This is how a star can be turned into a planet!
Yes! A star can turn into a planet, however, this change just occurs for an extremely specific kind of star known as a brown dwarf. A few researchers don't believe brown dwarfs to be genuine stars since they lack enough mass to light the atomic combination of normal hydrogen. Simultaneously, a few researchers don't believe Brown dwarfs to be genuine planets because of the fact that they regularly sit at the center of a star system group, just like a star.
But what the heck is a Brown dwarf?
A brown dwarf is a bizarre thing with a mass that is more prominent than the greatest customary planets (i.e. above 13 times the mass of Jupiter) and not exactly the littlest ordinary stars (i.e. below 80 times the mass of Jupiter). Although a brown dwarf does not have enough inward gravitational pressure to ignite the nuclear fusion of regular hydrogen, it does have enough to ignite the nuclear fusion of heavy hydrogen (deuterium).
Early in the life of a brown dwarf, the nuclear fusion of its heavy hydrogen releases large amounts of light and heat. As a result, a young brown dwarf glows just like a regular star.
What about its name? Are they really brown?
Despite its name, a brown dwarf that is still glowing does not appear brown at all! Rather, it appears magenta or reddish-orange as they emit light on their own, just usually not very much.
From a distance, brown dwarfs look very similar to their cousins, Red dwarfs. Despite beginning life as a star, a brown dwarf quickly uses up its heavy hydrogen, goes dark, cools, and spends the rest of its life like a planet.
Wait! What is heavy hydrogen or deuterium?
An atom of deuterium is very much like an atom of ordinary hydrogen except that it has a neutron in its nucleus in addition to its proton. This additional thing in its nucleus makes it heavier. This neutron likewise acts as an extra atomic paste, making it easier to fuse two atoms of heavy hydrogen! Furthermore, deuterium is uncommon in the universe and in stars than normal hydrogen. Therefore, a brown dwarf cannot burn its regular hydrogen and quickly burns up its heavy hydrogen (because there is a scarcity of it).
So, what is it the Ultimate fate of a brown dwarf?
A brown dwarf stops emitting light and heat, early in its lifetime. Then it cools down and dims until it behaves more like a huge planet like Jupiter. A brown dwarf sits in the center of a star system as a regular star, but it spends the rest of its life looking and acting like an ordinary planet. In such a star system, the end result is a collection of planets orbiting a large central planet with no star to be found anywhere! Such systems eventually become cold, dark, and lonely places. They are simply failed stars.
*Note: Some brown dwarfs orbit regular stars*
Are brown dwarfs real or is it some hypothetical stuff?
Starting in 2018, more than 3000 brown dwarfs have been discovered. This doesn't imply that brown dwarfs are very rare. It simply implies that brown dwarfs are very difficult to detect. An analysis estimates that there are about as many brown dwarfs in our galaxy as there are ordinary stars! So, they are not rare at all!