Classical Cepheid variables are a special class of stars that exhibit period variation in their observed brightness. These are typically young population III stars with high masses, usually 3 – 30 solar masses.

There are three primary techniques for studying binary star systems. The first technique, direct imaging, allows astronomers to visually resolve both stars in the binary system when they are sufficiently separated.

Theories about the first black holes suggest they formed shortly after the Big Bang, either as "heavy seeds" born from the direct collapse of massive gas clouds or as smaller "light seeds" from the remnants of early stars