About Me

Ciao, my name is Sebastian Völkel and I am a postdocotoral researcher in the ERC group of Enrico Barausse at SISSA and IFPU, which are located in Trieste, Italy. Before moving here in 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 in the following.

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.

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]. Currently I am extending the inverse spectrum methods to address more complex systems and work on gravitational wave parameter estimation using Bayesian analysis [10]. I have also been working on using the shadow-size of the supermassive black hole M87*, as observed by the Event Horizon Telescope Collaboration, to test strong-field general relativity [11]. My latest work is on using Bayesian inference to relate neutron star oscillations with their parameters [13], which we also reviewed along with related techniques [14].

Latest News

2021

18 Nov
Gave a talk for the Theoretical Astrophysics group at the University of Tübingen, Germany.
11 Nov
Gave a talk at the 31st Midwest Relativity Meeting, University of Illinois in Urbana-Champaign, USA (remotely).
13 Oct
Released a blog article about our recent work on black hole shadows.
11 Oct
Class. Quantum Grav. published our recent letter on EHT tests of the strong-field regime of General Relativity.
04 Oct
We submitted our new work on Separating Astrophysics and Geometry in Black Hole Images.
28 Sep
Front. Astron. Space Sci. published our review on Fast Rotating Neutron Stars: Oscillations and Instabilities.
30 Aug
Gave an invited talk at the Dissertation Prize Symposium of the German Physical Society (DPG) Section Matter and Cosmos meeting, Jena, Germany (remotely).
22 Jul
Gave a talk at Amaldi14, Australia (remotely).
17 Jul
Received the Promotionspreis of the University of Tübingen, Germany.
07 Jul
Gave a talk at the Mathematical Physics Colloquium at the University of Tübingen, Germany (remotely).
21 Apr
Our workshop on Current Challenges in Gravitational Physics has started (21.-28. April 2021, remotely).
09 Apr
Phys. Rev. D published our paper on "Bayesian inverse problem of rotating neutron stars".
01 Apr
Gave a talk at the Meeting of the National Research Group on Gravitational Waves, Paris (remotely).
18 Feb
Gave a talk at the INFN TEONGRAV Workshop 2021 (remotely).
15 Feb
Phys. Rev. D published our paper on "An exact theory for the Rezzolla-Zhidenko metric and self-consistent calculation of quasi-normal modes".
01 Feb
Presenting a poster at the 740. WE-Heraeus-Seminar: Experimental Tests and Signatures of Modified and Quantum Gravity, 01.-05. February 2021, Bad Honnef, Germany (remotely).
29 Jan
We are organizing a workshop on Current Challenges in Gravitational Physics, 21.-28. April 2021 (remotely).

2020

21 Dec
Gave a talk at the XIII Black Holes Workshop, Lisbon, Portugal (remotely).
16 Nov
Submitted our recent work on EHT tests of the strong-field regime of General Relativity.
19 Oct
Gave an invited talk at the Sapienza University of Rome, Italy (remotely).
12 Oct
Phys. Rev. D published our paper on "Bayesian Metric Reconstruction with Gravitational Wave Observations".
30 Sep
Gave an invited talk at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Germany (remotely).
28 Sep
Gave an invited talk at the Institut d'Astrophysique de Paris (IAP), France (remotely).
09 Jul
Gave an invited talk for the Theoretical Astrophysics group at the University of Tübingen, Germany (remotely).
07 Jul
Gave an invited talk at the AstroCoffee meeting at the Goethe University Frankfurt, Germany (remotely).
03 Jun
My PhD thesis has been published.
08 May
Finally defended my PhD thesis at the Univeristy of Tübingen, Germany!
30 Apr
Gave an invited talk in the Gravity seminar at the University of Southampton, Southampton, UK (remotely).
13-16 Jan
Attended Gravitational Waves, Black Holes and Fundamental Physics in Trieste, Italy.
08 Jan
Gave an invited talk at the University of Stuttgart, Stuttgart, Germany.

Curriculum Vitae

Academic Track Record

Postdoc
2019-now, 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 Journal Articles

[14]
Separating Astrophysics and Geometry in Black Hole Images
Guillermo Lara, Sebastian H. Völkel, and Enrico Barausse
accepted for publication in Phys. Rev. D., 2021
Link to arxiv
[13]
Bayesian inverse problem of rotating neutron stars
Sebastian H. Völkel, Christian 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
accepted for publication, in press
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.1]
Fast Rotating Neutron Stars: Oscillations and Instabilities
Christian 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

Others

[O.3]
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
[O.2]
The Sound of Exotic Astrophysical "Instruments"
Sebastian H. Völkel and Kostas D. Kokkotas
CQG+, May 28, 2018
Link to the blog
[O.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.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 and Schools

[T.16]
Constraining black holes with quasi-normal modes
Presenting 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
Presenting 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
Presenting 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
Presenting my work at the INFN TEONGRAV Workshop 2021
18. Feb 2021, Italy (remotely)
[T.12]
Metric reconstruction with gravitational waves and shadows
Presenting my work at the XIII Black Holes Workshop
21. Dec 2020, Lisbon, Portugal (remotely)
[T.11]
Master Class of Brian P. Schmidt
Presenting my field at the "69th Lindau Nobel Laureate Meeting"
03. July 2019, Lindau, Germany
[T.10]
Hearing the Nature of Compact Objects
Presenting 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
Presenting my research at NEB18
21 September 2018, Rhodes, Greece
[T.6]
Hearing the Nature of Compact Objects
Presenting 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 Talks

[OT.2]
Gravitationswellen und kompakte Objekte: Einsteins kosmisches Orchester
Invited talk at the Arbeitskreis Astronomie
08 January 2020, University of Stuttgart, Germany
[OT.1]
The Sound of Black Holes
My contribution to the Science Slam at the Doctoral Candidates’ Convention
21 February 2018, University of Tübingen, Germany

Posters

[P.4]
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.3]
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
[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

Commitments in the organization of regular group meetings and journal clubs

WS20-now
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@sissa.it
Address
Sebastian Völkel
SISSA Scuola Internazionale Superiore di Studi Avanzati
Via Bonomea 265
34136 Trieste TS, Italy