Giant Star Zeta Ophiuchi and Bow Shock

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This infrared image from NASA's Spitzer Space Telescope shows the giant star Zeta Ophiuchi and the bow shock, or shock wave, in front of it. Visible only in infrared light, the bow shock is created by winds that flow from the star, making ripples in the surrounding dust. Located roughly 370 light-years from Earth, Zeta Ophiuchi dwarfs our Sun: It is about six times hotter, eight times wider, 20 times more massive and about 80,000 times as bright. Even at its great distance, it would be one of the brightest stars in the sky were it not largely obscured by dust clouds.

This massive star is travelling at a snappy pace of about 24 kilometers per second, fast enough to break the sound barrier in the surrounding interstellar material. Because of this motion, it creates a spectacular bow shock ahead of its direction of travel (to the left). The structure is analogous to the ripples that precede the bow of a ship as it moves through the water, or the sonic boom of an airplane hitting supersonic speeds. The fine filaments of dust surrounding the star glow primarily at shorter infrared wavelengths, rendered here in green. The area of the shock pops out dramatically at longer infrared wavelengths, creating the red highlights. A bright bow shock like this would normally be seen in visible light as well, but because it is hidden behind a curtain of dust, only the longer infrared wavelengths of light seen by Spitzer can reach us.

Bow shocks are commonly seen when two different regions of gas and dust slam into one another. Zeta Ophiuchi, like other massive stars, generates a strong wind of hot gas particles flowing out from its surface. This expanding wind collides with the tenuous clouds of interstellar gas and dust about half a light-year away from the star, which is almost 800 times the distance from the sun to Pluto. The speed of the winds added to the star's supersonic motion result in the spectacular collision seen here.

Image Credit: NASA/JPL-Caltech

Image enhancement: Jean-Baptiste Faure