More recently, 5,800 gamma-ray sources (such as stars) were examined by the Fermi Gamma-ray Space Telescope. Out of the 5,800, it found 14 which gave off gamma-rays with energies that could be expected from antimatter-matter annihilation!
It’s an improbable and crazy thought that antistars could exist. The current theory is that while antimatter and matter were both present in the early universe, something caused matter to ‘win over’ antimatter, leaving no antimatter apart from that produced in occasional collisions. One hypothesis for this lies in the behavioural differences of neutrinos compared to anti-neutrinos.
Other theories however allow for small clumps of antimatter to be left behind, which would fit in with the idea of antistars. These clumps of antimatter would have to assemble in areas of low-density of normal matter so as not to be annihilated, which could make them more common in our galactic halo (outermost parts of our galaxy) and globular clusters. It can be hard to tell whether such stars are made of antimatter or matter; they would act in the same way, giving off the same light and heat that others do.
Of course, given the highly speculative nature of theories surrounding antistars, it is important to note that this research and its hypotheses are in their elementary phase. Still, the implications of this are exciting for developing our understanding of the early universe.