How do hot blue-white stars compare to cooler stars in terms of absorption lines?

Hot blue-white stars exhibit fewer absorption lines compared to cooler stars because the high energy of these stars leads to a different ionization state of their outer layers. In hotter stars, the temperatures are sufficient to ionize hydrogen and other elements more completely. As a result, there are fewer neutral atoms available to absorb specific wavelengths of light, which leads to fewer visible absorption lines in their spectra.

In cooler stars, where temperatures are lower, more atoms remain in a neutral state, allowing them to absorb light at specific wavelengths and thus create numerous absorption lines. This contrast in the spectra provides crucial insights into the composition and temperature of the stars. Consequently, hot blue-white stars have a characteristic spectra that reflects their high temperatures and unique chemical environments, resulting in fewer absorption lines overall.