1) In Norse mythology, the Valkyries are divine maidens who serve Odin, the chief god. They are responsible for selecting warriors worthy of entering Valhalla and escorting them to the afterlife. They are often depicted as powerful and beautiful figures, riding winged horses and wielding spears.

2) The first photograph of a black hole was captured in 2019 using a network of telescopes around the world.

3) The concept of sovereignty refers to the supreme authority and power of a state to govern itself, make decisions, and control its own territory without interference from external forces.

4) The Pacific Ocean is the largest ocean on Earth, covering more than 30% of the planet's surface.