# Vojtěch Witzany,

personal webpage

Hello, my name is Vojtěch Witzany and I am a physicist working on the theory and phenomenology of black holes. Currently (from Jan 2023), I am a Primus group leader at the Institute of Theoretical Physics at Charles University in Prague. Please enjoy the assortment of links and trivia related to my person below.

## Research

Roughly speaking, much of my research could be summarized as attempting to answer questions such as "How do things behave near black holes? How do they move? How do they evolve?" and, to some degree also "How can we observe all of that?". What these "things" are can vary quite a bit, though. They can be speckles of dust, other black holes, neutron stars, "ordinary" stars, or even clouds of magnetized plasma orbiting the black holes in accretion disks. The fields of the black holes in which the dynamics are happening can be isolated, rotating, non-rotating, but they can also be perturbed by the presence of matter. How we observe it may range from radio dishes on Earth to gravitational-wave detectors and X-ray telescopes in space. To answer all of these questions, I use advanced mathematical techniques and numerical simulations.

## Group

I have been awarded the Primus fellowship by Charles U. in Prague, which allowed me to hire a small team of two postdocs and one PhD student starting from 2023. The team members are:

- Lukáš Polcar (postdoc, started August 2023)

- Viktor Skoupý (postdoc, started October 2023)

- Álvaro Rafael Martínez Gómez (PhD student, started October 2023)

## Study/career track

Masters and Bachellors at Charles University in Prague (2010-2015).

PhD in Theoretical Physics at ZARM, University of Bremen (2015-2018). Received summa cum laude for PhD (exceptional mark for PhD in Germany).

2-year postdoc in the Relativistic Astrophysics group at the Astronomical Institute of the Czech Academy of sciences (2018-2020).

2-year Marie Skłodowska–Curie fellowship at the Relativity group at University College Dublin (2020-2022).

Longer (2+ months) visits at University of Bonn, Max-Planck Institute for Gravitational Physics in Potsdam-Golm, and University of Southampton.

Currently (From January 2023) Primus fellow at the Institute of Theoretical Physics, Charles University, Prague.

Other info in my academic CV (Last updated March '24).

## Outreach writing

I like talking about science from a generalist point of view. I think it brings something to the people who listen but also forces me to take on fresh perspectives.

For a period of time I contributed regularly to Physics Stackexchange (see my profile), I also semi-regularly write popular science articles for the Czech magazine Respekt on various topics:

Velké oko v kosmu (The big eye in space), 3.5. 2015

A retrospective for the 25 years of the Hubble space telescope.Čekání na velký třesk (Waiting for the big bang), 31.5. 2015

Article summarizing the expectations from the second run of LHC.Když v kosmu hřmí (When the cosmic thunder claps), 13.2. 2016

About the announced first measurement of gravitational waves.Na lovu černé tečky (Hunting for the black spot), 20.5. 2017

About the Event Horizon Telescope collaboration and its prospects.Jak vzniká zlato. Vědci zaznamenali srážku dvou neutronových hvězd (Where does gold come from. Scientists have observed a neutron star collision), 16. 10. 2017

On the first announced measurement and observations of the binary neutron star merger.Jak mě Stephen Hawking přivedl k vědě (How Stephen Hawking brought me to science), 14. 3. 2018

A personal story about the impact of Stephen's Hawking Brief History of Time on my life, written on the occasion of Stephen Hawking's death.Na vlnách podivna (On stranger waves), 15.4. 2019

About the announced EHT observations of M87 and their implications.Na dřeň přírodních zákonů (To the hard core of nature), 10.11. 2019

On quantum computing and the implications of the Quantum supremacy claim by GoogleTygr jménem magnetar (The cosmic tiger, magnetar) 15.11. 2020

On the first association of a fast radio burst with a galactic sourceUFO poblíž Chicaga (The UFO near Chicago), 23.5. 2021

Article about the muon magnetic moment anomaly (g-2) announced by Fermilab and its implicationsStín něžného obra (The shadow of the gentle giant), 15.5. 2022

About the first "photo" of the supermassive black hole in the center of our Milky Way Galaxy.

My other miscellaneous outreach writing includes:

Nobelova cena za rok 2020: V centru naší galaxie je cosi temného a těžkého (Nobel Prize 2020: Something dark and heavy lurks in the centre of our galaxy), Pokroky matematiky, fyziky a astronomie 66/4 (2021).

On the half of the 2020 Nobel prize in Physics awarded to Reinhard Genzel and Andrea Ghez for the observations of the galactic centre black holeOd rtuťového podkladu k černým dírám (From a mercury base to black holes), Universum 3/2019, p. 24.

On the history of relativity from the Michelson & Morley experiment to modern observationsSeries of texts about String Theory (2013/14), written in Czech with Miroslav Rapčák for the high-schooler Physics correspondence seminar of the Charles University

Series of texts about dynamical systems and Chaos theory (2014/15), written in Czech for the high-schooler Physics correspondence seminar of the Charles University

Czech translation of the book Black Holes: The Key to Understanding the Universe by Brian Cox and Jeff Forshaw (to be published April 2024 by Vyšehrad/Albatros)

## Scientific publications

You will find my most recent publications by searching me on ArXiv or checking my InspireHEP or Google Scholar profiles.

Here is a list updated in June 2024 (only my 16 published peer-reviewed works are listed in reverse chronological order, conference proceedings and preprints are left out):

Pasham, D. R., et al. (36 authors including Witzany, V.) (2024).

A case for a binary black hole system revealed via quasi-periodic outflows.

Science Advances, 10(13), eadj8898. arXiv:2402.10140

Description: Observations of X-ray flux from galactic center apparently occluded by its outflow. Possible interpretation as an intermediate mass ratio binary of two black holes with the lighter one punching through the accretion disk around the heavier one and launching the outflow. Some support for this scenario from magnetohydrodynamics simulations.Pasham, D.R., Coughlin, E.R., Zajacek, M., Linial, I., Sukova, P., Nixon, C.J., Janiuk, A., Sniegowska, M., Witzany, V., et al. (2024).

Alive but Barely Kicking: News from 3+ years of Swift and XMM-Newton X-ray Monitoring of Quasi-Periodic Eruptions from eRO-QPE1.

Astrophys.J.Lett. 963 (2024) 2, L47

Description: Follow-up observations of one of the handful of known quasi-periodic eruptions in active galactic nuclei. The periods of the eruptions seem to be roughly stable over more than 3 year, while their peak luminosity is gradually declining.Guolo, M., Pasham, D.R., Zajaček, M., Coughlin, E.R., Gezari, S., Suková, P., Wevers, T., Witzany, V., et al. (2024).

X-ray eruptions every 22 days from the nucleus of a nearby galaxy.

Nat. Astron., 1-12. arXiv:2309.03011

Description: Observation and possible interpretations of an X-ray eruption from a nearby galactic center repeating roughly every 22 days. The possibility of a link with the quasi-periodic eruptions occuring on the scale of hours observed in other centers.Witzany, V., & Piovano, G. A. (2024).

Analytic solutions for the motion of spinning particles near spherically symmetric black holes and exotic compact objects.

PRL, 132(17), 171401. arXiv:2308.00021

Description: Separation of variables and integral formulas for the motion of spinning test particles in any static spherically symmetric metric. Fully explicit and worked out formulas for bound motion of spinning test particles near Schwarzschild black holes.Zajaček, M., Czerny, B., Jaiswal, V. K., Štolc, M., Karas, V., Pasham, D. R., Śniegowska, M., Witzany, V., et al. (2023).

Science with a small two-band UV-photometry mission III: Active Galactic Nuclei and nuclear transients.

Space Sci. Rev., Volume 220, Issue 3, article id.29 arXiv:2306.15082

Description: A science white paper about the upcoming Czech space-based UV telescope QUVIK. This paper focuses on transients such as various types of eruptions that one might observe in the centers of galaxies with this telescope.

Polcar, L., Lukes-Gerakopoulos, G., & Witzany, V. (2022).

Extreme mass ratio inspirals into black holes surrounded by matter.

PRD, 106(4), 044069. arXiv:2205.08516

Description: Solution of the orbital dynamics near a Schwarzschild black hole surrounded by an axisymmetric stationary source by the methods of canonical perturbation theory. Inspirals and waveforms using Newtonian fluxes as a toy-model application.Lukes-Gerakopoulos G., Witzany V. (2021).

Nonlinear Effects in EMRI Dynamics and Their Imprints on Gravitational Waves.

In: Bambi C., Katsanevas S., Kokkotas K.D. (eds) Handbook of Gravitational Wave Astronomy. Springer, Singapore. arXiv:2103.06724

Description: A referential chapter on the non-linear transitions that may occur during gravitational-wave inspirals around the so-called resonances.Suková, P., Zajaček, M., Witzany, V., & Karas, V. (2021).

Stellar transits across a magnetized accretion torus as a mechanism for plasmoid ejection.

ApJ 917 43. arXiv:2102.08135

Description: Simulations of a star or a compact object passing through an accretion disk around a black hole. The star's passages through the disk gradually cause the disk to flicker at the same frequency as its orbital frequency. Also, blobs of matter are sometimes launched along the rotation axis of the black hole. All of this is linked to possible existing observations.Zelenka, O., Lukes-Gerakopoulos, G., Witzany, V., & Kopáček, O. (2020).

Growth of resonances and chaos for a spinning test particle in the Schwarzschild background.

Phys. Rev. D, 101(2), 024037. arXiv:1911.00414

Description: Numerical integration of the orbits of spinning bodies near non-rotating black holes. Quantitative analysis of chaos in the motion and the rate at which it emerges. Implies that corresponding gravitational-wave sources for LISA do not require the modelling of chaotic phenomena.Witzany, V. (2019).

Hamilton-Jacobi equation for spinning particles near black holes.

Phys. Rev. D 100.10. arXiv:1903.03651

Description: Breakthrough in the description of spinning bodies near black holes. Problem of motion of spinning body near black hole recast in novel mathematical form and analytically solved.20 authors (Vitor Cardoso and Vojtěch Witzany acting as principal coordinators) (2021).

Probing the nature of black holes: deep in the mHz gravitational-wave sky.

Exp. Astron. 51, 1385–1416. arXiv:1908.11390

Description: A scientific white paper submitted to the ESA Voyage 2050 call. Initiated by the LISA consortium, describes the science case for a technologically superior follow-on mission for the LISA detector.Witzany, V., Steinhoff, J., & Lukes-Gerakopoulos, G. (2019).

Hamiltonians and canonical coordinates for spinning particles in curved space-time.

Class. Quantum Grav. 36 075003. arXiv:1808.06582

Description: An improved theoretical framework for spinning bodies in strong gravitational fields along with a numerical evolution scheme with unprecedented efficiency.Witzany, V., & Jefremow, P. (2018).

New closed analytical solutions for geometrically thick fluid tori around black holes: Numerical evolution and the onset of the magneto-rotational instability.

Astron. Astrophys. 614 (2018): A75. arXiv:1711.09241

Description: New idealized accretion disk solutions that will be used as initial data for astrophysical simulations. Demonstration of properties in a set of numerical simulations.Witzany, V. (2017).

Exploiting the hidden symmetry of spinning black holes: conservation laws and numerical tests.

Mon. Notices Royal Astron. Soc., 473(2), 2434-2440. arXiv:1709.03330

Description: New conservation laws for the evolution of matter near black holes, useful for testing state-of-the-art astrophysical simulations. Demonstration of properties in a numerical study.Markakis, C., Uryu, K., Gourgoulhon, E., Nicolas, J. P., Andersson, N., Pouri, A., & Witzany, V. (2017).

Conservation laws and evolution schemes in geodesic, hydrodynamic, and magnetohydrodynamic flows.

Phys. Rev. D, 96(6), 064019. arXiv:1612.09308

Description: Simplified proofs and derivations of conservation laws for magnetised plasmas in strong gravitational fields. Improved evolution scheme for neutron-star simulations.Witzany, V., & Lämmerzahl, C. (2017).

Pseudo-Newtonian Equations for Evolution of Particles and Fluids in Stationary Space-times.

Astrophys. J., 841(105), 14pp. arXiv:1601.01034

Description: Effective scheme for evolution of accretion disks near black holes within existing Newtonian codes.Witzany, V., Semerák, O., & Suková, P. (2015).

Free motion around black holes with discs or rings: between integrability and chaos–IV.

Mon. Notices Royal Astron. Soc., 451(2), 1770-1794. arXiv:1503.09077

Description: Study of the influence of gravitational perturbations on the motion of bodies near black holes. Comparison with various effective Newtonian models of black holes.