Gas giant planets do not star. They are giant planets, composed primarily of gas, such as hydrogen and helium, with a relatively small rocky core. While they are massive, they lack the sufficient mass and internal pressure needed to trigger nuclear fusion, the process that powers stars.

Here's a breakdown of why gas giants aren't stars:

* Mass: To become a star, a celestial object needs to be massive enough for its own gravity to compress its core to the point where nuclear fusion can occur. Gas giants, while large, are far less massive than stars.

* Nuclear Fusion: Stars generate energy by fusing hydrogen atoms into helium. This process requires incredibly high temperatures and pressure found in the core of a star. Gas giants don't have the internal heat and pressure needed for fusion.

* Structure: Stars are mostly made of plasma, a superheated state of matter where electrons are stripped from atoms. Gas giants, while mostly gas, are not hot enough for this to occur.

In short, gas giant planets are huge, but they are still planets, not stars. They lack the necessary mass and internal conditions to ignite nuclear fusion.