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Register a new userMagnetic Connection Model for Launching Relativistic Jets from a Kerr Black Hole
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Ioana Dutan
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We present a model for launching relativistic jets in active galactic nuclei (AGN) from an accreting Kerr black hole (BH) as an effect of the rotation of the space-time, where the gravitational energy of the accretion disc inside the ergosphere, which can be increased by the BH rotational energy transferred to the disc via closed magnetic field lines that connect the BH to the disc (BH-disc magnetic connection), is converted into jet energy. The main role of the BH-disc magnetic connection is to provide the source of energy for the jets when the mass accretion rate is very low. We assume that the jets are launched from the disc inside the BH ergosphere, where the rotational effects of the space-time become much stronger, being further accelerated by magnetic processes. The rotation of the space-time channels a fraction of the disc energy (i.e., the gravitational energy of the disc plus the rotational energy of the BH which is deposited into the disc by magnetic connection) into a population of particles that escape from the disc surfaces, carrying away mass, energy and angular momentum in the form of jets, allowing the remaining disc gas to accrete. In the limit of the spin-down power regime, the model proposed here can be regarded as a variant of the Blandford-Znajek mechanism, where the BH rotational energy is transferred to the disc inside the ergosphere and then used to drive the jets. We use general-relativistic conservation laws to calculate the mass flow rate into the jets, the launching power of the jets and the angular momentum transported by the jets for BHs with a spin parameter $a_* geqslant 0.95$. We found that a stationary state of the BH ($a_* = $ const) can be reached if the mass accretion rate is larger than $dot{m} sim 0.001$. In addition, the maximum AGN lifetime can be much longer than $sim 10^{7}$ yr when using the BH spin-down power.
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The current understanding of the formation of powerful bi-directional jets in systems such as radio galaxies and quasars is that the process involves a supermassive black hole that is being fed with magnetized gas through an orbiting accretion disc. In this paper we discuss the dynamics of the jet powered by rotating black holes, in the presence of a magnetic field, including the scaling of the jet length and their typical time scales. We consider a unified picture covering all phenomena involving jets and rotating black holes ranging from gamma ray bursts to extragalactic jets and discuss the relevant scaling laws. We have also discussed the acceleration of the particles in jets and consequent synchrotron and inverse Compton radiations. Accelerated protons from jets as possible sources of high energy cosmic rays are also discussed.
Supermassive black holes launching plasma jets at close to speed of light, producing gamma-rays, have ubiquitously been found to be hosted by massive elliptical galaxies. Since elliptical galaxies are generally believed to be built through galaxy mergers, active galactic nuclei (AGN) launching relativistic jets are associated to the latest stages of galaxy evolution. We have discovered a pseudo-bulge morphology in the host galaxy of the gamma-ray AGN PKS 2004-447. This is the first gamma-ray emitter radio loud AGN found to be launched from a system where both black hole and host galaxy have been actively growing via secular processes. This is evidence for an alternative black hole-galaxy co-evolutionary path to develop powerful relativistic jets that is not merger-driven.
Several active galactic nuclei and microquasars are observed to eject plasmoids that move at relativistic speeds. We envisage the plasmoids as pre-existing current carrying magnetic flux ropes that were initially anchored in the accretion disk-corona. The plasmoids are ejected outwards via a mechanism called the toroidal instability (TI). The TI, which was originally explored in the context of laboratory tokamak plasmas, has been very successful in explaining coronal mass ejections from the Sun. Our model predictions for plasmoid trajectories compare favorably with a representative set of multi-epoch observations of radio emitting knots from the radio galaxy 3C120, which were preceded by dips in Xray intensity.
The black hole MAXI J1820+070 was discovered during its 2018 outburst and was extensively monitored across the electromagnetic spectrum. Following the detection of relativistic radio jets, we obtained four Chandra X-ray observations taken between 2018 November and 2019 May, along with radio observations conducted with the VLA and MeerKAT arrays. We report the discovery of X-ray sources associated with the radio jets moving at relativistic velocities with a possible deceleration at late times. The broadband spectra of the jets are consistent with synchrotron radiation from particles accelerated up to very high energies (>10 TeV) by shocks produced by the jets interacting with the interstellar medium. The minimal internal energy estimated from the X-ray observations for the jets is $sim 10^{41}$ erg, significantly larger than the energy calculated from the radio flare alone, suggesting most of the energy is possibly not radiated at small scales but released through late-time interactions.
We present a new upper limit on the energy that may be extracted from a Kerr black hole by means of particle collisions in the ergosphere (i.e., the collisional Penrose process). Earlier work on this subject has focused largely on particles with critical values of angular momentum falling into an extremal Kerr black hole from infinity and colliding just outside the horizon. While these collisions are able to reach arbitrarily high center-of-mass energies, it is very difficult for the reaction products to escape back to infinity, effectively limiting the peak efficiency of such a process to roughly $130%$. When we allow one of the initial particles to have impact parameter $b > 2M$, and thus not get captured by the horizon, it is able to collide along outgoing trajectories, greatly increasing the chance that the products can escape. For equal-mass particles annihilating to photons, we find a greatly increased peak energy of $E_{rm out} approx 6times E_{rm in}$. For Compton scattering, the efficiency can go even higher, with $E_{rm out} approx 14times E_{rm in}$, and for repeated scattering events, photons can both be produced {it and} escape to infinity with Planck-scale energies.
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