What type of electromagnetic wave helps astronomers to determine the hottest stars?

Astronomers use ultraviolet (UV) electromagnetic waves to determine the hottest stars. These stars emit significant amounts of their energy in the ultraviolet spectrum due to their high temperatures, often exceeding 30,000 Kelvin. By analyzing the UV light they emit, astronomers can gauge their surface temperatures and understand their physical properties. This information is crucial for studying stellar evolution and the characteristics of different types of stars.