HV 2210 is a star which is located 1,99,000 light years from us in the Small Magellanic cloud (a satellite galaxy of our milky way) in Tucana constellation.
It looks like a red gaint from outside but when light emitted from it was studied it was found rich in elements like Molybdenum, lithium, Strontium, Yttrium and Rubidium. A normal super gaint also contain these elements but not in such high amount.
Thats why it was proposed that it is a Throne-Zytkow object.
Thorne-Zytkow object is a type of star which is formed by the collision of a red giant or supergiant star with a neutron star. When a star goes into supernova and leads to the formation of a neutron star, a passing by red supergiant star collides with the neutron star and absorbs it forming a hybrid star. So in other words its a star inside a star!!!
From outside its a red supergiant whereas the core is formed by a neutron star
It is still being studied to be confirmed as a Hybrid Star.