51 Pegasi

51 Pegasi is a Sun-like star located approximately 50 light-years away in the constellation Pegasus. It is significant for being the first Sun-like star discovered to host an extrasolar planet, 51 Pegasi b, which was detected in 1995 by Michel Mayor and Didier Queloz. This discovery revolutionized the field of exoplanet research and challenged existing theories of planetary formation.

The star is a G-type main-sequence star, similar to our Sun but slightly older and more massive. It has a spectral type of G5V. Its apparent magnitude is around 5.5, making it faintly visible to the naked eye under ideal conditions.

51 Pegasi b, the exoplanet orbiting 51 Pegasi, is a gas giant roughly half the mass of Jupiter. It orbits incredibly close to its star, with an orbital period of just over four days. This proximity makes it a "hot Jupiter," a class of exoplanets characterized by high temperatures and short orbital periods. The discovery of 51 Pegasi b was pivotal because it demonstrated that giant planets could exist in very close orbits around their host stars, contradicting previously held assumptions about planetary system architectures.

The name "51 Pegasi" follows the Flamsteed designation system, where stars are numbered within constellations in order of right ascension.