How does the 'wobble' of a star due to an orbiting planet cause detectable spectral changes?
Answer
As the star wobbles toward us, we see a minute blueshift; as it wobbles away, a redshift.
The Radial Velocity Method, heavily utilized in exoplanet hunting, relies on detecting the minute gravitational influence a planet exerts on its host star. As the planet orbits, the star 'wobbles' slightly around their common center of mass. When the star wobbles toward the observer, its light exhibits a tiny blueshift; subsequently, as it wobbles away, it exhibits a redshift. Although this periodic motion-induced shift is much smaller than the star's overall galactic orbital motion, the regular, repeating pattern of these minuscule shifts betrays the presence of an orbiting companion.
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