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Nico Schuster, Cosmologist

Tools & Visualizations

Three projects live here:

The two visualizations are fully interactable directly on this page. For a larger view on their own dedicated pages, use the Open in full window option below the embeds. Both were built using the SAIL framework (Scientist-AI-Loop). You can read more about this workflow on my publications page or directly in the paper.

Cosmic Web Explorer
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Experience the formation of the universe’s large-scale structure right in your browser via this real-time, interactive simulation. Built as a pedagogical “2.5D” model, it combines second-order Lagrangian perturbation theory (2LPT) with a local, quasi-N-body gravity scheme, rendered via WebGL and WebGPU for high performance, to let you watch primordial fluctuations collapse into voids, filaments, and halos from redshift z=10 to the present day.

While the physics are simplified compared to realistic N-body simulations to maintain interactive performance, the Cosmic Web Explorer includes a robust suite of genuine analysis features:

  • Real-time void identification: Uses a custom-coded Voronoi-watershed algorithm in the spirit of VIDE/ZOBOV.
  • Dynamic measurements: Live calculations of void density profiles, normalized density distributions, power spectra or correlation functions, redshift-space distortions, and more.
  • Adjustable cosmologies: Switch seamlessly between \( \Lambda \)CDM, \(w \)CDM, and \(w_0 w_a \)CDM models and change their parameter values to see how the cosmic web responds.

Moreover, the tool also lets you export videos and snapshots, and you can even write your own text into the cosmic web (see the banner at the top of this page for an example). While the tool by default uses realistic initial conditions, it also has an additional “BAO Init.” mode, which places amplified rings from Baryon Acoustic Oscillations on top of the initial density field to highlight this cosmological feature in the resulting structures.

Cosmic Web Explorer Open in full window ↗

Source code: github.com/nicosmo/cosmic_web_explorer

Credits: Initial concept by Simon Bouchard and Nico Schuster; developed by Nico Schuster; code generation assisted by Google Gemini and Claude. Thanks to Julien Zoubian and Dennis Frei for their contributions to the code, and to many colleagues for useful discussions and feedback.

How to cite: Schuster, N., Bouchard, S., Zoubian, J., & Frei, D. (2026). Cosmic Web Explorer (v1.1.0). Zenodo, doi:10.5281/zenodo.18915566. AGPLv3.

Gravitational Lensing Visualization
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An interactive WebGL visualization of gravitational lensing that lets you bend and distort the light of background galaxies in real time. By dragging a massive foreground cluster or void across your screen, you can instantly see how gravitational fields warp the space around them and explore how changing the parameters of the lens affects the distortions.

The tool is built for intuition, utilizing inverse ray-tracing in a fragment shader under a thin-lens approximation, as well as amplified distortions to illustrate the core physical effects. To further isolate these effects, you can toggle between different backgrounds, such as a grid to visualize spacetime distortions, dots to observe magnification and shear, or even your own uploaded image. It allows you to actively switch between several models of mass distributions:

  • Multiple cluster models: Test a simple point mass, an NFW dark-matter halo, or an elliptical lens with visible critical curves and caustics to explore effects of strong and weak lensing.

  • Realistic void profiles: Visualize how underdensities act as diverging lenses, using both a simplified toy model and the realistic HSW profile.

  • Real-time rendering: The fragment-shader implementation ensures smooth, immediate feedback as you reposition the lens and change its parameters.

Gravitational Lensing Visualization Open in full window ↗

Source code: github.com/nicosmo/lensing_visualization

Credits: Concept and visualization by Nico Schuster and Andrés Salcedo; code generation assisted by Google Gemini. Thanks to Dennis Frei for his contributions to the code, and to many colleagues for useful discussions and feedback. The caustic and critical-curve algorithms build on the lenstronomy package.

How to cite: Schuster, N., Salcedo, A. N., & Frei, D. (2026). Visualizing Gravitational Lensing (v1.0.0). Zenodo, doi:10.5281/zenodo.18914869. CC0.

Void Profile Analysis Toolkit
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A Python toolkit for measuring, saving, and stacking radial profiles around cosmic voids in cosmological simulations. The code computes the density and velocity profiles of tracers in spherical shells around void centers, stacks multiple voids to achieve high signal-to-noise measurements, and estimates uncertainties using Jackknife resampling. Built for efficiency, it processes profiles in parallel and natively integrates with the VIDE library when available (falling back to SciPy otherwise while maintaining periodic boundary conditions). This toolkit serves as the core analysis pipeline behind several of my publications.

Source code: github.com/nicosmo/void_profile_analysis

How to cite: Schuster, N. (2025). Void Profile Analysis Toolkit (Software). Zenodo, doi:10.5281/zenodo.17967174.

This code implements methods from arXiv:2210.02457, arXiv:2312.11241, and arXiv:2509.07092, so check out their methods sections for more details.