Can a star cool down enough and become a giant planet?
user
Yes, a star can turn into a planet, but this transformation only happens for a very particular type of star known as a brown dwarf. Some scientists do not consider brown dwarfs to be true stars because they do not have enough mass to ignite the nuclear fusion of ordinary hydrogen.
assistant
How is a brown dwarf formed? What makes it different from other dwarf stars?
user
Brown dwarf stars form in a similar way to other stars, through the collapse of a molecular cloud. However, unlike other stars, brown dwarfs do not have enough mass to ignite hydrogen fusion in their cores, which is what makes a star shine.

Other dwarf stars, on the other hand, are stars that have a mass roughly between that of a brown dwarf and the Sun, and do sustain hydrogen fusion.
assistant