About Me

Since September 2022 I am a postdoctoral researcher in the Astrophysical and Cosmological Relativity group of Alessandra Buonanno at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) in Potsdam, Germany. Before that I was a postdoctoral researcher in the ERC group of Enrico Barausse at SISSA and IFPU in Trieste, Italy. Until November 2019 I was a Phd student in the Theoretical Astrophysics group of Kostas D. Kokkotas at the University of Tübingen in Germany.

My studies are on Albert Einstein's legacy of general relativity and its fascinating implications for astrophysics and fundamental physics. Since the groundbreaking detections of gravitational waves from binary black hole and neutron star mergers, we are entering a new era of physics and hopefully find new unexpected aspects of nature that wait to be explored!

More information about me and my research can be found on this website, as well as in this podcast.

E-Mail

About my Research

In simple words

The main focus of my research is on the characteristic oscillation modes of compact objects, such as neutron stars and black holes. Different compact objects have different spectra and similar to atom spectroscopy or seismic studies of Earth, one can potentially learn a lot about the objects from the knowledge and correct interpretation of their spectrum. While theoretical studies of gravitational wave emission have been investigated for a long time, observational access to gravitational waves is a recent and revolutionary progress in physics. My specific line of research is on the question about how the knowledge of characteristic oscillation modes can be used to reconstruct properties of the source, thus to solve the inverse problem. With further improvements of gravitational wave observatories, the spectroscopy of compact objects is in reach soon. Recently I have been working on using the shadow of black holes to test general relativity and studied rotating neutron stars from their characteristic oscillations. An explanation of my research and the one of the Max Planck Institute for Gravitational Physics can also be found in this podcast.

A little bit more technical

In most of my works I have studied the quasi-normal mode spectrum of compact objects, including neutron stars [6], models of ultra compact alternatives [1,2,5], and black hole space-times beyond general relativity [8]. These works are all within perturbation theory. In order to address the inverse quasi-normal mode problem, I have explored semi-analytic methods, such as WKB, to constrain the perturbation potentials and case dependent also parts of the metric and other properties of the objects. Furthermore I have conducted research projects on gravitational wave parameter estimation [3], Hawking radiation [7] and black hole area quantization [9,15]. Currently I am extending the inverse spectrum methods to address more complex systems and work on gravitational wave parameter estimation using Bayesian analysis [10,16,18]. I have also been working on using the shadow of the supermassive black holes to test strong-field general relativity [11,14]. Recent work includes Bayesian inference to relate neutron star oscillations with their parameters [13,17,23]. After moving to the Albert Einstein Institute, I started working on analyzing the black hole ringdown overtone problem [21] and advanced techniques for the computation of quasi-normal [19,20,22].

Latest News

2023

01 Dec
Phys. Rev. D accepted our paper on The Inverse Problem of Analog Gravity Systems for publication.
30 Nov
Phys. Rev. D accepted our paper on Rapidly rotating neutron stars: Universal relations and EOS inference for publication.
09 Nov
Gave a talk at the Galaxy Coffee, Max Planck Institute for Astronomy, Heidelberg, Germany.
07 Nov
Gave a talk at the Astrocoffee, Goethe University Frankfurt, Germany.
11 Oct
Gave a talk at the workshop on Nonlinear Aspects of General Relativity, Princeton University, USA.
05 Oct
Gave a seminar for the group of Emanuele Berti at Johns Hopkins University, USA.
07 Sep
Gave a talk at the XXV SIGRAV Conference, Trieste, Italy.
16 Aug
Phys. Rev. D published our paper on Role of black hole quasinormal mode overtones for ringdown analysis.
19 Jul
Gave a talk at the Amaldi15: Premier International Conference on Gravitational Waves (online).
17 Jul
Phys. Rev. D published our paper on Quasi-normal modes of non-separable perturbation equations: the scalar non-Kerr case.
14 Jul
I recorded a podcast on our research at the Max Planck Institute for Gravitational Physics.
12 Jul
Gave a talk for the Einstein Seminar of the Theoretical Astrophysics Group at the University of Tübingen, Germany.
30 Jun
Phys. Rev. D published our paper on A parametrized quasi-normal mode framework for non-Schwarzschild metrics.
29 Jun
Gave an invited talk at the DPG-Lehrerfortbildung on gravitational waves in Bad Honnef, Germany.
14-16 Jun
Organized the workshop Connecting the dots: Toward inspiral-merger-ringdown gravitational waveforms beyond general relativity, AEI Potsdam, Germany.
17 May
Participated at the outreach event „Universe on Tour – Licht aus! Sterne an!“, Luisenplatz Potsdam, Germany.
10 May
Participated at the outreach event for members of the German Bundestag on the ship MS Wissenschaft, Berlin, Germany.
06 May
Participated at the Potsdamer Tag der Wissenschaften/Potsdam Science Day.
22 Mar
Gave a talk at the DPG Spring Meeting of the Matter and Cosmos Section (SMuK) in Dresden.
15 Feb
Our new article: To ring or not to ring, the tale of black hole quasi-normal modes has been submitted.
28 Jan
Our proposal to the Gravity Theory Trust to organize a workshop at the AEI has been approved.

Curriculum Vitae

Academic Track Record

Postdoc
2022-now, Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Potsdam, Germany
Postdoc
2019-2022, SISSA and IFPU, Trieste, Italy
PhD Stud.
2017-2019, University of Tübingen, Germany
MSc Stud.
2015-2016, University of Tübingen, Germany
BSc Stud.
2011-2015, University of Tübingen, Germany

PhD Thesis

Title
On the Gravitational Wave Spectrum of Compact Relativistic Objects
Institution
University of Tübingen, Germany
Superv.
Prof. Dr. Kostas D. Kokkotas and Prof. Dr. Wilhelm Kley
Ext. Exam.
Prof. Dr. Emanuele Berti (Johns Hopkins University, USA)
Grade
summa cum laude

Awards/Mentions

Received the Promotionspreis of the University of Tübingen 2021
Selected for finals of DPG Section Matter and Cosmos Dissertation Prize 2021
Honorable mention for GWIC-Braccini Thesis Prize 2020

Link to published thesis, submitted 2019, accepted 2020

Publications

Overview in INSPIRE and ORCID.


Regular Articles

[24]
The Inverse Problem of Analog Gravity Systems
Saulo Albuquerque, Sebastian H. Völkel, Kostas D. Kokkotas and Valdir B. Bezerra
accepted for publication in Phys. Rev. D
Link to arxiv
[23]
Rapidly rotating neutron stars: Universal relations and EOS inference
Christian J. Krüger and Sebastian H. Völkel
accepted for publication in Phys. Rev. D
Link to arxivand journal
[22]
Quasi-normal modes of non-separable perturbation equations: the scalar non-Kerr case
Rajes Ghosh, Nicola Franchini, Sebastian H. Völkel and Enrico Barausse
Phys. Rev. D 108, 024038, 2023
Link to arxiv and journal
[21]
Role of black hole quasinormal mode overtones for ringdown analysis
Peter James Nee, Sebastian H. Völkel and Harald P. Pfeiffer
Phys. Rev. D 108, 044032, 2023
Link to arxiv and journal
[20]
A parametrized quasi-normal mode framework for non-Schwarzschild metrics
Nicola Franchini and Sebastian H. Völkel
Phys. Rev. D 107, 124063, 2023
Link to arxiv and journal
[19]
Quasi-Normal Modes from Bound States: The Numerical Approach
Sebastian H. Völkel
Phys. Rev. D 106, 124009, 2022
Link to arxiv and journal
[18]
Constraining modifications of black hole perturbation potentials near the light ring with quasinormal modes
Sebastian H. Völkel, Nicola Franchini, Enrico Barausse and Emanuele Berti
Phys. Rev. D 106, 124036, 2022
Link to arxiv and journal
[17]
Constraining the Nuclear Equation of State from Rotating Neutron Stars
Sebastian H. Völkel and Christian J. Krüger
Phys. Rev. D 105, 124071, 2022
Link to arxiv and journal
[16]
Theory-agnostic Reconstruction of Potential and Couplings from Quasi-Normal Modes
Sebastian H. Völkel, Nicola Franchini and Enrico Barausse
Phys. Rev. D 105, 084046, 2022
Link to arxiv and journal
[15]
On Black Hole Area Quantization and Echoes
Andrew Coates, Sebastian H. Völkel, and Kostas D. Kokkotas
Class. Quantum Grav., 39 045007, 2022
Link to arxiv and journal
[14]
Separating Astrophysics and Geometry in Black Hole Images
Guillermo Lara, Sebastian H. Völkel, and Enrico Barausse
Phys. Rev. D 104, 124041, 2021
Link to arxiv and journal
[13]
Bayesian inverse problem of rotating neutron stars
Sebastian H. Völkel, Christian J. Krüger and Kostas D. Kokkotas
Phys. Rev. D 103, 083008, 2021
Link to arxiv and journal
[12]
An exact theory for the Rezzolla-Zhidenko metric and self-consistent calculation of quasi-normal modes
Arthur G. Suvorov and Sebastian H. Völkel
Phys. Rev. D 103, 044027, 2021
Link to arxiv and journal
[11]
EHT tests of the strong-field regime of General Relativity
Sebastian H. Völkel, Enrico Barausse, Nicola Franchini and Avery E. Broderick
Class. Quantum Grav. 38, 21LT01, 2021
Link to arxiv and journal
[10]
Bayesian Metric Reconstruction with Gravitational Wave Observations
Sebastian H. Völkel and Enrico Barausse
Phys. Rev. D 102, 084025, 2020
Link to arxiv and journal
[9]
Spectral lines of quantized, spinning black holes and their astrophysical relevance
Andrew Coates, Sebastian H. Völkel and Kostas D. Kokkotas
Phys. Rev. Lett. 123, 171104, 2019
Link to arxiv and journal
[8]
Scalar fields and parametrized spherically symmetric black holes: Can one hear the shape of space-time?
Sebastian H. Völkel and Kostas D. Kokkotas
Phys. Rev. D 100, 044026, 2019
Link to arxiv and journal
[7]
The Inverse Problem for Hawking Radiation
Sebastian H. Völkel, Roman Konoplya and Kostas D. Kokkotas
Phys. Rev. D 99, 104025, 2019
Link to arxiv and journal
[6]
On the Inverse Spectrum Problem of Neutron Stars
Sebastian H. Völkel and Kostas D. Kokkotas
Classical and Quantum Gravity 36, 115002, 2019
Link to arxiv and journal
[5]
Wormhole Potentials and Throats from Quasi-Normal Modes
Sebastian H. Völkel and Kostas D. Kokkotas
Classical and Quantum Gravity 35, 105018, 2018
Link to arxiv and journal
[4]
Inverse spectrum problem for quasi-stationary states
Sebastian H. Völkel
Journal of Physics Communications 2, 025029, 2018
Link to arxiv and journal
[3]
Parameter estimation of gravitational wave echoes from exotic compact objects
Andrea Maselli, Sebastian H. Völkel and Kostas D. Kokkotas
Phys. Rev. D 96, 064045, 2017
Link to arxiv and journal
[2]
Ultra Compact Stars: Reconstructing the Perturbation Potential
Sebastian H. Völkel and Kostas D. Kokkotas
Classical and Quantum Gravity 34, 175015, 2017
Link to arxiv and journal
[1]
A Semi-analytic Study of Axial Perturbations of Ultra Compact Stars
Sebastian H. Völkel and Kostas D. Kokkotas
Classical and Quantum Gravity 34, 125006, 2017
Link to arxiv and journal

Reviews

[R.2]
Testing General Relativity with Black Hole Quasi-Normal Modes
Nicola Franchini and Sebastian H. Völkel,
Invited chapter for the book "Recent Progress on Gravity Tests"
(Editors Cosimo Bambi and Alejandro Cárdenas-Avendaño, Springer Singapore, expected in 2023)
Link to arxiv
[R.1]
Fast Rotating Neutron Stars: Oscillations and Instabilities
Christian J. Krüger, Kostas D. Kokkotas, Praveen Manoharan and Sebastian H. Völkel,
Front. Astron. Space Sci. 8, 166, 2021
Link to arxiv and journal

Proceedings

[Pr.1]
Hearing the Nature of Compact Objects
Sebastian H. Völkel and Kostas D. Kokkotas
Einstein Equations: Physical and Mathematical Aspects of General Relativity. DOMOSCHOOL 2018
Link to the proceedings

Multi-author

[Ma.1]
Prospects for Fundamental Physics with LISA
Enrico Barausse et al.
Gen. Rel. Grav. 52, 81, 2020
Link to the journal

Outreach and Others

[OP.4]
EHT tests of the strong-field regime of General Relativity
Sebastian H. Völkel and Nicola Franchini
ERC GRAMS blog, October 13, 2021
Link to the blog
[OP.3]
69. Lindau Nobel Laureate Meeting
Victoria Grinberg, Olaf Kramer, Christian Strandhagen, Sebastian H. Völkel
attempto online, 24.07.2019
Link to the blog
[OP.2]
The Sound of Exotic Astrophysical "Instruments"
Sebastian H. Völkel and Kostas D. Kokkotas
CQG+, May 28, 2018
Link to the blog
[OP.1]
Can one hear the shape of an ultra compact object?
Sebastian H. Völkel and Kostas D. Kokkotas
CQG+, October 2, 2017
Link to the blog

Talks and Posters

Invited Talks, Seminars and Colloquia

[ST.18]
Max Planck Institute for Astronomy
Galaxy coffee
09. November 2023, Heidelberg, Germany
[ST.17]
Goethe University Frankfurt
Astrocoffee
07. November 2023, Frankfurt, Germany
[ST.16]
Johns Hopkins University
Group of Emanuele Berti
06. October 2023, Baltimore, USA
[ST.15]
University of Tübingen
Einstein Seminar
12. July 2023, Tübingen, Germany
[ST.14]
DPG Physikzentrum
Lehrerfortbildung zu Gravitationswellen
29. June 2023, Bad Honnef, Germany
[ST.13]
INFN TEONGRAV
monthly online seminar
28. April 2022, Italy (online)
[ST.12]
Fudan University
Group of Cosimo Bambi
29. March 2022, China (online)
[ST.11]
University of Illinois at Urbana-Champaign
Group of Nicolas Yunes
23. March 2022, USA (online)
[ST.10]
Perimeter Institute for Theoretical Physics
Strong Gravity Seminar
24. February 2022, Waterloo, Canada (online)
[ST.9]
University of Tübingen
Theoretical Astrophysics Tübingen
18. Novemer 2021, Tübingen, Germany (hybrid)
[ST.8]
DPG Section Matter and Cosmos Meeting 2021
Dissertation Prize Symposium
30. August 2021, Jena, Germany (remotely)
[ST.7]
University of Tübingen
Mathematical Physics Colloquium
07. July 2021, Tübingen, Germany (remotely)
[ST.6]
Sapienza University of Rome
Virtual Gravity seminar
19. October 2020, Rome, Italy, (remotely)
[ST.5]
Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
ACR seminar
30. September 2020, Potsdam, Germany, (remotely)
[ST.4]
Institut d'Astrophysique de Paris (IAP)
GReCO seminar
28. September 2020, Paris, France, (remotely)
[ST.3]
University of Tübingen
Theoretical Astrophysics Tübingen
09. July 2020, Tübingen, Germany, (remotely)
[ST.2]
Goethe University Frankfurt and Frankfurt Institute for Advanced Studies
AstroCoffee
07. July 2020, Frankfurt, Germany, (remotely)
[ST.1]
University of Southampton
Gravity seminar
30. April 2020, Southampton, United Kingdom, (remotely)

Contributions to Conferences, Workshops and Schools

[T.24]
Confronting black hole spectroscopy with the ringdown
Presented my work at Nonlinear Aspects of General Relativity
11. October 2023, Princeton University, USA.
[T.23]
Constraining modifications of black hole perturbation potentials near the light ring with quasinormal modes
Presented my work at XXV SIGRAV Conference
07. September 2023, Trieste, Italy.
[T.22]
Constraining modifications of black hole perturbation potentials near the light ring with quasinormal modes
Presented my work at Amaldi15: Premier International Conference on Gravitational Waves
19. July 2023, (online).
[T.21]
Constraining modifications of black hole perturbation potentials near the light ring with quasinormal modes
Presented my work at the DPG Spring Meeting of the Matter and Cosmos Section (SMuK)
23. Mar 2023, Technical University Dresden, Germany.
[T.20]
Probing Black Holes with Quasi-Normal Modes
Presented my work at the INFN TEONGRAV annual meeting
22. July 2022, Arcetri, Florence, Italy (remotely).
[T.19]
Constraining the Nuclear Equation of State from Rotating Neutron Stars
Presented my work at the ECT* Workshop: Neutron stars as multi-messenger laboratories for dense matter
20. June 2022, ECT*, Villa Tambosi, Trento, Italy.
[T.18]
Probing Black Holes with Quasi-Normal Modes
Presented my work at the EuCAPT Workshop: Gravitational wave probes of black hole environments
17. June 2022, Sapienza University of Rome, Italy.
[T.17]
Probing Black Holes with Quasi-Normal Modes and Shadows
Presented my work at Atlantic General Relativity 2022 (1st prize)
19. May 2022, Memorial University of Newfoundland and Labrador, Canada (remotely).
[T.16]
Constraining black holes with quasi-normal modes
Presented my work at the 31st Midwest Relativity Meeting
11. Nov 2021, University of Illinois in Urbana-Champaign, USA (remotely)
[T.15]
Reconstructing black hole metrics with gravitational waves and shadows
Presented my work at the 14th Edoardo Amaldi Conference on Gravitational Waves
22. Jul 2021, Australia (remotely)
[T.14]
Metric reconstruction with gravitational waves and shadows
Presented my work at the Meeting of the National Research Group on Gravitational Waves
01. Apr 2021, Paris, France (remotely)
[T.13]
Metric reconstruction with gravitational waves and shadows
Presented my work at the INFN TEONGRAV Workshop 2021
18. Feb 2021, Italy (remotely)
[T.12]
Metric reconstruction with gravitational waves and shadows
Presented my work at the XIII Black Holes Workshop
21. Dec 2020, Lisbon, Portugal (remotely)
[T.11]
Master Class of Brian P. Schmidt
Presented my field at the "69th Lindau Nobel Laureate Meeting"
03. July 2019, Lindau, Germany
[T.10]
Hearing the Nature of Compact Objects
Presented my research at Gravitational Waves, Black Holes and Fundamental Physics
23. January 2019, Athens, Greece
[T.9]
Probing the Nature of Compact Objects with QNMs
Overview talk at the 3rd HEL.A.S. SUMMER SCHOOL AND DAAD SCHOOL
08. October 2018, Thessaloniki, Greece
[T.8]
The Sound of Relativistic Objects
Overview talk at the Kepler Center PhD Workshop 2018
26 September 2018, Obermarchtal, Germany
[T.7]
Probing the Nature of Compact Objects with QNMs
Presented my research at NEB18
21 September 2018, Rhodes, Greece
[T.6]
Hearing the Nature of Compact Objects
Presented my research at Domoschool 2018
19 July 2018, Domodossola, Italy
[T.5]
From Compact Objects to Quasi-Normal Modes and Back
Presentation of my current research at the X Black Holes Workshop
18 December 2017, Aveiro, Portugal
[T.4]
Exotic Compact Objects
Lecture for the DAAD Winter School: Neutron Stars in the Era of Gravitational Waves
30 November 2017, Thessaloniki, Greece
[T.3]
From Compact Objects to Quasi-Normal Modes and Back
General talk about my current research status at the University's Kepler PhD Workshop
29 September 2017, Freudenstadt-Lauterbad, Germany
[T.2]
From Compact Objects to Quasi-Normal Modes and Back
Presentation of my research papers [1-3] at the 9th Aegean Summer School
22 September 2017, Sifnos, Greece
[T.1]
Gravitational Waves from Compact Objects
General talk about my Master thesis at the University's Kepler PhD Workshop
5 October 2016, Freudenstadt-Lauterbad, Germany

Outreach Activities

[O.8]
I recorded a podcast on our research at the Max Planck Institute for Gravitational Physics.
2023, Germany
[O.7]
„Universe on Tour – Licht aus! Sterne an!“
Explained the research carried out at the Albert Einstein Instiute to the public.
17 May 2023, Luisenplatz Potsdam, Germany
[O.6]
MS Wissenschaft
Outreach event for members of the German Bundestag.
10 May 2023, MS Wissenschaft Berlin, Germany
[O.5]
Potsdamer Tag der Wissenschaften/Potsdam Science Day
Explained the research carried out at the Albert Einstein Instiute to the public.
06 May 2023, University of Potsdam, Germany
[O.4]
Open door day of the Potsdam Science Park
Explained the research carried out at the Albert Einstein Instiute to the public.
03 September 2022, Albert Einstein Instiute, Potsdam, Germany
[O.3]
Gravitationswellen und kompakte Objekte: Einsteins kosmisches Orchester
Invited talk at the Arbeitskreis Astronomie
08 January 2020, University of Stuttgart, Germany
[O.2]
The Sound of Black Holes
My contribution to the Science Slam at the Doctoral Candidates’ Convention
21 February 2018, University of Tübingen, Germany
[O.1]
Gravitationswellen von kompakten Objekten
General poster about my research at the open day of the Institute for Astronomy and Astrophysics
04 November 2017, Tübingen, Germany

Posters

[P.4]
Metric Reconstruction with Gravitational Waves and Shadows
On recent publications [10, 11] at the workshop Gravitational Waves: a new messenger to explore the universe
01 -- 12 Mar 2021, Paris, France (online)
[P.3]
Metric Reconstruction with Gravitational Waves and Shadows
On recent publications [10, 11] at the 740. WE-Heraeus-Seminar: Experimental Tests and Signatures of Modified and Quantum Gravity
01 February 2021, Bad Honnef, Germany (online)
[P.2]
From Compact Objects to Quasi-Normal Modes and Back
Presentation of my current status of research at the NewCompStar School 2017
14 September 2017, Sofia, Bulgaria
[P.1]
From Compact Objects to Quasi-Normal Modes and Back
Presentation of my current status of research at the 641. WE-Heraeus-Seminar: Do Black Holes Exist? - The Physics and Philosophy of Black Holes
25 April 2017, Bad Honnef, Germany

Work as Referee

I worked as referee for the following journals:

Physical Review Letters
Physical Review D
Journal of Cosmology and Astroparticle Physics (JCAP)
General Relativity and Gravitation
International Journal of Modern Physics D
The European Physical Journal C
The European Physical Journal Plus
Universe
Galaxies

Teaching

I gave lectures about:

SS19
Gravitational Waves in Cosmology
Additional hours (2x90 minutes) for the Observational Cosmology lecture
University of Tübingen, Germany

I worked as tutor to discuss weekly exercises with a class of students for the following lectures:

WS17/18
Theoretical Mechanics and Introduction to Quantum Mechanics
University of Tübingen, Germany
SS17
Electromagnetism
University of Tübingen, Germany
SS16
Observational Cosmology
University of Tübingen, Germany
SS15
Observational Cosmology
University of Tübingen, Germany

Organizing workshops and conferences

14-16 Jun 2023
Connecting the dots Toward inspiral-merger-ringdown gravitational waveforms beyond general relativity
Part of organizing committee and involved in Gravity Theory Trust proposal for financial support.
Albert Einstein Institute, Germany
21-28 Apr 2021
Current challenges in gravitational physics WORKSHOP
Part of organizing committee.
SISSA (online), Italy

Commitments in the organization of regular group meetings and journal clubs

WS22 - now
Waveform systematics working group
Organizing the activities of the internal working group on waveform systematics.
Albert Einstein Institute, Germany
WS20-WS21
IFPU Journal Club
Bi-weekly journal club connecting the host institutes in the area of Trieste.
IFPU, Italy
SS20-WS20
ERC GRAMS Group Meetings
Weekly group meetings/journal club of the ERC GRAMS group.
SISSA, Italy
WS17/18-SS19
TAT Group Meetings
Weekly group meetings/journal club of the theoretical astrophysics group.
University of Tübingen, Germany

Contact

Email
sebastian.voelkel@aei.mpg.de
Address
Sebastian Völkel
Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
Am Mühlenberg 1
14476 Potsdam
Germany

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