The formation of stars requires gas. In star clusters, because a large amount of gas will be dissipated in the early stage of star cluster formation, star clusters have been considered to be unable to form new stars. Only collisions or mergers between stars are likely to be old. Stars replenish burning matter. They look younger than the rest of the stars. Stars formed by collisions or mergers are called blue discrete stars, and their name comes from their very different evolutionary processes compared to most stars. This keeps them out of the evolutionary trajectory of theoretical predictions. A research team used observational data to study the blue discrete stars in the young star cluster NGC.2173, and for the first time observed an unusual group of blue discrete stars in this young cluster. According to the discovery, this star cluster contains blue discrete stars formed by sudden bursts. The text is intended to explain:. ['Star formation requires gas.', 'Unusual blue discrete stars in star clusters.', 'Blue Discrete Stars Escape from the Evolutionary Track of Theoretical Prediction.', 'Stars formed by collision or merger are called blue discrete stars.']