Recent research highlights
Recent research highlights
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Kelvin-Helmholtz threads in 3C84
Unravelling the dynamics of cosmic vortices: Probing a Kelvin-Helmholtz instability in the jet of 3C 84
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Unravelling the dynamics of cosmic vortices: Probing a Kelvin-Helmholtz instability in the jet of 3C 84
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Objectives
Understanding the creation of relativistic jets originating from active galactic nuclei (AGNs) requires a thorough understanding of the accompanying plasma instabilities. Our high-sensitivity, high-resolution, global, very-long-baseline-interferometry observations of the jet in the radio galaxy 3C 84 have enabled us to study its inner morphology.
Results
Results
We find that its thread-like pattern can be described by a Kelvin-Helmholtz instability, consisting of four instability modes. Our model favours a jet described by a Mach number of Mj = 5.0 ±1.7 and a sound speed of αj = 0.14 ±0.06. On this basis, we are able to describe the internal structure of 3C 84 and tentatively connect the origin of the instability to disc accretion activity.
22 GHz observations of 3C 84 in Stokes I and P.
RMHD simulations of the core region of 3C 84.
The spatial scales of relativistic radio jets studied in simulations of jet launching (using relativistic magneto-hydrodynamics, RMHD) and those observed with very long baseline interferometry (VLBI) differ by about ten times. To bridge this gap between simulations and observations, scientists need to focus on nearby active galactic nuclei (AGN), where the jets' parsec-scale regions can be clearly resolved.
Objectives
Objectives
Using 22 GHz globe-spanning VLBI measurements of 3C 84, we studied its sub-parsec region in both total intensity and linear polarization to examine the properties of its jet, achieving a linear resolution of around 0.1 parsec. We tested various simulation setups by changing the bulk Lorentz factor (Γ) of the jet and adjusting the magnetic field configuration (toroidal, poloidal, or helical).
Results
Results
We confirm the presence of a limb-brightened structure extending deep into the sub-parsec region. The electric vector position angles align with the jet flow in the center but tend to be perpendicular near the edges. Our advanced RMHD simulations indicate that this geometry matches a spine-sheath model, featuring a mildly relativistic flow and a toroidal magnetic field configuration.
First EHT observations of 3C84. Image credit: G. F. Paraschos.
AGN jet launching is a long-standing open question in science. High resolution images of the ultimate vicinity of black holes are a unique probe useful in answering this question.
Objectives
Objectives
In this framework we used the first ever EHT observations of the radio galaxy 3C84. In order to gain further insight into the jet physics, we also used linearly polarised light, which is a probe of the magnetic field thought to play a primary role in jet launching.
Results
Results
The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C84.
In this project we aimed to study the long term behaviour of jets, using their total intensity light curves. Such light curves provide insights into the high-energy phenomena associated with jets; for example, flares can be picked up at different wavelenghts and be utilisised to infer the starting point in both space and time.
Objectives
Objectives
Using data from more than four decades, we studied the radio source 3C84 in both radio and γ-rays and compared our results to VLBI data. Our main goals were to investigate whether or not there is an association between patterns in the high and low energy light curves, as well as to estimate the position of the location of the supermassive black hole harboured in this radio galaxy.
Results
Results
Our results are in favour of the γ-ray emission being associated with the radio emission. We are able to tentatively connect the ejection of features identified at 43 and 86 GHz to prominent γ-ray flares. We also computed the multiplicity parameter λ and the Michel magnetisation σM, and find that they are consistent with a jet launched by the Blandford & Znajek mechanism.
A plethora of VLBI data is available for 3C84 and in the past, studies have been conducted to investigate the jet kinematics of its jet. However, at high frequencies this has not been done yet.
Objectives
Objectives
In this work we utilised more than two decades worth of VLBI data to study the kinematics of the 3C84 jet by cross-identifying components at different frequencies and then exploring their movement in time. As a by-product of our analysis of the multiple epochs, we were also able to investigate the jet morphology.
Results
Results
We determined the kinematics of the inner jet and ejected features at 43 and 86 GHz and compared their ejection times with radio and γ-ray variability. For the moving jet features, we found an average velocity of β = 0.055−0.22c (μ = 0.04 − 0.18 mas/yr). From the time-averaged VLBI images at the three frequencies, we measured the transverse jet width along the bulk flow. On the ≤1.5 parsec scale, we found a clear trend of the jet width being frequency dependent, with the jet being narrower at higher frequencies. From quasi-simultaneous observations at 43 and 86 GHz, we obtain spectral index maps, revealing a time-variable orientation of the spectral index gradient due to structural variability of the inner jet.
3C84/NGC1275 is a well studied radio galaxy in different branches of astronomy. However, it still remains unclear where exactly the central engine, powering the massive jets launched at its nucleus, is located. This has implications with regard to the magnetic field strength and geometry.
Objectives
Objectives
We set out to pinpoint the exact location of the central, supermassive black hole in 3C84 by using quasi-simultaneously observed radio data of the source at three different frequencies.
Results
Results
We found the jet apex to be located 83 ± 7 μas north (upstream) of the 86 GHz VLBI core. We also found a mixed toroidal-poloidal magnetic field configuration, consistent with a region that is offset from the central engine by about 400-1500 Rs. The measured core shift is then used to estimate the magnetic field strength, which amounts to B = 1.80−4.0 G near the 86 GHz VLBI core.
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