Jupiter is so massive, that the barycenter of the Sun-Jupiter system (and indeed the whole solar system) is outside the surface of the Sun. This despite the Sun being a thousand times as massive.
There are a bunch of physical laws in play here. In the end, it is mostly about Conservation of Energy. One form of energy is angular momentum. In a closed system, we can expect Conservation of Angular Momentum - add up all the bits of matter, take into account their mass, their distance from the center of rotation, and their speed, and that should remain constant. So... the angular momentum we see in the Solar System today is close to that of when it was formed. There will be differences because the Solar System isn't a 100% closed system - stars have passed nearby in the past, etc - but the general idea holds. Also, some angular momentum can be converted into heat when orbiting bodies flex and stretch - this is why Io is such a volcanically active body. Anyway, we should have never been surprised that exoplanets exist. In the star formation process, clouds collapse into stars, but because the clouds are so big they will have a certain amount of angular momentum resulting in a relatively fast-spinning star. It is the same idea that makes a spinning skater spin faster when he/she pulls his/her arms in tight. Anyway, there is so much angular momentum in a dust-cloud a light-year across that if you were to scrunch it all into one body, it may very well spin so fast that the body would fly apart. One way around this is that there are small bits of matter orbiting the star, holding a large amount of angular momentum, thus preventing the star from flying apart. These bodies simply have too much orbital energy to have ever gotten close enough to the star to get gobbled up. THAT'S why we have planets and exoplanets.
I found this little tidbit:
Jupiter has most of the rest of the mass of the Solar System and it is five times as far from the Sun as the Earth. As a result it actually has almost 60% of the Solar System's angular momentum.
Amazing that Jupiter is a small fraction of the Sun's mass, yet it holds most of the angular momentum of the Solar System. Seems counter-intuitive that a small piece of star-schmaltz (Jupiter) holds so much energy in the Solar System. We should expect similar circumstances at other stars.
FWIW, this is highly simplified and the complicated stuff is the devil-in-the-details, but the basic message holds pretty well.
Edited by Sleep Deprived, 16 September 2020 - 07:20 PM.