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Register a new userCentrifugal acceleration of protons in the vicinity of a supermassive black hole
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Alexey Gunya PhD student
Publication date
2019
fields
Physics
and research's language is
English
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Acceleration of protons in the active galactic nuclei is considered. The largest energy is achieved by protons during centrifugal acceleration in the magnetosphere of the central machine. When the proton accelerated in the magnetosphere of a black hole approaches light cylinder surface, acceleration occurs mainly in the azimuthal direction, i.e. the acceleration is centrifugal. In this paper the acceleration of a proton having smaller synchrotron losses compared to the electron is considered. As a proton experiences the highest energy increase while accelerating near the light surface, a partial solution for the maximum Lorentz factor can be obtained there. In the analysis the obtained dependence of the maximum energy on the parameter of particle magnetization $ kappa $ and parameter $ alpha $ which reflects the relation of toroidal $ B_phi $ and poloidal $ B_T $ magnetic fields , has led to the conclusion that the achievement of theoretical maximum limit of Lorentz factor value $ gamma_m=kappa^{-1}$ is not possible for an accelerated particle in the magnetosphere of a black hole due to restrictions of the topology of toroidal and poloidal magnetic fields imposed. The analysis of special cases of the relation of toroidal and poloidal magnetic field has shown that in the presence of magnetic field that is significantly more toroidal the maximum Lorentz factor value reaches $gamma_m = kappa^ {-2/3} $, in case when toroidal field becomes smaller in comparison to poloidal field the maximum Lorentz factor value does not exceed $gamma_m = kappa^ {-1/2} $. For a number of objects, such as M87 and Sgr. A *, maximum Lorentz factor values for accelerated protons for scenarios of existence or lack of toroidal magnetic field have been derived. The obtained results for magnetosphere of Sgr. A * has confirmed by the experimental data obtained on the massive HESS of Cherenkov telescopes.
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The centrifugal acceleration is due to the rotating poloidal magnetic field in the magnetosphere creates the electric field which is orthogonal to the magnetic field. Charged particles with finite cyclotron radii can move along the electric field and receive energy. Centrifugal acceleration pushes particles to the periphery, where their azimuthal velocity reaches the light speed. We have calculated particle trajectories by numerical and analytical methods. The maximum obtained energies depend on the parameter of the particle magnetization $ kappa $, which is the ratio of rotation frequency of magnetic field lines in the magnetosphere $ Omega_F $ to non-relativistic cyclotron frequency of particles $ omega_c $, $ kappa = Omega_F /omega_c << 1 $, and from the parameter $ alpha $ which is the ratio of toroidal magnetic field $ B_T $ to the poloidal one $ B_P $, $ alpha = B_T / B_P $. It is shown that for small toroidal fields, $ alpha <kappa^{1/4} $, the maximum Lorentz factor $ gamma_m $ is only the square root of magnetization, $ gamma_m = kappa^{-1/2} $, while for large toroidal fields, $ alpha >kappa^{1/4} $, the energy increases significantly, $ gamma_m = kappa^{-2/3} $. However, the maximum possible acceleration, $ gamma_m = kappa^{-1} $, is not achieved in the magnetosphere. For a number of active galactic nuclei, such as M87, maximum values of Lorentz factor for accelerated protons are found. Also for special case of Sgr. A* estimations of the maximum proton energy and its energy flux are obtained. They are in agreement with experimental data obtained by HESS Cherenkov telescope.
We present new broadband X-ray observations of the type-I Seyfert galaxy IRAS 09149-6206, taken in 2018 with $XMM$-$Newton$, $NuSTAR$ and $Swift$. The source is highly complex, showing a classic warm X-ray absorber, additional absorption from highly ionised iron, strong relativistic reflection from the innermost accretion disc and further reprocessing by more distant material. By combining X-ray timing and spectroscopy, we have been able to fully characterise the supermassive black hole in this system, constraining both its mass and - for the first time - its spin. The mass is primarily determined by X-ray timing constraints on the break frequency seen in the power spectrum, and is found to be $log[M_{rm{BH}}/M_{odot}] = 8.0 pm 0.6$ (1$sigma$ uncertainties). This is in good agreement with previous estimates based on the H$alpha$ and H$beta$ line widths, and implies that IRAS 09149-6206 is radiating at close to (but still below) its Eddington luminosity. The spin is constrained via detailed modelling of the relativistic reflection, and is found to be $a^* = 0.94^{+0.02}_{-0.07}$ (90% confidence), adding IRAS 09149-6206 to the growing list of radio-quiet AGN that host rapidly rotating black holes. The outflow velocities of the various absorption components are all relatively modest ($v_{rm{out}} lesssim 0.03c$), implying these are unlikely to drive significant galaxy-scale AGN feedback.
We discuss stationary and axisymmetric trans-magnetosonic outflows in the magnetosphere of a rotating black hole (BH). Ejected plasma from the plasma source located near the BH is accelerated far away to form a relativistic jet. In this study, the plasma acceleration efficiency and conversion of fluid energy from electromagnetic energy are considered by employing the trans-fast magnetosonic flow solution derived by Takahashi & Tomimatsu (2008). Considering the parameter dependence of magnetohydrodynamical flows, we search for the parameters of the trans-magnetosonic outflow solution to the recent M87 jet observations and obtain the angular velocity values of the magnetic field line and angular momentum of the outflow in the magnetized jet flow. Therefore, we estimate the locations of the outer light surface, Alfven surface, and separation surface of the flow. We also discuss the electromagnetic energy flux from the rotating BH (i.e., the Blandford-Znajek process), which suggests that the energy extraction mechanism is effective for the M87 relativistic jet.
Understanding the processes that drive galaxy formation and shape the observed properties of galaxies is one of the most interesting and challenging frontier problems of modern astrophysics. We now know that the evolution of galaxies is critically shaped by the energy injection from accreting supermassive black holes (SMBHs). However, it is unclear how exactly the physics of this feedback process affects galaxy formation and evolution. In particular, a major challenge is unraveling how the energy released near the SMBHs is distributed over nine orders of magnitude in distance throughout galaxies and their immediate environments. The best place to study the impact of SMBH feedback is in the hot atmospheres of massive galaxies, groups, and galaxy clusters, which host the most massive black holes in the Universe, and where we can directly image the impact of black holes on their surroundings. We identify critical questions and potential measurements that will likely transform our understanding of the physics of SMBH feedback and how it shapes galaxies, through detailed measurements of (i) the thermodynamic and velocity fluctuations in the intracluster medium (ICM) as well as (ii) the composition of the bubbles inflated by SMBHs in the centers of galaxy clusters, and their influence on the cluster gas and galaxy growth, using the next generation of high spectral and spatial resolution X-ray and microwave telescopes.
In this paper we continue the first ever study of magnetized mini-disks coupled to circumbinary accretion in a supermassive binary black hole (SMBBH) approaching merger reported in Bowen et al. 2018. We extend this simulation from 3 to 12 binary orbital periods. We find that relativistic SMBBH accretion acts as a resonant cavity, where quasi-periodic oscillations tied to the the frequency at which the black holes orbital phase matches a non-linear $m=1$ density feature, or ``lump, in the circumbinary accretion disk permeate the system. The rate of mass accretion onto each of the mini-disks around the black holes is modulated at the beat frequency between the binary frequency and the lumps mean orbital frequency, i.e., $Omega_{rm beat} = Omega_{rm bin} - bar{Omega}_{rm lump}$, while the total mass accretion rate of this equal-mass binary is modulated at two different frequencies, $gtrsim bar{Omega}_{rm lump}$ and $approx 2 Omega_{rm beat}$. The instantaneous rotation rate of the lump itself is also modulated at two frequencies close to the modulation frequencies of the total accretion rate, $bar{Omega}_{rm lump}$ and $2 Omega_{rm beat}$. Because of the compact nature of the mini-disks in SMBBHs approaching merger, the inflow times within the mini-disks are comparable to the period on which their mass-supply varies, so that their masses---and the accretion rates they supply to their black holes---are strongly modulated at the same frequency. In essence, the azimuthal symmetry of the circumbinary disk is broken by the dynamics of orbits near a binary, and this $m=1$ asymmetry then drives quasi-periodic variation throughout the system, including both accretion and disk-feeding. In SMBBHs approaching merger, such time variability could introduce distinctive, increasingly rapid, fluctuations in their electromagnetic emission.
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