Quasi-stars are theoretical celestial bodies. Unlike a regular star, which has a core where the process of nuclear fusion goes on, a Quasi Star has a Black Hole at its centre. Astronomers say that if such a Star existed, it would dwarf even the biggest of stars in the known universe- estimates show that Quasi-stars may be billions of kilometers wide!
Quasi Stars are theorized to have come from extremely large Protostars (young stars). Scientists believe that extremely large Protostars could had existed in the very early stages of the universe because of the high abundance of hydrogen and helium. But, what does a Protostar have to do with a black hole and a Quasi-star? A very Large star would have a very massive core. Due to the enormous amount of mass above the core, the core would be highly compressed and go supernova. Due to the extreme mass and density of the core, the supernova would result in a black hole.
Even though the process of fusion ends, the Star does not die. The energy of the supernova is absorbed by the outer layers of the star due to their size and mass. This is how we end up with a black hole inside a star. From the outside, a Quasi-Star would look like a normal star, but at its core, a black hole is eating it from the inside out. It will take the Black Hole an estimated few million years to completely devour the star.
How Quasi-stars may forward our understanding of the Universe?
The Quasi-star idea could be key to understanding many things in the universe today. For example, this type of star can provide an explanation for today’s supermassive black holes. Nobody knows how Supermassive Black Holes got as big as they are today (some of them are even larger than the solar system!). But if Quasi-stars really existed in the early universe, they would had provided young Black holes with huge amounts of material to consume and allow them to grow to the size they are today.