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Computer simulations are providing new insights into the rampage of man-eating neutron stars.
When a neutron star swallows material from a close binary companion star, the unstable thermonuclear combustion of the accumulated material can create a violent explosion of X-rays throughout the universe.
Exactly how these powerful eruptions evolve and spread across the surface of a neutron star is something of a mystery. But by trying to recreate the observed X-ray flares using simulations, scientists are learning more about their interiors and exteriors, as well as the ultra-dense neutron stars that produce them. Masu.
“Simulations allow us to see these phenomena in much more detail,” said Michael Zingale, a computational astrophysicist at the State University of New York at Stony Brook.
“One of the things we want to do is understand the properties of neutron stars, because we want to understand how matter behaves at the extreme densities we see in neutron stars.”
Neutron stars are some of the densest objects in the universe. These are what’s left after a giant star completes its life, runs out of fuel, and explodes into a supernova.
But while the outer material was flung into space, the star’s core collapsed under gravity, forming an ultra-dense sphere about 20 kilometers (12 miles) in diameter, a tiny sphere containing up to 2.3 suns. It packs about a minute’s worth of mass.
You’d expect matter packed this densely to be a bit bizarre, to say the least. But scientists can study thermonuclear explosions and place constraints on their size, which could help model their interiors.
For various reasons (distance, danger, etc.) we cannot get up close and observe neutron stars in detail, but we can gather as much information as we can about their X-rays. Let’s put together a simulation that generates a burst and whose results match the observed data.
Although it sounds simple, the physics of neutron stars is extremely complex. Simulating their behavior requires a lot of computing power.
In a previous study, researchers used Oak Ridge National Laboratory’s Summit supercomputer to simulate a thermonuclear flame in two dimensions. Now, they have built on that work and scaled up the simulation to his third dimension.
“The big goal is always to connect simulations of these events with what we observe,” Zingale explains. “We aim to understand what the underlying stars are like, and it is essential to explore what these models can do across dimensions.”
The model’s 3D neutron star was millions of times hotter than the Sun and rotated at 1,000 revolutions per second, which is quite close to the theoretical upper limit for how fast neutron stars can spin. They then simulated the early evolution of a thermonuclear flame.
Although the flame in the 2D simulation spread slightly faster than the 3D version, the growth trends for both models were very similar. This agreement means that 2D simulations remain a great tool for studying these hectic explosions, but there are still some things they can’t do.
For example, turbulence behaves differently in two and three dimensions. However, you can use 2D shims for things that can be done with 2D shims, freeing up computing power for other things, such as increasing write fidelity.
Armed with this information, we can run simulations to gain real insight into how neutron stars throw their incredible tantrums.
“We’re getting closer to modeling a flame that spreads across the star from pole to pole,” Zingale says. “I’m looking forward to it.”
This study astrophysical journal.
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