A new study suggests that black holes may not be the featureless, structureless entities that Einstein’s general theory of relativity predicts them to be. Instead, the cosmic monsters might be bizarre quantum objects known as “frozen stars.”

“Frozen stars are a type of black hole mimickers: ultracompact, astrophysical objects that are free of singularities, lack a horizon, but yet can mimic all of the observable properties of black holes,” Ramy Brustein, a professor of physics at Ben-Gurion University in Israel, told Live Science in an email. “If they actually exist, they would indicate the need to modify in a significant and fundamental way Einstein’s theory of general relativity.”

Brustein is a co-author of a study describing the frozen star theory, published in July in the journal Physical Review D.