What happens to the outer layers of a red giant during its transformation into a planetary nebula?

During the transformation of a red giant into a planetary nebula, the outer layers of the star are expelled into space. This process occurs as the star undergoes significant changes in its internal structure and temperature. As a red giant evolves, it sheds its outer material, which creates a glowing shell of gas and dust around the central core.

The ejected layers contribute to the interstellar medium, enriching it with heavy elements that were formed during the star's lifecycle. This ejection of material is not a violent explosion like a supernova; instead, it is a gentle release of the outer layers of the star as it transitions into the planetary nebula stage. The central remnant left behind will eventually cool and shrink, becoming a white dwarf.

In contrast, the other responses do not accurately describe this process. The outer layers do not remain intact within the star or get absorbed by the core; instead, they separate and disperse. Additionally, the layers being ejected as a supernova misrepresents the nature of a planetary nebula, as a supernova is a different phenomenon that typically involves massive stars rather than the lower-mass stars that become planetary nebulae.