In a discovery decades in the making, scientists have detected the first of a 'theoretical' class of stars first proposed in 1975 by physicist Kip Thorne and astronomer Anna Zytkow. Thorne-Zytkow objects are hybrids of red supergiant and neutron stars that superficially resemble normal red supergiants, such as Betelguese in the constellation Orion. They differ, however, in their distinct chemical signatures that result from unique activity in their stellar interiors.

Source: Astronomers discover first Thorne-Zytkow object, a bizarre type of hybrid star