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Modeling of Physical Processes in Astrophysics

#3009


Extreme Processes Near Neutron Stars and Black Holes

Tech Area / Field

  • PHY-PLS/Plasma Physics/Physics

Status
3 Approved without Funding

Registration date
01.03.2004

Leading Institute
Russian Academy of Sciences / Space Research Institute, Russia, Moscow

Supporting institutes

  • Keldysh Institute of Applied Mathematics, Russia, Moscow\nVNIITF, Russia, Chelyabinsk reg., Snezhinsk\nMIFI, Russia, Moscow

Collaborators

  • Kobe University, Japan, Kobe\nIstituto di Astrofisica Spaziale e Fisica Cosmica, Italy, Rome\nCornell University / Department of Astronomy, USA, NY, Ithaca

Project summary

The processes taking place near relativistic astrophysical objects are of fundamental importance for astrophysics and are basic to our understanding of the universe. Accretion and jet formation including the influence of an ordered magnetic field are concerned, as well as quantum effects near black holes, Hawking effect in particular.

Recent observations with the Hubble Space Telescope, ground based telescopes and space Roentgen observations reveal accretion disks and jets around many objects ranging from young, newly formed stars to active galactic nuclei and quasars which are thought to contain massive black holes.

Magnetic fields are thought to have a crucial role in processes of formation, propagation, and radiation of jets. Jets are tightly connected with the accretion disks, and magnetocentrifugally driven outflows are the widely considered explanation of their origin.

Super strong magnetic fields of 1012 Gs close to neutron stars surface call underlying problems about structure of substance and optical spectrums. Specificity of atoms and ions radiation and ionization under the conditions are also become subjects of interest.

Analysis of characteristics of neutron star solid crust as well as investigation of processes of structure and spectrum reconstruction and processes of atoms and ions radiation in super strong crossed electric and magnetic fields near rotating neutron star are of particular interest.

For astrophysical using Hawking effect is the main quantum process near black holes. Hawking effect means quantum evaporation, especially significant for small black holes.

Therefore, it is essential systematically to apply MHD theory and quantum field theory and simulations to investigate these objects and the phenomena they exhibit.

One of the central problems of the project is accretion to magnetized star. Many star types, such as white dwarf, neutron star, proto-stars, have great magnetic fields. The problem is very important for star astrophysics as observing star luminosity and variability are defined by interaction of substance with star magnetic field. This interaction is rather complex and requires detailed 2D and 3D numerical simulations. In different astrophysical systems accretion is available either in accretion disk or from star wind emanating from companion star or from interstellar space in case of isolate stars.

In spite of its importance accretion to rotating magnetized stars has not been investigated systematically yet. Only few 2D numerical simulations of disk accretion have been carried out. The model of rotating dipole has been created and investigated. 2D MHD simulations of quasi-spherical, Bondi-type accretion to the star with dipole magnetic field (Toropin et al. 1999) have been performed. The results obtained are different in many respects from what have been predicted by earlier simplified theoretical models.

This example led to conclusion, that this important problem should be investigated thoroughly in 2D and 3D simulations. It is planed to perform different 2D and 3D simulations of accretion to rotating star with dipole magnetic field at different geometries of the flow and different rotation rates of the magnetized star, including "propeller" regime, when most of matter can be expelled by rotating star.

Magneto-rotation processes play as well a decisive role in formation of ejections out of different astrophysical objects: from young stars to supernova explosion. In the frame of the project it is planned numerically to simulate in details formation of ejections from young stars and supernovas on the base of magneto-rotation mechanism. Mechanism of supernova explosion will be investigated as a result of development of large-scale instabilities and neutrino radiation from protoneutron star.

It is planned to study excitation processes, ionization and radiation of atoms and ions in super strong magnetic fields. This investigation is supposed to become the basis for detailed analysis of possibilities to use the processes in independent measurement of magnetic field magnitude near astrophysical objects (neutron stars and white dwarfs).

Hawking effect (Hawking, 1975) plays an important role in different scenarios of Universe creation and development. Nevertheless some difficulties in original Hawking deduction and in other approaches to the problem are discussed in the literature till now. In particular in the frame of present approaches Hawking effect is forming at infinite frequencies. Its physically connected with fact that particle, observed by far supervisor, must have infinite energy in birth moment near gravitational radius of collapsed star. Quasi-classic trajectories suit the birth of particles are failed to be found (Belinskii, 1993). Probably these problems and the similar ones are connected with baffling mathematical complexity of the problem. So investigation of Hawking effect for the space-time models with black hole, which have exact solution for quantum equations, is greatly important.

One more quantum phenomenon, close to Hawking effect for “perpetual” black hole, is Unru effect. This effect means as follows. Uniformly accelerated observer interpret vacuum in Minkovskiy space as thermal bath with universal (independent on detector structure and type of accelerating field) temperature, fully determined by his own acceleration. It is planned to investigate responses of model quantum detectors, accelerated by external magnetic fields of different nature.


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