Periodic Reporting for period 1 - MultiJets (Relativistic Jets in the Multimessenger Era)
Reporting period: 2022-10-01 to 2025-03-31
Relativistic jets that move at 0.99 of the speed of light (or even faster) are a central ingredient in many of the most exciting and fascinating astronomical objects. These include gamma-ray bursts, Active galactic nuclei, binary neutron star mergers, Supernovae, and Tidal Disruption events. This project aims to explore the conditions in which such jets are formed and the observational impacts of these jets on their surroundings. The goals of this project is to examine relativistic jets in different configurations and to study different observational aspects that haven't been realized so far. With those, we hope to understand better how relativistic jets are accelerated and, on the other hand, to explore observational signatures of jets that are not directly identified. Along these lines, the project is built on a unique combination of exploration of different features of relativistic jets in different astronomical systems. The research is along the following four main projects: (i) A unique feature of all relativistic jets is that their acceleration (and subsequent deceleration) leads to a unique gravitational waves signal we coined Jet-GWs. These gravitational waves, which are extremely hard to detect, can provide unique information about the engines that power relativistic jets. The project deals with two different aspects of the phenomena: First, constructing a new computational scheme that is capable of calculating the resulting gravitational wave. Second, participating in the design of a Moon-based gravitational radiation detector that will be capable of detecting these Jet-GW signals. (ii) Relativistic jets arise in binary neutron star mergers in particular, the late radio and X-ray observations of the afterglow of the binary merger GW 170817 revealed the existence of such a jet in this world-famous event with the first detection of gravitational waves from a merger by LIGO Virgo this event was followed by more astronomers than any other one so far. The unique observations of GW 170817 revealed a kilonova - the signature of mass ejected from the merger. This mass was composed mostly of rare heavy metals, confirming the idea that mergers are the furnaces in which our universe produces these rare elements, including, for example, gold. Within our project, we explore the propagation of relativistic jets through this matter and the interaction between the two. (iii) Relativistic jets also exist in Supernova. When they emerge from the envelope of the collapsing star, we observe a gamma-ray burst. At times, the jets are choked within the stellar atmosphere and don’t emerge. We explore the conditions for choking and the observational signatures of such choked jets. (iv) A tidal disruption event (TDE) occurs when a star wanders near a supermassive black hole and is shredded to pieces by the enormous gravitational field of the black hole. These events last from a few weeks to a few years. Jets arise in some but not all TDEs. Exploring TDEs, we study the process of jet formation from beginning to end.
We advanced in all four subprogrammes of this project. The work ranges from participation in preparation for a Moon-based gravitational radiation detector to measure Jet-GWs via large-scale simulations of jet propagation and dissipation to analytic modeling.
Our main achievements include the derivation of a novel analytic off-axis relativistic equipartition formalism. Using this formalism, we have demonstrated that even though the emission from relativistic jets is highly beamed along their direction of motion, it is possible that some of the observed TDE jets were observed not along their axis. This explains numerous observational puzzles, such as the emergence of late (a few years) radio flares in some TDEs. It also suggests that TDEs could be the sources of ultra-high-energy cosmic rays, another puzzle in high-energy astrophysics.
Another major achievement was the first-ever long-term simulation of a realistic tidal disruption event. This simulation confirmed that a drastic change of paradigm is needed in the current TDE models. We have also identified a new type of TDE, which we coined “extreme TDEs”. These extreme TDEs occur when a star passes extremely close to a black hole horizon. We have demonstrated that the observational signatures of these TDEs differ drastically from those of regular common TDEs.
As the accretion flow in TDEs is eccentric we carried out the first simulation of magneto-rotational instability in eccentric accretion disk demonstrating the grows of magnetic fields and the resulting effective viscosity.
Finally, we have conducted the first simulation of relativistic jet propagation within a realistic outflow from a binary neutron star merger. This simulation established the conditions for the jets to escape from the outflow and to be collimated by it. We have compared these numerical results to analytic estimates and confirmed their validity. In related simulations, we also obtained the conditions for relativistic jets within supernovae to be choked by the stellar envelopes.
Our main achievements include the derivation of a novel analytic off-axis relativistic equipartition formalism. Using this formalism, we have demonstrated that even though the emission from relativistic jets is highly beamed along their direction of motion, it is possible that some of the observed TDE jets were observed not along their axis. This explains numerous observational puzzles, such as the emergence of late (a few years) radio flares in some TDEs. It also suggests that TDEs could be the sources of ultra-high-energy cosmic rays, another puzzle in high-energy astrophysics.
Another major achievement was the first-ever long-term simulation of a realistic tidal disruption event. This simulation confirmed that a drastic change of paradigm is needed in the current TDE models. We have also identified a new type of TDE, which we coined “extreme TDEs”. These extreme TDEs occur when a star passes extremely close to a black hole horizon. We have demonstrated that the observational signatures of these TDEs differ drastically from those of regular common TDEs.
As the accretion flow in TDEs is eccentric we carried out the first simulation of magneto-rotational instability in eccentric accretion disk demonstrating the grows of magnetic fields and the resulting effective viscosity.
Finally, we have conducted the first simulation of relativistic jet propagation within a realistic outflow from a binary neutron star merger. This simulation established the conditions for the jets to escape from the outflow and to be collimated by it. We have compared these numerical results to analytic estimates and confirmed their validity. In related simulations, we also obtained the conditions for relativistic jets within supernovae to be choked by the stellar envelopes.
The results concerning off-axis relativistic jets, both the derivation of the relevant equipartition formalism and the realization that in some tidal disruption events we have observed such events are clearly beyond the state of art.
The fully relativistic realistic TDE simulations are a second achievement beyond the state of the art. Here, our goal is to go further, including both magnetic fields and radiation in the simulations. This new simulation may challenge our available computation power.
The fully relativistic realistic TDE simulations are a second achievement beyond the state of the art. Here, our goal is to go further, including both magnetic fields and radiation in the simulations. This new simulation may challenge our available computation power.