Which of the following describes an explosion in space caused by a star?

A supernova is an astronomical event that occurs during the last evolutionary stages of a massive star, marked by a dramatic explosion. This event happens when a star exhausts its nuclear fuel, causing a sudden collapse of its core under gravity. This implosion generates immense pressure and temperature, ultimately leading to a powerful explosion that ejects the outer layers of the star into space.

Supernovae are critically significant for various reasons. They not only play a crucial role in enriching the interstellar medium with heavy elements, but they also can trigger the formation of new stars from the material they expel. The light produced from a supernova can briefly outshine entire galaxies, making these events visible across vast distances.

Other choices, such as a solar flare, refer to a different phenomenon involving the Sun's activity, which does not result in an explosion of this magnitude. White dwarfs and red giants are stages in stellar evolution but do not represent explosive events. Therefore, the defining characteristic of a supernova as an explosion resulting from a star's life cycle makes it the correct choice for this question.