MATINS (magneto-thermal evolutIon of isolated neutron stars in 3D): public release

[Clara Dehman]

Dear all,

Over the past decades, significant effort has been devoted to understanding the evolution of isolated neutron stars during their lifetimes, which presents challenges from both physical and numerical perspectives. The temperature and magnetic field of neutron stars evolve together in a complex way. Extremely strong magnetic fields influence how heat flows through the star’s solid crust, channeling thermal energy along preferred directions and insulating some regions
while exposing others. At the same time, these magnetic fields are not static: they can change their geometry due to the Hall drift, and as they gradually decay, they release energy that can partially reheat the star. Understanding this coupled magnetothermal evolution is therefore essential to correctly interpret neutron-star observations, and especially their apparent diversity.

Several magneto-thermal codes in the past had to choose to either employ detailed microphysics in simplified (axially symmetric) geometries or addressing fully three-dimensional configurations at the expense of using more approximate physical assumptions. In the past
few years, we tried to overcome this by developing MATINS (MAgneto-Thermal evolutIon of Isolated NSs), funded by the European Research Council (ERC 'MAGNESIA' No. 817661): a three-dimensional numerical framework designed to model the magnetothermal evolution of the crust of isolated neutron stars. MATINS computes the neutron star structure by solving the Tolman–Oppenheimer–Volkoff equations for a range of nuclear matter equations of state, enabling systematic studies across different stellar masses. The code solves the induction equation in the crust, including both Ohmic dissipation and Hall drift, tod escribe magnetic-field evolution. This is coupled to a fully 3D thermal cooling model based on state-of-the-art microphysical inputs: conductivities, heat capacities, neutrino processes, with the options
of different superfluid and superconductive gap models. To solve the governing equations in three-dimensional spherical geometry, MATINS employs a finite-volume scheme on a cubed-sphere grid. Each radial shell is covered by six smoothly connected patches, analogous to
inflating a cube into a sphere, thereby avoiding the coordinate singularities at the axis of standard spherical coordinates. This new framework stems directly from the 2D magneto-thermal code developed in the past 20 years at the University of Alicante, adapted to a 3D grid
and with additional features including parallelization with openMP. The code can be used to model a variety of observable properties of isolated neutron stars, including X-ray thermal emission, surface magnetic fields, temperature maps, and rotational evolution (spin period and its derivative).

We are happy to announce the public release of the MATINS code that can be now accessed at: https://ice-csic-astroexotic.github.io/code/matins .

Details on how to install and run the code are also available at the above website, together with the reference articles explaining more technical details. For any queries you can write at:
mat...@ice.csis.es. Apologies if you receive this message more than once.

Best wishes,

Stefano Ascenzi
Clara Dehman
Davide De Grandis
José A. Pons
Nanda Rea
Daniele Viganò