Hi!

I am a PhD candidate at the Max Planck Institute for Astronomy in Heidelberg and interested in observational astronomy, binary stars and black holes.

In September 2023, I started my PhD at MPIA Heidelberg, where I am working with Professor Hans-Walter Rix on the search for dormant black holes. Based on high-resolution, multi-epoch spectroscopy, I search for and characterize binary star systems with possible compact companions. I am interested in uncovering the formation pathways of these systems and, more broadly, in constraining the properties of the black hole population in the Milky Way.

Before that, I did my undergraduate studies at the University of Göttingen and have spent two semesters abroad at the Universities of Padova and Stockholm. In my Master's thesis, I studied spectroscopic binaries in globular clusters, working with Professors Stefan Dreizler and Sebastian Kamann and the MUSE consortium.

Key Interests

  • Binary star systems
  • (Integral field) Spectroscopy
  • Black holes and compact objects
  • Spectral Disentangling
  • Globular clusters
  • Bayesian Statistics

Image Credit: 47 Tuc by NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration Acknowledgment: J. Mack (STScI) and G. Piotto (University of Padova, Italy)

Research

Hunting for dormant black holes in the Milky Way

While population synthesis models anticipate billions of stellar-mass BHs in the Milky Way, only a few have been identified, mostly in X-ray-emitting, accreting binary systems. My research instead concentrates on dormant BHs in detached binary systems. These BHs induce distinct variations in their companion's radial velocity, flux, and light-centroid position, offering an indirect detection method.
Image Credit: ESO/Calçada, L.

Binary properties of the globular cluster 47 Tuc (NGC 104)

Observations of binary stars in globular clusters are essential to understand cluster dynamics, shed light on the formation of peculiar stellar objects and to probe the elusive populations of dark stellar remnants. Using multi-epoch data from the VLT/MUSE integral field spectrograph, I have analysed the binary population of 47 Tuc, one of the oldest and most massive Galactic globular clusters. Results include the identification of several hundred binary candidates based on radial velocity variability, a new estimate of the total binary fraction in the cluster and constraints on the number of black holes in binary systems in 47 Tuc.
Image Credit: ESA/NASA/Hubble

Gap-opening planets around type-A stars

During a summer internship @MPIA Heidelberg, I worked on theoretical planet formation models under the supervision of Dr. Gabriele Pichierri and Dr. Bertram Bitsch. I investigated whether and under what circumstances the presumed gap-opening planets in protoplanetary disks around young stars could represent progenitors of the discovered exoplanet population. More specifically, I simulated the evolution of the embedded planets during the lifetime of the disk and analysed the dependence of the final planetary masses and orbital parameters on the disk viscosity.
Image Credit: DSHARP survey, Andrews, S. et al.

Cosmological parameter inference from the distribution of dark matter halos

In 2021, I worked on a cosmological project at the Oskar Klein Centre in Stockholm with Dr. Jens Jasche as part of an ERASMUS internship. My work there focused on inferring cosmological parameters from the large scale density distribution of galaxies using convolutional neural networks (CNN). For the project, I worked with a subset of Quijote N-body simulations from which I generated training data. The CNN achieved significant improvement in prediction accuracy compared to related work, especially regarding Omega matter.

Publications

You can find my publications on ADS or the arxiv.

First-author papers

  • Müller-Horn, J. et al. "Emerging population of gap-opening planets around type-A stars. Long-term evolution of the forming planets around HD 163296", A&A, Volume 663, A163, 2022: ADS, arxiv.

    • Co-author papers

  • Saracino, S. [and 9 others including Müller-Horn, J.] "A closer look at the binary content of NGC 1850", MNRAS, Volume 526, 2023: ADS, arxiv.

    • Presentations

  • Two in a million - The interplay between binaries and star clusters @ ESO, Garching (09/2023)
    "Binary Properties of the Globular Cluster 47 Tuc (NGC 104)"
    Contributed talk, slides available via Zenodo

  • The Renaissance of Stellar Black-Hole Detections in The Local Group @ Lorentz Center, Leiden (06/2023)
    "The Binary Population of NGC 104 - Searching for Stellar Remnants in Globular Clusters with MUSE" Poster presentation

    • Contact

    • mueller-horn@mpia.de
    • Room 114-A
      Max-Planck-Institut für Astronmie
      Königstuhl 17
      D-69117 Heidelberg, Germany