A fast-moving star collides with interstellar gas

Zeta Ophiuchi has had an interesting life. It started out as a typical large star, about twenty times more massive than the sun. It spent its days orbiting a large companion star until it exploded as a supernova about a million years ago. The explosion ejected Zeta Ophiuchi, who is now speeding away into interstellar space. Of course, the supernova also expelled the outer layers of its companion star, so instead of empty space, our brave star is racing through the residual gas. As they say on Facebook, it’s complicated. And that’s great news for astronomers, as a recent study shows.

Zeta Ophiuchi is best known for her gorgeous images, like the one above. As it passes through the interstellar gas, the star has created heated shock waves that shine in all fields, from infrared to X-rays. The physics of these shock waves is very complex. The physics of these shock waves is extremely complex. It is governed by a set of mathematical equations known as magnetohydrodynamics, which describes the behavior of fluid gases and the magnetic fields around them. Modeling these equations is hard enough, but when it comes to turbulent motions such as shock waves, things get even more complicated. This is why Zeta Ophiuchi is so important. Since we have such a great view of his shock wave,

In this latest study, the team created computer models simulating the shock wave near Zeta Ophiuchi. They then compared these models to infrared, visible and X-ray observations. Their goal is to determine which simulations are the most accurate so that they can refine the models. Of their three models, two of them predicted that the brightest region of X-ray emission should be at the edge of the shock wave closest to the star, and this is what we observe . But all three models also predicted that X-ray emissions should be lower than what we observe, so none of the models is completely accurate. But these models are difficult to make correctly, and this work is a good start.

A simulated shockwave from Zeta Ophiuchi. Credit: Green, et al

The difference in X-ray brightness is likely due to turbulent motion within the shock wave. The team plans to include some of this turbulent motion in future models. Through multiple iterations, they should be able to create a simulation that closely models this interstellar shock wave.

Magnetohydrodynamics is central to many astrophysical processes, from solar flares to planet formation to the powerful black hole engines of quasars. Most of these interactions are hidden by distance or dust. That’s why it’s great that Zeta Ophiuchi can give astronomers a shocking insight into this complex physics.

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