Theoretically, it is possible for a type of celestial object called a quark star to exist, which is composed of quark matter instead of the usual nuclear matter found in stars. Quark matter is a hypothetical form of matter consisting of quarks that are not confined within hadrons (such as protons and neutrons) but exist in a deconfined state.
Quark stars are postulated to form under extreme conditions of temperature and density, such as those present in the core of a massive neutron star. As the density increases, it is believed that nuclear matter undergoes a phase transition, and the quarks within it become deconfined and form a dense state of quark matter.
The precise properties and behavior of quark matter under such extreme conditions are still the subject of ongoing research and theoretical investigation. It is not yet fully understood how quark matter behaves and whether stable, self-sustaining quark stars can exist.
However, it is important to note that quark stars, if they exist, would be highly exotic and different from conventional stars that primarily undergo nuclear fusion of hydrogen into helium. The energy generation mechanism in quark stars would involve the interactions and transformations of quarks themselves, rather than nuclear fusion processes.
At present, no confirmed observations of quark stars have been made, and their existence remains a topic of scientific exploration and theoretical speculation.