Stars May Make Bow Shock Waves

When objects move through a medium, they often push the medium out of their way, creating a wave like the bow wave of a boat pushing water away. When an aircraft is pushing air away in a bow wave, as the speed of the craft nears the speed of sound, the wave becomes compressed into what is known as a bow shock wave. The bow shock wave of a super-sonic aircraft is responsible for the sonic boom.

Interstellar space is not empty, being occupied mostly by highly dispersed gases and also some dust and cosmic radiation. When a star moves through the gas in “empty” space, it creates a bow wave from the pressure of the solar “wind” plasma pushing against the gases. If the difference between the solar wind and the gas in space around it is not great, a “gentle” bow wave is created. But if the difference is large, a bow shock wave can be created. That shock wave gives off infrared radiation that can be detected even when the star may not be easily visible. Looking for the infrared signature of a bow shock wave is one way to locate distant stars that are moving at extreme velocity.

UW Researchers Discover Runaway Stars Leave Infrared Waves in Space – [uwyo.edu]

In the last year, astronomers from the University of Wyoming have discovered roughly 100 of the fastest-moving stars in the Milky Way galaxy with the aid of images from NASA’s Spitzer Space Telescope and Wide-field Infrared Survey Explorer (WISE), and use of the Wyoming Infrared Observatory (WIRO) on Jelm Mountain near Laramie.

When some swift, massive stars — moving at speeds faster than 50,000 miles an hour — plow through space, they can cause material to stack up in front of them in the same way that water piles up ahead of a ship or a supersonic plane creates a shockwave in front of it. Called bow shocks, these dramatic arc-shaped features in space are helping researchers to uncover massive, so-called runaway stars.

Zeta Ophiuchi — Runaway Star Plowing Through Space Dust – [nasa.gov]

The blue star near the center of this image is Zeta Ophiuchi. When seen in visible light it appears as a relatively dim red star surrounded by other dim stars and no dust. However, in this infrared image taken with NASA’s Wide-field Infrared Survey Explorer, or WISE, a completely different view emerges. Zeta Ophiuchi is actually a very massive, hot, bright blue star plowing its way through a large cloud of interstellar dust and gas.

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