Chandra takes a fresh look at giant Runaway star Zeta Ophiuchi

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 that companion was destroyed in a supernova explosion; Spitzer’s infrared data reveals a dramatic shock wave (red and green) that was formed by material flying off the star’s surface and turning into gas on its way; Chandra data (blue) shows an X-ray emission bubble located around the star, produced by gas that was 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 about 440 light years away in the constellation of Ophiuchus.

Also called 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 would appear blue to the eye.

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

It is believed that when the companion exploded in a supernova, taking most of its mass away, Zeta Ophiuchi was suddenly released from its partner’s pull and was shot like a bullet traveling at 100,000 km/h (161,000 km/h). mph).

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

New data from NASA’s Chandra X-ray Observatory shows an X-ray emission bubble located around the star, produced by gas that has been heated by the effects of the shock wave to tens millions of degrees.

In a new study, Dr Samuel Green of the Institute for Advanced Study, Dublin and colleagues have carried out the first detailed computational investigation of the arc shock of Zeta Ophiuchi to test whether a simple model of the arc shock can explain the observed nebula, and to compare the 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.

The three different models predict weaker X-ray emission than observed.

The X-ray emission bubble is brightest near the star, while two of the three models predict that the X-ray emission should be brightest 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 bubbling energetics and wind-dissipative processes of a massive star can be studied, and as such it is an ideal laboratory for constraining 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 important questions, but our work can be used as a basis for building more complicated models including the inhomogeneous interstellar medium and turbulent, anisotropic heat conduction, particle acceleration and transport, and more detailed wind models.

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

Their article 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 the press; doi: 10.1051/0004-6361/202243531

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