Skylight.jl

General-relativistic ray tracing and radiative transfer in arbitrary spacetimes

Documentation is under construction, and is available here.

Skylight works with any spacetime geometry, without the constraints of specific symmetries or the assumption of asymptotic flatness. It is designed with the following goals in mind:

• Fast computational speed
• High accuracy
• Easy extensibility to user-defined spacetimes and radiative models

It uses automatic differentiation with ForwardDiff.jl to compute the Christoffel symbols from the spacetime metric, and has built-in multithreading parallelism. The integration of the equations is performed with DifferentialEquations.jl.

For a quick start guide, see Getting started.

Features

Supported spacetimes

• Minkowski spacetime
• Schwarzschild spacetime
• Kerr spacetime
• Johannsen spacetime
• f(R)-Kerr spacetime
• Ruffini-Argüelles-Rueda spacetime for fermionic dark matter
• Boson star spacetimes with quartic self-interaction and solitonic potentials
• Extensibility to user-defined spacetimes

Radiative models

• Shakura-Sunyaev accretion disk
• Novikov-Thorne accretion disk
• Ion tori with synchrotron and bremsstrahlung emission
• Geometrically-thin optically-thick accretion disks with user-provided tabulated temperatures
• Line emission from accretion disks with user-provided emissivity profiles
• Lamppost corona emission and accretion disk illumination profiles
• Circular hot spots on the surface of a neutron star
• Extensibility to user-defined radiative models

Geometric and dynamical tools

• Spacetime metrics, inverse metrics, volume elements, Christoffel symbols, etc.
• Four-vector scalar products, index raising/lowering, orthogonal projection, normalization, etc.
• Constants of motion in spacetimes with symmetries
• Characteristic radii, like event horizons, ISCOs, etc.
• Spacetime geodesics integration

Radiative transfer

• Radiative transfer in vacuum and in emissive/absorptive media

Observable quantities

• Bolometric and specific intensities
• Fluxes through arbitrarily oriented surface elements
• Images and spectra
• Generic observation frames (any position and four-velocity)

Utilities

• Loading/saving data and configurations from/to HDF5 files
• Units and dimensions management

Installation

Requirements

• Julia version at least 1.6

The package is not yet available in the Julia registries. To install it, follow these steps:

1. Clone the repository: git clone https://github.com/joaquinpelle/Skylight.jl.git
2. Open the Julia REPL and enter package mode by typing ].
3. Add Skylight to your Pkg environment: dev \path\to\the\repository
4. Exit package mode with Ctrl + C and import Skylight: using Skylight

Folder contents

.
├── docs                    # Documentation files
├── run                     # Example scripts and notebooks to run the code
├── src                     # Source files
├── test                    # Test files 
│   ├── benchmarks          # Load and stress tests
│   ├── integration         # End-to-end, integration tests
│   └── unit                # Unit tests

To run the unit tests

1. In your terminal, go to the package directory
2. Open the Julia REPL
3. Go to the package mode by typing ]
4. Activate the package environment by running the command activate .
5. In the package mode, run the command test

To cite this work

If you use this software in your work, we kindly request that you cite the following paper

@article{pelle2022skylight,
  title={Skylight: a new code for general-relativistic ray-tracing and radiative transfer in arbitrary space--times},
  author={Pelle, Joaquin and Reula, Oscar and Carrasco, Federico and Bederian, Carlos},
  journal={Monthly Notices of the Royal Astronomical Society},
  volume={515},
  number={1},
  pages={1316--1327},
  year={2022},
  publisher={Oxford University Press}
}