Zeta Ophiuchus is a very massive, hot, bright blue star that once had a companion that exploded as a supernova.
Zeta Ophiuchi was once in close orbit with another star before being ejected when that satellite was destroyed in a supernova explosion; infrared data from Spitzer reveal a spectacular shock wave (red and green) that is formed by matter blown off the star’s surface and slamming into gas on its way; the Chandra data (blue) show a bubble of X-ray emission surrounding the star produced by gas that has been heated by the shock wave to tens of millions of degrees. Image credit: NASA / CXC / University of Cambridge / Sisk-Reynés et al. / NSF / NRAO / VLA / PanSTARRS.
Zeta Ophiuchus is located approximately 440 light-years away in the constellation Ophiuchus.
Also known as HD 149757, HR 6175 or IRAS 16343-1028, this star is about 20 times more massive and 65,000 times brighter than the Sun.
If it weren’t surrounded by so much dust, it would be one of the brightest stars in the sky and would appear blue to the eye.
Zeta Ophiuchi was probably once part of a binary system with an even more massive companion.
When the satellite exploded as a supernova, blowing off most of its mass, Zeta Ophiuchi is thought to have suddenly broken free of its partner’s gravitational pull and shot out like a bullet traveling at 161,000 km per hour (100,000 mph) .
Previously released infrared data from NASA’s Spitzer Space Telescope revealed a spectacular shock wave that formed from matter blown off the star’s surface and slamming into gas on its way.
New data from NASA’s Chandra X-ray Observatory show a bubble of X-ray emission surrounding the star produced by gas that has been heated by the effects of the shock wave to tens of millions of degrees.
In a new study, Dr. Samuel Green of the Dublin Institute for Advanced Study and colleagues performed the first detailed computational study of the Zeta Ophiuchi shock to test whether a simple bow shock model could explain the observed nebula and compare detected X-ray emission with simulated emission maps.
They tested whether computer models could explain data obtained at different wavelengths, including X-ray, optical, infrared and radio observations.
All three different models predict weaker X-ray emission than observed.
The X-ray bubble is brightest near the star, while two of the three models predict that the X-rays should be brighter near the shock wave.
In the future, the authors plan to test more complex models with additional physics – including the effects of turbulence and particle acceleration – to see if the agreement with the X-ray data will improve.
“The shocked wind region around Zeta Ophiuchi is the closest object to Earth where the bubble energetics and dissipative processes for the wind of a massive star can be studied, and as such is an ideal laboratory to constrain the relevant physical processes,” they said.
“This first numerical study of the bow shock and wind bubble around Zeta Ophiuchi does not provide simple answers to the important questions, but our work can be used as a basis for building more complex models, including inhomogeneous and turbulent interstellar medium, anisotropic thermal conductivity, particle acceleration and transport and more detailed wind models.
“Better observational data would also be very helpful, as the existing X-ray data set has significant diffuse emission contamination from stellar radiation.”
Their paper will be published in the journal Astronomy & Astrophysics.
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S. Green et al. 2022. Heat emission from bow strokes. II. 3D magnetohydrodynamic models of Zeta Ophiuchus. A&A, in press; doi: 10.1051/0004-6361/202243531
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