How did Michel Mayor and Didier Queloz detect 51 Pegasi b?

In 1995, Swiss astronomers Michel Mayor and Didier Queloz detected 51 Pegasi b using the radial velocity method.12

Beginning in 1994, the pair observed 142 stars at the Haute-Provence Observatory in France using a new spectrograph called ELODIE. This instrument allowed them to measure a star's radial velocity—its motion toward or away from the observer—with high precision. When a planet orbits a star, both bodies orbit a common center of mass, causing the star to "wobble". This motion induces a shift in the star's spectral lines, which can be detected as a Doppler effect.314

While observing the star 51 Pegasi, Mayor and Queloz identified a periodic wobble in a 4.23-day cycle. This signature revealed the presence of a planet with about half the mass of Jupiter orbiting very close to its parent star. Their discovery of this "hot Jupiter" was the first confirmed detection of an extrasolar planet orbiting a sunlike star, for which they were awarded the 2019 Nobel Prize for Physics.153