prompter: Can a star cool down enough and become a giant planet?

assistant: There is a continuum of sorts between very small stars (Red Dwarves) and very large planets (Gas Giants). In between these two, there are the Brown Dwarves, also known as "failed stars".
Different parts of the fusion chain, starting with hydrogen and eventually ending with iron, take different amounts of energy to produce.
Brown dwarves are not able to complete the entire fusion chain, and eventually fizzle out.
The precise classification of these objects can vary between sources, but arguably these are the sorts of objects you describe in your question.

assistant: No, a star cannot cool down enough to become a giant planet. The term "giant planet" typically refers to planets such as Jupiter, Saturn, Uranus, and Neptune, which are composed primarily of hydrogen and helium and have large sizes and low densities.

In contrast, stars are composed of primarily hydrogen and helium, but they are much denser and generate heat and light through nuclear fusion reactions in their cores. Even if a star were to stop fusion reactions, it would still retain its basic structure and not transform into a giant planet.

Additionally, the cooling process of a star would not be rapid enough for it to cool down to the temperatures and pressures necessary for it to become a giant planet. Instead, the cooling star would eventually become a white dwarf, which is a very dense, dimly-lit object that no longer produces light and heat through nuclear fusion.

prompter: Can you list the titles of some of the research papers on the subject so I can dive deeper in the details?

prompter: Can anything live on a white dwarf or is it still to hot? would I fall trough it if I stepped on it?

prompter: Okay, but in that case can a giant planet become a star?

assistant: 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.

prompter: How is a brown dwarf formed? What makes it different from other dwarf stars?

assistant: Brown dwarfs are formed along with stars by the contraction of gases and dust in a molecular cloud. However, unlike stars, brown dwarfs are not massive enough to ignite nuclear fusion and shine like stars. Brown dwarfs are typically composed of hydrogen and helium, but can also contain other elements like carbon, oxygen, and nitrogen. The mass of a brown dwarf determines its temperature, and the temperature affects its luminosity and color. Brown dwarfs with masses lower than 13 Jupiter masses (Mjup) cannot shine like stars, and are instead much cooler and fainter. This makes them difficult to observe and identify.

assistant: They are formed in the same way as stars and planets, namely by the gravitational collapse of a gas cloud. 

Unlike white dwarfs, brown dwarfs are protostars and not 'dead stars'. This makes them more like T Tauri stars, which are pre-main sequence stars and also have unstable burning phases for hydrogen.

assistant: 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: All dwarfs are not created equal.
A brown dwarf is formed through the same process as any other old star, through the gravitational collapse of a cloud of gas and dust. However, it is different from other dwarf stars because it doesn't have enough mass to sustain hydrogen fusion in its core, the process that powers stars. Brown dwarfs are intermediate in size between gas giant planets and low-mass stars, and have temperatures that are too cool to emit visible light, but can emit in infrared. As a result, they are often referred to as "failed stars."