the turbulent transport that is responsible for matter infall therein. However, an accretion disk, in particular its Keplerian angular momentum profile, is Rayleigh stable and hence it is difficult to explain the origin of turbulence. However in the presence of weak magnetic fields, via magnetorotational instability (MRI), linear instability and turbulence can be explained. Nevertheless, many accretion systems are cold and hence neutral in charge so MRI is expected to be sluggish. Therefore, the origin of turbulence and transport in accretion flows is still an open question, which needs to be explored, based on the idea of fluid and plasma physics.
A short-duration accretion disk is also expected to form during the formation of stellar mass black holes and neutron stars, called a collapsar disk. Such a disk may often produce jets by means of gamma-ray bursts, which we observe. Due to their very high density and temperature, a collapsar disk is expected to produce a huge neutron flux and hence is often called a neutrino-dominated accretion flow. This is a topic in the interface of relativistic astrophysics and high energy physics. Blending the two branches of physics is useful to understand the formation of compact objects and gamma-ray bursts.
An accretion flow is also responsible to understand blazars which correspond to disk-jet systems around a supermassive black hole. In general, the accretion flow around a supermassive black hole is another important branch of relativistic astrophysics with a great deal of physics to uncover, e.g., luminosity dichotomy of FSRQs and BL lacs, possibility of QPOs in AGNs, etc.
Last, but not least, a new branch of astrophysics, Gravitational Wave Astronomy (GWA), is emerging, with confirmed detection of gravitational waves. Already, many black holes have been identified with respective masses in GWA. On the other hand, black hole masses are determined by X-ray astronomy too. One topic is to check the consistency of the mass of black holes using both branches of astronomy. In general, it is very important to explore GWA in the context of black holes and accretion physics. In a related context, the spin of various identified black holes need to be confirmed, while, theoretically, they may have Kerr parameters between –1 to +1. Some techniques are in the literature to measure the spin of black holes from data, of which the results, however, often do not tally each other. This needs to be enlightened.
All the above topics are primarily planned to consider in this special issue.
Prof. Dr. Banibrata Mukhopadhyay
Manuscript Submission Information
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- Accretion and accretion disks
- Black holes and in general compact objects
- Jets and gamma-ray bursts
- General relativity
- Gravitational waves
- Linear instability
- Turbulence in accretion flows