Mimas, moon of Saturn
Shock Wave Awe
As stars move through the interstellar medium, their magnetic fields and the solar wind of particles flowing off the star collide with the gas and dust around them. These interactions can set up a bow shock, energizing and illuminating the diffuse medium in front of the star. Our own Sun, an average sized and relatively slow moving star, produces a bow shock, although it is nearly invisible at all wavelengths of light.
But things change when the star in question is big and fast moving. Take, for example, the runaway star Kappa Cassiopeiae (Kappa Cas), also known as HD 2905. It lies some 3,500 light years away in the constellation Cassiopeia, and is visible to the naked eye. This supergiant is 40 times more massive, is about 4 times hotter, shines some 420,000 times brighter, and has a radius 40 times that of our Sun. HD 2905 is a big, hot, bright star that pumps massive amounts of energy into its surroundings. Oh, and it is moving through those surroundings at a high rate of speed, some 1,100 kilometers/684 miles per second relative to its neighbors.
The combined impact of that solar energy and velocity set up a huge shock wave in front of this star. Seen here in an infrared image from the Spitzer Space Telescope, the bow shock is shown in red, highlighting the 24 micron wavelength. The shock wave is an amazing 4 light-years ahead of Kappa Cassiopeiae. For comparison, that’s about the same distance that we are from Proxima Centauri, the nearest star to our own Sun. That’s what I call star power!
Image credit: NASA/JPL-Caltech
Sources: 1, 2
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