Gesa H.-M. Bertrang


Gesa H.-M. Bertrang

I use the powerful tool of polarization to characterize dust grains and magnetic fields!

Getting to know the looks of dust grains at the various stages of planet formation, and, at the same time, constraining disk evolution by probing for magnetic fields, that's the unique power of polarization. However, to achieve this, it is necessary to keep simulations and observations working closely together. That is what I am pursuing, currently as Postdoctoral Researcher at Max Planck Institute for Astronomy, Heidelberg, Germany.
In my free time, after I've enjoyed the vast beauty of Chile, I am now exploring Germany's far South  (↳photos).
On the following pages, I prepared an overview for you about myself and my research. Enjoy!


Aiming at understanding the formation of planets and low-mass stars, with a focus on dust characterisation and the role of magnetic fields, I use both, 3D radiative transfer simulations as well as observations. My work is carried out in the optical, near-infrared (e.g., VLT/SPHERE), and (sub-)millimeter wavelength ranges (ALMA).


Research is done best when done open-mindedly.
This applies to our on-hand work and even more so to the community itself. Promoting equal opportunities for everyone is essential to me. I pursue this as Conflict Coach, LGBT* Rights Advocate, and previously as Postdoc Representative


I grew up in Kiel, in North Germany, where I later studied and earned my doctorate. I was a post-doctoral fellow at U de Chile and U Diego Portales in Santiago de Chile before I awarded a position as Postdoctoral Researcher at Max Planck Institute for Astronomy. Since summer 2018, I work on Königstuhl in Heidelberg, Germany.

Upcoming talks:

2021 May - GRAVITY cons. meeting, virtual space

2021 Jun - EAS 2021, Leiden, virtual space

full CV

New Papers


Radiative Scale Height and Shadows in Protoplanetary Disks

2021 ApJ 910, 31

Gap, shadows, spirals, and streamers: SPHERE observations of binary-disk interaction in GG TAuri A

2020 A&A 639, 62

Self-scattering on non-spherical dust grains

2020 A&A 638, 116

Disks Around T Tauri Stars with SPHERE (DARTTS-S) II: Twenty-one new polarimetric images of young stellar disks
2020 A&A 633, 82

Invited Talks


2020 Nov - #FasziAstroOnline, HdA, Youtube

2020 Aug - Herzberg Astrophysics DRAO, Virtual Space

2020 May - Workshop: Protoplanetary Disk Chemodynamics, Potsdam

2020 Apr - Workshop: Building Blocks of Planets, Ringberg Castle

2020 Jan - Astrophysical Colloquium, Tübingen

2019 Nov - Science of Early Life conference,  Kloster Seeon

2019 Oct - ESO,  Garching

2019 Aug - Disks2Planets workshop, Ringberg Castle

2019 Aug - NOAO, Tucson

2019 Aug - MIT, Kavli Institute

2019 Aug - Harvard, CfA

2019 Aug - Boston University, Dep. of Astronomy

2019 Mar - Oxford, AOPP




My academic career


march 2011 -
september 2015
Kiel University
PhD student
Advisor: Sebastian Wolf

PhD (Dr. rer. nat.) on "Observations and simulations of polarized radiation as tracer of magnetic fields in star formation"...

october 2005 -
november 2010
Kiel University
Student (Dipl.-Phys.)
Advisor: Sebastian Wolf

Diploma in physics (Dipl.-Phys.) Thesis title: "Magnetic fields in star formation"...

Work experience

since June 2018
Max Planck Institute for Astronomy
Senior postdoctoral research associate
Advisor: Mario Flock

Senior postdoctoral research associate in the UFOS group ( at Max Planck Institute for Astronomy....

march 2017 -
march 2018
Universidad de Chile
Advisor: Laura Perez

Grant (~125,000 USD) from the Chilean government to carry out independent research, hosted at Universidad de Chile (w Laura Perez)....

october 2015 -
march 2017
U de Chile & U Diego Portales
MAD Fellow
Advisors: Simon Casassus & Lucas Cieza

Grant (~112,000 USD) to carry out independent research within the Millenium ALMA Disk nucleus (MAD), hosted at Universidad de Chile (w Simon Casassus) and Universidad Diego Portales (w Lucas Cieza)....


full CV


What I do

Young stars are surrounded by disks of dust and gas. These circumstellar disks are the birthplaces of planets. Understanding the physical processes in these disk is vital for the understanding of planet formation. It has been predicted that magnetic fields are an important factor on a wide range of physical processes in protoplanetary disks, such as the migration of planet(esimals) and the mere evolution of disks. Yet, observational constraints are still pending. In the classical picture, (sub-)mm continuum polarisation is the tracer for magnetic fields in disks. Aspherical dust grains, whose thermal emission is intrinsically polarized, get aligned by the magnetic field due to radiative torques. In recent years, however, this picture has been challenged. New theoretical studies show that (sub-)mm continuum polarisation can also be created by scattering of the thermal dust emission or arise from aspherical grains which are aligned by the radiation field rather than the magnetic field. These three mechanisms trace fundamentally different physics in protoplanetary disks, yet, their polarisation predictions are not clearly distinguishable. I am applying 3D radiative transfer simulations of the polarized continuum and gas emission in combination with observations to disentangle the different mechanisms behind the measured polarization aiming at constraining magnetic fields in protoplanetary disks.

Publications: Bertrang 2015 (PhD thesis); Bertrang+2017; Bertrang & Wolf 2017; Flock+2017

ALMA showed us that protoplanetary disks are not only highly structured but also so abundant in dust that their (sub-)mm emission often appears to be optically thick. This opens a new way to probe for grain sizes by observing self-scattering. However, the grain size inferred from self-scattering are challenging the understanding of grain growth - the newly derived values are simply too small. This contradiction between theoretical expectations along with indirectly measured grain sizes and those derived from self-scattering originates, so my hypothesis, from the oversimplification of the dust model (a perfect sphere) in current self-scattering models. This forces us to realize: a novel, more realistic dust model is essential to move on.

Publications: Kirchschlager, Bertrang, Flock 2019; Kirchschlager & Bertrang (2020, accepted)

As planets form and grow in dusty, gaseous circumstellar disks, mutual gravitational interactions between disk and planet lead to a series of phenomena such as gaps, warps, or spiral arms. I make use of multi-wavelength observations performed with VLT/SPHERE and ALMA  in combinations with radiative transfer simulations to  test for signals of this interaction.

Publications: Bertrang+2018; Xu+2015; Cieza+2017; Avenhaus+2018; Cieza+2019

The role of magnetic fields in the process of star formation is a matter of continuous debate. Clear observational proof of the general influence of magnetic fields on the early phase of cloud collapse is still pending. Multi-wavelength polarimetry (optical - mm), tracing magnetic fields on scales of 10^3-10^6au in Bok globules, reveal a strong polarization signal and strongly aligned polarization vectors on large scales (Bertrang+2014, Jorquera & Bertrang 2018). This indicates dominant magnetic fields across Bok globules with simple as well as complex density structures. To reconcile our findings in globules, the lowest mass clouds known, and the results on intermediate (e.g., Taurus) and more massive (e.g., Orion) clouds, we postulate a mass dependent role of magnetic fields, whereby magnetic fields appear to be dominant on low and high mass but rather sub-dominant on intermediate mass clouds.

Publications: Bertrang+2014; Bertrang 2015 (PHD thesis); Jorquera & Bertrang 2018

Mentoring: I am co-supervisor of two PhD students, Lizxandra Flores and Marcelo Barraza (MPIA). At U de Chile, I supervised the Bachelor student Sebastian Jorquera, together we published our work on magnetic fields in Bok globules (Jorquera & Bertrang 2018).

Teaching: I am experienced as teaching assistant of several courses on undergrad level at Kiel University (Physics IV: nuclear physics, particle physics, astrophysics and cosmology; Elementary mathematical methods in physics I & II).

  I enjoy talking science not only with scientist but just as much with the public. Upcoming and past outreach events are:

- 2020 Nov: Talk at "#FasziAstroOnline" at HdA, Heidelberg/YouTube
- 2020 Jan: Talk at "Faszination Astronomie" at HdA, Heidelberg
- 2019 Nov: Talk at the Koblenz Technology Night, Koblenz
- 2019 Jul:  Talk to the 50th anniversary of MPIA at HdA, Heidelberg
- 2019 Jan: Talk at Astronomy on Tap, "Making the invisible visible", Heidelberg
- 2015 Jun: Newspaper article to the 350th anniversary of Kiel University
- 2013 Jun: Girls Day, Solar observations, Kiel University


Get in touch with me

Get in touch

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My address

skype: gesa.bertrang
phone: +49 6221 528 367

Max Planck Institute for Astronomy
Room 318
Königstuhl 17
69117 Heidelberg, Germany