A fast-moving star collides with interstellar gas, creating a spectacular arc shock
Zeta Ophiuchi’s multi-wavelength view. Credits: X-Rays: NASA/CXC/Dublin Inst. Advanced Studies/S. Green et al.; Infrared: NASA/JPL/Spitzer
Zeta Ophiuchi has an interesting life. It started out as a typical massive star about twenty times as massive as the sun. It spent its days happily orbiting a large companion star until its companion exploded as a supernova about a million years ago. The explosion took out Zeta Ophiuchi, so now he was speeding through interstellar space. Of course, supernovae also eject the outer layers of companion stars, so instead of empty space, our intrepid star is also traveling through the rest of the gas. As they say on Facebook, it’s complicated. And that’s great news for astronomers, as a recent study shows.
Zeta Ophiuchi is most famous for the beautiful pictures above. By plowing through interstellar gas, the star has created heat shockwaves that shine in everything from infrared to X-rays. The physics of these shock waves are very complex. It is governed by a set of mathematical equations known as magnetohydrodynamics, which describe the behavior of a fluid gas and the surrounding magnetic field. The modeling of this equation is pretty bad, but when you have turbulent motion like a shock wave, things get even worse. That’s why Zeta Ophiuchi is so important. Since we have a very good view of the shockwave, we can compare our observations with computer simulations.
In this new study, the team created a computer model that simulates shock waves near Zeta Ophiuchi. They then compared this model with observations in infrared, visible, and X-rays. The goal is to determine which simulation is the most accurate so that the model can be further refined. 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 observed. But all three models also predict that X-ray emission should be fainter than what we observe, so neither model is completely accurate. But this model is difficult to do well, and this work is a good start.
Zeta Ophiuchi simulation shockwave. Credit: Green, et al
The difference in the brightness of the X-rays is likely due to the turbulent motion in the shock wave. The team plans to include some of these turbulent movements in future models. Through several iterations, they should be able to create simulations that model these interstellar shock waves.
Magnetohydrodynamics is a central part of many astrophysical processes, from solar flares to planet formation, to the engine of powerful quasar black holes. Most of these interactions are hidden by distance or dust, so it’s great that Zeta Ophiuchi can give astronomers a surprising look at this complex physics.
Blow up power lines underwater to understand the shock wave
S. Green et al, Thermal emissions from arc shock. II. Ophiuchi zeta 3D magnetohydrodynamic model, Astronomy & Astrophysics (2022). DOI: 10.1051/0004-6361/202243531
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