Chapter 1: Introduction to Exoplanets

In the preceding article, we delved into exoplanets, their various classifications, and the techniques astronomers employ to discover them. This piece will focus specifically on the Radial Velocity method.

Understanding the Radial Velocity Method (Image Credit: NASA)

The Radial Velocity method, often abbreviated as RV method, stands as one of the most proficient techniques for identifying exoplanets or their systems. Instead of directly observing the planets, astronomers utilize indirect methods. According to Newton’s law of Gravitation, two nearby bodies exert gravitational attraction on one another. Therefore, when a planet orbits a star, it influences the star's position through gravitational pull. While a massive star may not show significant movement, a sufficiently large planet can induce a noticeable wobble in the star's motion. By analyzing the star's light, astronomers can detect this wobbling, making such stars prime targets for exoplanet discovery.

51 Pegasi b marked the inaugural detection of an exoplanet via this method back in 1995.

Astronomers leverage the Doppler effect to assess whether a star exhibits this wobble. Discovered by Christian Doppler over a century ago, this phenomenon states that the frequency of a wave changes as its source moves towards or away from an observer. When a wave approaches us, its frequency appears higher, while it seems lower when receding. This principle has significantly enhanced our comprehension of the cosmos.

The Doppler Effect Explained

In Doppler's 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."

Importantly, the Doppler effect is not confined to sound; it applies to all wave types. For light, if it moves toward us, it is blue-shifted, while light moving away becomes red-shifted, correlating to their respective frequencies.

When a star approaches us, the wavelengths of its emitted light decrease (indicated in the graph), while wavelengths increase and shift toward red when the star moves away (Image Credit: ESA). If the star shows periodic red and blue shifts, it suggests wobbling, which is the basis of the RV method. This technique is also known as Doppler spectroscopy. Although efficient, it requires the planet to possess sufficient mass; otherwise, it may not yield results.

The first video titled "Detecting Exoplanets: Radial Velocity Method" provides a comprehensive overview of how this technique operates and its significance in astronomy.

Chapter 2: Further Insights into Exoplanets

Exoplanets, or extrasolar planets, are those that orbit stars outside our solar system. Their study is crucial in understanding the diversity of planetary systems.