B Simulating the Universe's First Stars - The Population III Stars

[jedishrfu]

https://dailygalaxy.com/2025/08/universe-first-stars-reveal-cosmic-chaos/

A groundbreaking set of supercomputer simulations is offering a vivid glimpse into how the universe’s first stars, known as Population III stars, emerged from the chaos of the early cosmos.

These simulations, led by Ke-Jung Chen of the Institute of Astronomy and Astrophysics at Academia Sinica in Taiwan and detailed in a study published in The Astrophysical Journal Letters, reveal that violent turbulence in primordial gas clouds played a far more significant role in star formation than previously thought.

They used the Gizmo multi-physics simulation engine:

Welcome!

GIZMO is a flexible, massively-parallel, multi-physics simulation code. The code lets you solve the fluid equations using a variety of different methods -- whatever is best for the problem at hand. It introduces new Lagrangian Godunov-type methods that allow you to solve the fluid equations with a moving particle distribution that is automatically adaptive in resolution and avoids the advection errors, angular momentum conservation errors, and excessive diffusion problems that limit the applicability of “adaptive mesh” (AMR) codes, while simultaneously avoiding the low-order errors inherent to simpler methods like smoothed-particle hydrodynamics (SPH). Meanwhile, self-gravity is solved fast, with fully-adaptive gravitational softenings. And the code is massively parallel — it has been run on everything from a Mac laptop to >1 million CPUs on national supercomputers.

I started a separate thread on Gizmo in the Computers and Technology forum:

Thread 'Gizmo -- a multi-physics simulation engine'

Aug 10, 2025

Found this Gizmo engine in an article on simulating Population III stars in the early universe.

http://www.tapir.caltech.edu/~phopkins/Site/GIZMO.html

Welcome!

GIZMO is a flexible, massively-parallel, multi-physics simulation code. The code lets you solve the fluid equations using a variety of different methods -- whatever is best for the problem at hand. It introduces new Lagrangian Godunov-type methods that allow you to solve the fluid equations with a moving particle distribution that is automatically adaptive in resolution and avoids the advection errors, angular momentum...

• jedishrfu
• Replies: 1
• Forum: Computing and Technology

• 

 

[fresh_42]

I would be interested in how those turbulences overcome the thermal pressure caused by the still very hot gases. I thought that temperature was the main reason why star formation in the early universe was difficult to impossible.

Here is the paper:
https://iopscience.iop.org/article/10.3847/2041-8213/adf18d/pdf

They talk about it in section 3.2 and 3.3., but I don't understand the details. Maybe someone can explain it in simple words.

Unlike subsonic or transonic flows, supersonic turbulence can compress and shock the gas, leading to the formation of clumpy structures such as giant molecular clouds in the Milky Way.

How?

 

[jedishrfu]

They talk about the turbulence being supersonic and out-muscling the thermal pressure and making denser regions that can coalesce.

 

[sbrothy]

I've always found it counterintuitive that the first ones are population 3, then 2, then 1. But I'm sure there's a perfectly simple explanation I could dig up myself.

 

[BWV]

Curious on the rationale / significance of the gas being supersonic and why are they measuring speed relative to sound?

Also if the effects of dark matter on current individual stars / solar systems is negligible, only impacting things at a galactic level, what was different about it back then?

 

[Ibix]

Curious on the rationale / significance of the gas being supersonic and why are they measuring speed relative to sound?

The speed of sound in a medium is basically the maximum speed at which the material can dissipate energy into its bulk. That's why a supersonic aircraft can make a shock wave that can break your windows from miles away.

Supersonic turbulence is new to me, but I would suspect that the point is that subsonic turbulence would allow collisions between gas molecules to carry away energy, so overpressure regions can to some extent dissipate by spreading out, while supersonic turbulence has changes that are too fast for such dissipative mechanisms to work. That would mean that you can get much higher overpressure and much steeper pressure changes, which sounds very like conditions that could promote star formation.

It might be worth asking someone who knows something about fluid dynamics to comment. Perhaps someone like @Chestermiller knows something about supersonic turbulence.

Also if the effects of dark matter on current individual stars / solar systems is negligible, only impacting things at a galactic level, what was different about it back then?

The point about dark matter is that it doesn't clump, so in modern times it has a similar galactic scale average density to normal matter but remains diffuse. That makes it more or less irrelevant to solar systems that are well modelled as a few point masses, but very relevant to galaxies that can be modelled as a fluid. But here we're talking about the beginning of clumping, and normal matter is diffuse too at the beginning of the process so even on sub-galactic scales its interactions with dark matter could be important.