BHAC released

With great please I can finally announce the release of BHAC v1.0 under the GPL3 license! You can find usage instructions and updated documentation at our new website bhac.science.

I'm really looking forward to the science coming out of the public code!


29th Nov 2019 by Oliver
tags: bhac

Accretion

By studying accretion and outflows from compact objects, we learn about the most efficient energy source in the universe. I'm particularly interested in the formation, collimation and ultimately dissipation of relativistic jets which emanate from the direct vicinity of black holes across all mass ranges.

One of the most exciting observations in this field was the recent imaging of the black hole in the galaxy M87. Using Very Long Baseline Interferometry (VLBI) of high-frequency radio telescopes scattered across the globe, the Event Horizon Telescope Collaboration took this image.

Image credit: EHTC, CC BY-ND 4.0

Numerical simulations of turbulent accretion (with bhac among other codes) were combined with general relativistic ray-tracing to interpret the structure seen on the image: we witness the light emitted from hot plasma on its final orbits before plunging into the black hole. The dark region in the center is the so-called black hole shadow, a gravitationally lensed projection of the unstable photon orbit. Within the shadow area all light vanishes within the event horizon.

The galaxy M87 is also famous for its remarkable relativistic jet which is one of the best studied in astrophysics. Using high resolution 3D adaptive mesh refinement simulations with bhac, we have modeled the launching of the jet with unprecedented accuracy. Modeling the electrons within a kappa-distribution, we find that non-thermal particles are crucial to extend the spectrum beyond the radio band.

Relativistic ray-traced images of the simulated jet at three different radio frequencies: 43GHz (left), 86GHz (middle) and the EHT frequency of 230GHz (right). See the paper led by Jordy Davelaar for details.


17th Jun 2019; last edit 1st Sep 2019 by Oliver
tags: website, accretion

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Relativistic plasma dynamics

Accretion

With numerical simulations of accreting compact objects, we study the transport of angular momentum and magnetic field, the ejection of relativistic jets and model horizon scale structure observed by the Event Horizon Telescope.

Pulsar Wind Nebulae

PWN are unique laboratories to investigate relativistic plasma. Among other things, they teach us about fluid instabilities, relativistic shocks, magnetic dissipation, particle acceleration and turbulent processes.

Radiative signatures

By modeling the non-thermal radiation emitted from astrophysical plasma, we extract important source parameters and understand particle energetization in a regime impossible to study in the laboratory.

Computational methods

The main tools of my research

Black Hole Accretion Code [BHAC]

Build upon the MPI-AMRVAC framework, the Black Hole Accretion Code solves the equations of general relativistic magnetohydrodynamics (GRMHD). Its modular design allows to simulate not only Einstein gravity, but also Black Holes in arbitrary metric theories of gravity and other compact objects. BHAC is the workhorse GRMHD-code for the blackholecam collaboration and provides source models for the Event Horizon Telescope Collaboration.

Adaptive Mesh Refinement Versatile Advection Code [MPI-AMRVAC]

With a current focus on solar- and non-relativistic astrophysical applications, MPI-AMRVAC offers a wide range of advanced features for the solution of (quasi-) conservation laws. Adaptive grids can be employed in cartesian, cylindrical and (stretched) spherical geometries. The code has been modernized recently and the documentation is frequently updated.