Simulation reveals secrets of dancing jets in Twin Radio Galaxy TRG J104454+354055 in deep space
Santanu Mondal
Most of the galaxies observed to date are believed to host SMBH at the centre (Kormendy & Richstone 1995), whose evolution over time occurs through accreting matter from their surrounding environment, primarily from their host galaxy, forming an accretion disk around them. During their active accretion phase, they also throw some fraction of the accreted matter out in the form of jets, which consist of hot plasma accumulated through accretion. These jets are emitted along the spinning axis of the SMBH, above and below the plane of the accretion disk. The jets propagate through their ambient medium, which can be the intergalactic or intracluster medium, and can extend over a distance of a few million light years, as observed so far. The medium through which jets are drilling has a density much higher compared to the jet itself. As a result, the low-density jets need to fight against the high-density medium during propagation, which leaves imprints in their structure. Our understanding of large-scale radio jets in merger systems has been drastically improved in the era of the Very Large Array, Very Long Baseline Array/European VLBI Network, upgraded Giant Metrewave Radio Telescope, and MeerKAT.
The SMBH can also evolve through a sequence of merging processes of the host galaxy with another galaxy (Kormendy & Ho 2013). During this merging process, it is expected that the SMBHs in each host will gradually sink toward each other in their orbits due to stellar dynamical friction and/or energy dissipation caused by their circumnuclear gas, ultimately forming a binary or a dual-SMBH system (Rodriguez et al. 2006, Burke-Spolaor et al. 2014). When the approaching active SMBHs are separated by relatively small (<100 pc) distances, they are referred to as binary SMBH; when still separated by kpc scale distance, they are called dual SMBH. In both cases, jets may or may not be emitted always.
However, in TRGs both SMBHs emit twin bipolar jets. So far only three such systems have been discovered and confirmed. The third one, TRG J104454+354055 located in deep space at a few billion light-years away from us, has recently been discovered using data from India’s upgraded Giant Metrewave Radio Telescope (uGMRT). In this TRG, both radio jets are discernible up to 100 kiloparsec scale, and the overall radio structure spans 400 kiloparsec, along with clear helical and bending structures. The two SMBHs are separated by around 30 kpc. The present-day image of the system shows that both bipolar jets are well separated and propagating in parallel with helical morphology without any interaction among them. These features in their structure make them more interesting and a cleaner test-bed to study such complex and rare systems. Despite their clean morphology, we hardly know about the physical reason behind their observed appearance and underlying origin.
A team of astronomers led by Dr. Santanu Mondal, a Ramanujan Fellow at the Indian Institute of Astrophysics (IIA), along with Dr. Ravi Joshi (IIA), Dr. Gourab Giri (now at INAF-IRA Bologna), Profs. Paul Wiita (The college of New Jersey, USA), Gopal-Krishna (UM-DAE Centre for Excellence in Basic Sciences, India), and Luis C. Ho (Peking University, China) initiated a program of computer simulation modeling to decipher the origin of the observed morphology in TRG J104454+354055 (Mondal et al. 2025). We performed extensive and robust hydrodynamic simulations in 3D for different environments. These simulations included precession effects in both tilted low-velocity bipolar jets and examined the possible outcomes, whether they can generate the observed structures or not.
We found that the computer simulation with precession period of 20-50 Myr can explain the observed morphology satisfactorily. Additionally, simulations revealed that the movement of both jets is more or less steady in the vertical direction (y-axis) and more dancing in nature in the lateral direction (x-axis), which is mostly due to the dynamics and precession effects. The left panel of Fig. 1 shows the color-coded uGMRT image of the TRG system, and the right panel shows the simulated ones. The observed bends and lobes have been clearly reproduced by the computer simulation. Our results further imply that the jets without precession cannot produce the morphology observed in this TRG. We have established that the precession is effective even when two SMBHs or their jets are separated by a million light years. As a deeper understanding of the jet launching, this study answers the following question: What can be the origin of such precession required to explain the observation? The matter which is accreted by the central SMBH is rotating, hence, carries angular momentum, and the SMBH is also spinning with some angular momentum. When the spin axis is misaligned with the angular momentum, they produce a torque (Bardeen & Petterson 1975), which can end up forming precession in jets. These kinds of studies are crucial in understanding the connection between accretion and jet, reshaping of jets during their propagation, and the effect of the surrounding medium.
In summary, this work simulates two bipolar sub-relativistic, tilted precessing jets from two SMBHs in a merger system, TRG J104454+354055, for the first time to understand the origin of their observed morphologies. This approach to understanding TRG jet dynamics could also be applied to other similar TRG systems that may be discovered in the era of high resolution telescopes and big surveys. This result has been published in the Astrophysical Journal.
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Figure 1. Left panel: The color-coded uGMRT image of TRG J104454+354055 at 1.4 GHz (Gopal-Krishna et al. 2022). Right panel: Simulated normalized synchrotron intensity map of the TRG at 1.4 GHz. Different structures (bends, lobes, and plumes) are marked with the image. Figures are adapted from Mondal et al. 2025.
References:
1. Gopal-Krishna, Joshi, R., Patra, D., et al. 2022, MNRAS, 514, L36
2. Mondal, S., Giri, G., Joshi, R., et al. 2025, ApJ, 987, 162
3. Kormendy, J., & Ho, L. C. 2013, ARA&A, 51, 511
4. Kormendy, J., & Richstone, D. 1995, ARA&A, 33, 581
5. Bardeen, J. M., & Petterson, J. A. 1975, ApJL, 195, L65
Link to the published paper:
Santanu Mondal et al. ApJ, 2025, 987, 162
Contact:
Santanu Mondal, Indian Institute of Astrophysics, India. Email: santanuicsp@gmail.com