I had to look this up so I got this from NASA's site:
Every 238 years, the orbits of Neptune and Pluto change making Neptune at times the farthest planet from the sun.
Hubble confirms new dark spot on Neptune
New images confirm the presence of a dark vortex on Neptune. Though similar features were seen during the Voyager 2 flyby of NASA's Hubble Space Telescope in 1989 and by Hubble in 1994, this vortex is the first one observed on Neptune in the 21st century. Ref. Source 4z.
Being a large gas giant does not always mean they can be a sun. The composition of Neptune is primarily Methane. I do not think that will sustain a long lived star like burn. I think the other two Saturn and Jupiter have the wrong mix of gasses to burn like a sun.