Dr James Matthews
Astrophysicist
The movies below are from the paper,
"Ultra-high energy cosmic rays from shocks in the lobes of radio galaxies",
which can be viewed on arXiv.
The abstract is below. A number of companion papers have also been published, including the following studies:
Matthews et al. 2018 suggest that Fornax A and Centaurus A can explain Auger cosmic ray data.
Bell et al. 2019 introduce a theoretical model for acceleration by weak shocks in a backflow or `flux tube'.
Matthews et al. 2020 provide a review of particle acceleration in astrophysical jets.
Abstract: The origin of ultra-high energy cosmic rays (UHECRs) has been
an open question for decades. Here, we use a combination of
hydrodynamic simulations and general physical arguments
to demonstrate that UHECRs can in principle be produced by
diffusive shock acceleration (DSA) in shocks in the backflowing
material of radio galaxy lobes. These shocks occur
after the jet material has passed through the relativistic
termination shock. Recently, several authors have demonstrated that
highly relativistic shocks are not effective in accelerating UHECRs.
The shocks in our proposed model have a range of non-relativistic or mildly relativistic shock velocities more conducive to UHECR acceleration, with shock sizes in the range 1-10 kpc.
Approximately 10% of the jet's energy flux is focused through
a shock in the backflow of M>3.
Although the shock velocities can be
low enough that acceleration to high energy via DSA is still
efficient, they are also high enough for the Hillas energy to approach
10-100 EeV, particularly for heavier CR composition and
in cases where fluid elements pass through
multiple shocks. We discuss some of the more general considerations
for acceleration of particles to ultra-high energy with reference
to giant-lobed radio galaxies such as Centaurus A and Fornax A,
a class of sources which may be responsible for the
observed anisotropies from UHECR observatories.
These movies are referenced in the text of the above paper (published MNRAS) and
show how supersonic backflows can form in an AGN jet.
james.matthews [at] physics [dot] ox [dot] ac [dot] uk
Oxford Astrophysics
The Denys Wilkinson Building,
Keble Road,
Oxford
OX1 3RH
Volume rendering of the fiducial fast 3D simulation, F3D, showing v_z, the vertical component of velocity. The opacity is set linearly by the jet tracer. Click on the blue filename above to download/open the file.
Volume rendering of the fiducial fast 3D simulation, F3D, showing the Mach number. The opacity is set linearly by the kinetic energy flux. Click on the blue filename above to download/open the file.
Logarithm of Mach number and vertical velocity for a snapshot of the S1 2D simulation. In the v_z plot, compression structures (div(v)< 0) are coloured in grey to indicate shocks. Supersonic backflows form in both simulations and vortex shedding occurs from the jet head. Click on the blue filename above to download/open the file.
Logarithm of Mach number and vertical velocity for a snapshot of the F1 2D simulation. In the v_z plot, compression structures (div(v)< 0) are coloured in grey to indicate shocks. Supersonic backflows form in both simulations and vortex shedding occurs from the jet head. Click on the blue filename above to download/open the file.
Github
ORCID