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Radial Velocity Method-Detecting Exoplanets
In the previous article, we explained exoplanets, their types, and briefly discussed the methods astronomers use to find these planets. In this article, I will explain the Radial Velocity method in detail.
The radial velocity method or RV method is the most effective method for detecting the presence of an exoplanet or an exoplanetary system. Astronomers don’t directly observe a planet through this method, but they do this indirectly. We know from Newton’s law of Gravitation, if two bodies are close enough they will attract each other.
So, if a planet is orbiting a star, it will exert a gravitational force on the star and pull the star towards it. But the star, if it’s very massive, won’t feel much pull. But if the planet is massive enough, it will make the star wobble. Astronomers then use the light from the star to see if it is wobbling or not. So, wobbling stars are the best candidates for finding exoplanets.
51 Pegasi b is the first exoplanet to be discovered using this method in 1995.
Astronomers use the doppler effect to see if a star is wobbling or not. This phenomenon was first discovered by Christian Doppler, one and a half centuries ago. According to Doppler, when a source of the wave is moving away or towards us, the frequency of the wave will vary.
If the wave is moving towards us, its frequency will increase and if the wave is moving away from us the frequency of the wave will decrease, like in the figure below. When the source of sound is moving towards us, the sound frequency increases and vice versa. This idea of him revolutionized our understanding of the universe.
In his own words,
It is almost to be accepted with certainty that this theory will — in the not too distant future — offer astronomers a welcome means to determine the movements and distances of such stars.
