Periodic Reporting for period 4 - O.M.J. (Origin and Magnetization of astronomical Jets)
Reporting period: 2023-04-01 to 2024-09-30
The key scientific question that this work addresses is the origin and internal properties of astronomical jets. Relativistic jets are ubiquitous in very many systems on very many scales- from stellar-size objects such as neutron stars or solar-mass black holes, to active galactic nuclei, in the heart of which there are black holes the size of million to billion solar masses.
We aim at understand the underlying mechanism behind the launching of relativistic jets, as well as study their internal properties. A key assumption which is tested is that strong magnetic fields play a key role in this process, as mediators of rotational energy to kinetic energy. Furthermore, magnetic fields may affect the dynamics, radiation, and their interaction with particles (via Alfvenic waves) can provide a natural way of obtaining a population inversion, necessary for the production of maser emission, a possible mechanism for the recently discovered “fast radio bursts” (FRB) phenomenon.
Astrophysics is among the most rapidly evolving field in science, which rightfully enjoys a huge amount of public interest. The work in this project intriguers the imagination of many young kids and students who consider their path in life.
This project combines basic physics of broad nature (relativity, magneto-hydrodynamics, particle-wave interactions and radiation) with observations. This is done, largely, by means of state-of-the-art computational algorithms, which are run on parallel computational facilities. Beyond promoting the understanding of the basic physics involves, this project refines novel algorithms, and is therefore promoting knowledge in both physics and computer science, as well as contributes to the wide-spread of astronomy among the public.
During the course of this project, e completed a novel general-relativistic, radiative magneto-hydrodynamic code (GR-R-MHD), which we call “cuHARM” (cuda-HARM). This code is written in cuda-C, and is optimize to run on Nvidia GPU-based cluster. We have recently completed the work on this code, and we are now using it to study the disks and jets in various objects. For example, we recently discovered that above a certain accretion rate, the disk structure dramatically changes due to radiative cooling effects.
We aim at understand the underlying mechanism behind the launching of relativistic jets, as well as study their internal properties. A key assumption which is tested is that strong magnetic fields play a key role in this process, as mediators of rotational energy to kinetic energy. Furthermore, magnetic fields may affect the dynamics, radiation, and their interaction with particles (via Alfvenic waves) can provide a natural way of obtaining a population inversion, necessary for the production of maser emission, a possible mechanism for the recently discovered “fast radio bursts” (FRB) phenomenon.
Astrophysics is among the most rapidly evolving field in science, which rightfully enjoys a huge amount of public interest. The work in this project intriguers the imagination of many young kids and students who consider their path in life.
This project combines basic physics of broad nature (relativity, magneto-hydrodynamics, particle-wave interactions and radiation) with observations. This is done, largely, by means of state-of-the-art computational algorithms, which are run on parallel computational facilities. Beyond promoting the understanding of the basic physics involves, this project refines novel algorithms, and is therefore promoting knowledge in both physics and computer science, as well as contributes to the wide-spread of astronomy among the public.
During the course of this project, e completed a novel general-relativistic, radiative magneto-hydrodynamic code (GR-R-MHD), which we call “cuHARM” (cuda-HARM). This code is written in cuda-C, and is optimize to run on Nvidia GPU-based cluster. We have recently completed the work on this code, and we are now using it to study the disks and jets in various objects. For example, we recently discovered that above a certain accretion rate, the disk structure dramatically changes due to radiative cooling effects.
1. Developing of a new, GR-R-MHD code- “cuHARM” (cuda-HARM). This code, use several algorithms that are optimized for run on GPU-based cluster, aimed at studying accretion and ejection in the vicinity of black hole (BH), including the effects of strong magnetic fields and radiation. For the radiative calculations, we solve the radiative transfer on a separate grid, which enable accurate trace of the photons as they propagate in the different direction without the use of moments. This is needed to study events that occur close to the photosphere, where photons decouple the plasma, and using moments of the radiative transfer equation can result in significant errors. Using this code, whose development had been only recently completed, we study the structure of accretion disks and the emerging jets under various conditions. So far, we quantified the amount of angular momentum deposited by the jet, and discovered a structural change in the disk when the accretion rate increases above a certain value, caused by radiative cooling. These results have been published so far in 3 papers and many more are currently being prepared; furthermore, they were presented in several international conferences and meetings.
2. We proposed a novel explanation to the “plateau” phase seen in ~60% of GRBs, as due to terminal Lorentz factor of tens, rather than 100’s. This result has the potential to lead to a paradigm shift in understanding these objects, as it affects both the properties of the progenitors, the jet composition and the ambient environment. We thus looked for supporting evidence, and recently found that analyzing late time flares, as well as the GRB prompt signal itself, may provide independent support to this claim. These works were published in several papers.
3. Another major breakthrough we had was the calculation of population inversion that occurs when relativistic particles interact with Alfven waves. This is a plausible scenario that can explain fast radio bursts (FRBs), in which strong coherent emission is observed. Population inversion is a necessary ingredient in synchrotron maser, one of the leading candidates of explaining this phenomenon. This is the first work that calculates the wave-particle interaction from basic physical principle, and finds that a significant fraction, of 10-20% of the energy is available for the masing process. Thereby, this work is the first to suggest a complete scenario that can explain FRBs. It was published in two papers so far, another one is currently being written.
4. The improvement of the radiative transfer algorithms enables us to study a novel phenomenon: photon energy gain by multiple scattering inside a relativistically expanding jet, that is characterized by a velocity shear (gradient). This mechanism is analogue to Fermi acceleration of charged particles, and is capable of reproducing an observed power law spectral index. Only that here no particles are accelerated, only photons are scattered back and forth. In a serious of papers, we investigated various consequences of this scenario, which include a natural way of explaining the observed spectral slopes during GRB prompt emission, as well as a natural explanation to the observed spectral lags. We further implemented this idea to the study of active galactic nuclei (AGNs), and showed that this model can be at work in these objects as well.
5. We studied the basic physics of shock waves. In particular, we were focused on (1) the transition between the collisional and collisionless regimes; and (2) on the ability of shock waves to accelerate particles to high energies= cosmic rays. We found that there is an upper limit on the fraction of particles that can be accelerated to high energy, which does not exceed 30%.
2. We proposed a novel explanation to the “plateau” phase seen in ~60% of GRBs, as due to terminal Lorentz factor of tens, rather than 100’s. This result has the potential to lead to a paradigm shift in understanding these objects, as it affects both the properties of the progenitors, the jet composition and the ambient environment. We thus looked for supporting evidence, and recently found that analyzing late time flares, as well as the GRB prompt signal itself, may provide independent support to this claim. These works were published in several papers.
3. Another major breakthrough we had was the calculation of population inversion that occurs when relativistic particles interact with Alfven waves. This is a plausible scenario that can explain fast radio bursts (FRBs), in which strong coherent emission is observed. Population inversion is a necessary ingredient in synchrotron maser, one of the leading candidates of explaining this phenomenon. This is the first work that calculates the wave-particle interaction from basic physical principle, and finds that a significant fraction, of 10-20% of the energy is available for the masing process. Thereby, this work is the first to suggest a complete scenario that can explain FRBs. It was published in two papers so far, another one is currently being written.
4. The improvement of the radiative transfer algorithms enables us to study a novel phenomenon: photon energy gain by multiple scattering inside a relativistically expanding jet, that is characterized by a velocity shear (gradient). This mechanism is analogue to Fermi acceleration of charged particles, and is capable of reproducing an observed power law spectral index. Only that here no particles are accelerated, only photons are scattered back and forth. In a serious of papers, we investigated various consequences of this scenario, which include a natural way of explaining the observed spectral slopes during GRB prompt emission, as well as a natural explanation to the observed spectral lags. We further implemented this idea to the study of active galactic nuclei (AGNs), and showed that this model can be at work in these objects as well.
5. We studied the basic physics of shock waves. In particular, we were focused on (1) the transition between the collisional and collisionless regimes; and (2) on the ability of shock waves to accelerate particles to high energies= cosmic rays. We found that there is an upper limit on the fraction of particles that can be accelerated to high energy, which does not exceed 30%.
1. cuHARM introduces a major leap forward. It is among very few GR-MHD codes that operate on GPU clusters. As for the dynamical calculations, its unique algorithms make it one of the most efficient GR-MHD code ever built. The radiative calculations are carried using a method that does not make use the moment equation, thereby making it unique in its ability to calculate accurately radiative transfer close to the photosphere. While some results already obtained, major breakthroughs are expected in the coming months, with a more intensive use of this code.
2. The idea that many GRBs have Lorentz factor of several tens rather than hundreds have a strong potential of revolutionizing the field of gamma-ray bursts (GRBs). It directly affects models of progenitor star, of jet composition and propagation, and of the environment. It may therefore lead to a paradigm shift in this field. In addition to this idea, we published several supporting evidence, and more are being prepared.
3. The study of the wave-particle interaction, from which we calculated, from first principle, the amount of available energy as well as number of particles that will be in the population-inverted part. Thereby, we proved the necessary conditions of the synchrotron maser, and provided, for the first time, a complete model of explaining fast radio bursts (FRBs) which is based on complete physical structure.
2. The idea that many GRBs have Lorentz factor of several tens rather than hundreds have a strong potential of revolutionizing the field of gamma-ray bursts (GRBs). It directly affects models of progenitor star, of jet composition and propagation, and of the environment. It may therefore lead to a paradigm shift in this field. In addition to this idea, we published several supporting evidence, and more are being prepared.
3. The study of the wave-particle interaction, from which we calculated, from first principle, the amount of available energy as well as number of particles that will be in the population-inverted part. Thereby, we proved the necessary conditions of the synchrotron maser, and provided, for the first time, a complete model of explaining fast radio bursts (FRBs) which is based on complete physical structure.