The conventional wisdom is that if sentient life exists elsewhere in the universe, it probably lives on another planet. But in 2020, the physicists Luis Anchordoqui and Eugene Chudnovsky argued that we should consider the possibility that life (including technologically advanced civilizations) might exist inside stars.
Their argument relies upon a very expansive view of the definition of life. They admit that biological life couldn't exist inside a star, but they argue that high-energy physics supplies various "nuclear objects" such as "strings, monopoles, and semipoles" that might be able to encode information and form a self-replicating system (i.e. life).
Their hypothesis is, of course, highly speculative, but they suggest it might provide an explanation for a previously unexplained phenomenon observed in some stars:
Cosmologists have observed stars at all stages of development and decline and can calculate a star’s life cycle based on features like size, heat, and light. As stars age, for instance, they begin to cool and radiate less light. Occasionally, however, a younger star is observed to dim for unknown reasons, as if it is cooling more rapidly than expected.
“There are no theories that explain it,” Chudnovsky said. “So maybe it’s a very complicated process related to the function of a civilization inside the star.”
If a star harbored a nuclear civilization within it, he explained, the energy used to sustain that civilization would cause the star to cool and dim faster—in effect speeding up the aging process. And, at some point, the star would no longer produce enough energy to sustain this form of life.
More info: Lehman College News Center
; "Can Self-Replicating Species Flourish in the Interior of a Star"