Zeta Ophiuchi was once in close orbit with another star, before being ejected when this companion was destroyed in a supernova explosion; infrared data from Spitzer reveal a spectacular shock wave (red and green) that was formed by matter blowing away from the star’s surface and slamming into gas in its path; data from Chandra (blue) show a bubble of X-ray emission located around 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.

Chandra Takes New Look at Giant Runaway Star Zeta Ophiuchi | Sci-News.com

Zeta Ophiuchi 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 this companion was destroyed in a supernova explosion; infrared data from Spitzer reveal a spectacular shock wave (red and green) that was formed by matter blowing away from the star’s surface and slamming into gas in its path; data from Chandra (blue) show a bubble of X-ray emission located around 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 Ophiuchi is located approximately 440 light-years away in the constellation of Ophiuchus.

Also known as HD 149757, HR 6175 or IRAS 16343-1028, this star is about 20 times more massive and 65,000 times more luminous than the Sun.

If it weren’t surrounded by so much dust, it would be one of the brightest stars in the sky and appear blue to the eye.

Zeta Ophiuchi was likely once part of a binary system with an even more massive companion.

It’s believed that when the companion exploded as a supernova, blasting away most of its mass, Zeta Ophiuchi was suddenly freed from its partner’s pull and shot away like a bullet moving 161,000 km per hour (100,000 mph).

Previously released infrared data from NASA’s Spitzer Space Telescope revealed a spectacular shock wave that was formed by matter blowing away from the star’s surface and slamming into gas in its path.

The new data from NASA’s Chandra X-ray Observatory show a bubble of X-ray emission located around 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 from the Dublin Institute for Advanced Studies and his colleagues made the first detailed computational investigation of Zeta Ophiuchi’s bow shock to test whether a simple model of the bow shock can explain the observed nebula, and to compare the detected X-ray emission with simulated emission maps.

They tested whether the computer models can explain the data obtained at different wavelengths, including X-ray, optical, infrared and radio observations.

All three of the different models predict fainter X-ray emission than observed.

The bubble of X-ray emission is brightest near the star, whereas two of the three models predict the X-ray emission should be brighter near the shock wave.

In the future, the authors plan to test more complicated models with additional physics — including the effects of turbulence, and particle acceleration — to see whether the agreement with X-ray data will improve.

“The shocked-wind region around Zeta Ophiuchi is the closest object to Earth where bubble energetics and dissipative processes for the wind of a massive star can be investigated, and as such it is an ideal laboratory for constraining the relevant physical processes,” they said.

“This first numerical study of the bow shock and wind bubble around Zeta Ophiuchi does not give simple answers to the important questions, but our work can be used as a basis for building more complicated models including inhomogeneous and turbulent interstellar medium, anisotropic thermal conduction, particle acceleration and transport, and more detailed wind models.”

“Better observational data would also be very helpful because the existing X-ray dataset has significant contamination of the diffuse emission by stellar emission.”

Their paper will be published in the journal Astronomy & Astrophysics.

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S. Green et al. 2022. Thermal emission from bow shocks. II. 3D magnetohydrodynamic models of zeta Ophiuchi. A&A, in press; doi: 10.1051/0004-6361/202243531

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