Matteo Cantiello | Stellar Physics

The Life and Death of Stars


The night sky is the silent backdrop of human experience.

It is populated by an incredibly large number of stars, separated by vast distances and mostly empty space. We now know that there is a profound connection between these objects and our own existence: Not only stars lighten up an otherwise dark Universe, but through their lifecycle also produce and shed the fundamental elements required by biological life. All the elements we are made of, except for hydrogen, have been forged inside the hot and dense cores of stars. The calcium in our bones, the iron in our blood, the nitrogen and oxygen in the air and in our DNA. Basically every important ingredient of life came from the stars. We are literally made of stardust.

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Massive Stars

Studying stars humans discovered that, aside from hydrogen, all of  the elements we are made of have been synthesized inside stars. A star is a self-regulating system, with the amount of energy released by nuclear burning is exactly the amount needed to counteract the gravitational force.

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Binary Stars

If the equilibrium is perturbed, the star readjust its structure, such that the nuclear reactions provide again the right amount of energy.  In this way stars can be stable for long timescales during hydrogen burning (the so-called main sequence). This phase cannot last forever, since the amount of fuel inside of stars is finite, and energy is released only from the fusion of isotopes lighter than iron.

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Magnetic Fields

When a sufficient amount of energy can no longer be extracted from the rest mass of the star, the  battle against gravity is lost. Then the final fate of the star depends on the mass of the object: low mass stars end their lives as white dwarfs, while massive stars (more massive than about 8 solar masses) die in spectacular explosions or disappear quietly forming a black hole.

Computational Tools

Since 3D stellar evolution is not feasible in the foreseeable future, progress in our understanding of the physics and evolution of stars relies on the synergy between local 3D (radiation) MHD calculations and 1D stellar evolution modeling.

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DEDALUS

DEDALUS is a flexible framework for solving differential equations using spectral methods. It is open source, written in Python and MPI-parallelized. Key features are symbolic equation entry, spectral domain discretization and implicit-explicit timestepping.

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ATHENA++

Athena++ is a complete re-write of the Athena astrophysical magnetohydrodynamics (MHD) code in C++. Features include flexible coordinate and grid options including adaptive mesh refinement (AMR), radiation transport and general relativity, significantly improved performance and scalability, and improved source code clarity and modularity.

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MESA

MESA, Modules for Experiment in Stellar Astrophysics, is an open source software instrument widely adopted in the astrophysics community. The star module allows to calculate the 1D stellar structure and evolution of single and binary stars. The full capabilities of MESA are documented in the instrument papers. I have been a member of the MESA council since 2013.