[Petrochemicals (OP)]

As the title says, if star formation is a spinning disk of matter gratually becoming faster and denser at the core to a critital mass to enable gravitational fusing of atoms, and planets are formed in the leftovers of the spinning disk, by collisions and gravitational critical masses to large spherical form, why do so many stars lack the existance of planets ?

[RD]

... why do so many stars lack the existance of planets ? ...

Exo-planets are difficult to detect ... https://www.space.com/24894-exoplanets-habitable-zone-red-dwarfs.html

[SeanB]

With the number detected recently, it seems that pretty much every star will have a planet or two around it, and systems consisting only of a star and nothing else will be very rare, probably only something that occurs in close binary systems, where the 2 stars rotate around a common centre of gravity that makes any close in orbits unstable, though you will find that there will be planets at a distance where the effect of the 2 masses revolving around each other can approximate to a point source.

About the only stars that will not have planets are those that were supermassive, and which went bang as a supernova, vaporising any close in planets in doing so. Even those will have  far placed outer planets that would have survived the cooking, though the gas giants would be much smaller from having the majority of gas boiled off.

[evan_au]

why do so few stars have planets ?

I think this might be the wrong question. A more appropriate question would be "Why have we detected so few planets around other stars?"

Many of the exoplanets detected in recent years were from the Kepler mission, using the transit method.
- This only works if the planet passes on a direct line of sight between the Earth and the far star
- If we assume that planetary orbits are aligned randomly, only a very small fraction of planets will intersect this direct line of sight.
- So astronomers have to extrapolate from the number of exoplanets detected to the numbers that actually exist
- This predicts that there will be exoplanets around most stars
- Kepler has to see 3 transits to declare an exoplanet. Unfortunately, the mission was cut short by equipment failure. So the mission would only be able to detect planets with orbits out to about 1 year. This would have missed almost all the planetary mass of our solar system.

It is thought that there may also be a lot of planets cast out of unstable early planetary systems, and are now free-floating.

[Petrochemicals (OP)]

I think you are right by the reasoning of detection. Im pleased anyway as george lucas's "Starwars universe" is intact, which is what raised the question in the first place. The media has its part in playing out my understanding of the universe, it would be better if the common understanding was all stars have planets, and most with an earth.

That brings me to another thought, if planitary formation comes about through circulation, and you have 3? Types of stars (small medium and large) around stars such as our sun (fairly common) do all planitary formations follow a set procedure, ie my very educated mother just served us nine, in that composit mass sequence, ie small planets close getting bigger then smaller, asteroids ,gas giants and then the plutonian area ?

I did find another naked science post in the meantime, just its very difficul5 to pin down, the monikas, -stars planets - arise more than a few times !

[evan_au]

its very difficult to pin down, the monikas, -stars planets - arise more than a few times !

You could start here:
https://en.wikipedia.org/wiki/Protoplanetary_disk

[puppypower]

I think you are right by the reasoning of detection. Im pleased anyway as george lucas's "Starwars universe" is intact, which is what raised the question in the first place. The media has its part in playing out my understanding of the universe, it would be better if the common understanding was all stars have planets, and most with an earth.

That brings me to another thought, if planitary formation comes about through circulation, and you have 3? Types of stars (small medium and large) around stars such as our sun (fairly common) do all planitary formations follow a set procedure, ie my very educated mother just served us nine, in that composit mass sequence, ie small planets close getting bigger then smaller, asteroids ,gas giants and then the plutonian area ?

I did find another naked science post in the meantime, just its very difficul5 to pin down, the monikas, -stars planets - arise more than a few times !

Based on way the stars are arranged in our solar system; small rocky planets, then an asteroid belt, then gaseous giants, then smaller rocky Pluto type planets, suggests a first generation star exploded, but it was not a super nova scale explosion. It was a more limited and controlled explosion, such that the debris field profile would be based on the weight/mass of the materials ejected; heavy metals and oxides would stay closer, while lighter gases would be propelled much further, with some overlap.

It makes no sense that stars have to either burn out or have to go nova or super nova, with nothing in the middle. It makes more logical sense that star could also explode in the middle of this range, making planets and then also reforming as a secondary generation star. If the star reforms too fast, there will be no planets. If it reforms to slow there will be too many planets, causing orbital collisions especially at the solid-gas transition zone.

We also have the two contemporary extremes which if the star burns out no planets will form and if it goes supernova even a second generation will take time to form.

[evan_au]

you have 3? Types of stars (small medium and large)

I am sure astronomers would have more categories, but I guess you could say "small, medium and large" stars is a good start.
- Small stars: Stars much smaller than the Sun (eg Proxima Centauri) are Red Dwarfs, which will never produce any elements heavier than Helium, and will never enter a Red Giant phase, but will continue glowing for trillions of years after the Sun has become a white dwarf.
- Medium Stars: Stars like the Sun (eg Alpha Centauri), are unlikely to burn elements heavier than Helium, but stars slightly more massive stars will produce elements like Carbon, Nitrogen & Oxygen in their core (important for life on Earth). These end up shrinking into a white Dwarf star when they burn all their fuel.
- Large Stars: Larger stars (like Betelgeuse) will produce elements up to Iron (an important ingredient in the core of planets). These large stars usually end up exploding as a supernova, producing a neutron star or black hole.
See: https://en.wikipedia.org/wiki/Stellar_evolution

It makes no sense that stars have to either burn out or have to go nova or super nova, with nothing in the middle...a more limited and controlled explosion

Medium and Large stars starting to burn elements heavier than Hydrogen enter a "Red Giant" phase, during which they puff off some of their outer envelope, forming a planetary nebula. I guess you could call this a more gentle, gradual, "intermediate - sized explosion", sometimes continuing for millions of years. (Note:A planetary nebula is not itself a series of planets, and is too hot to form planets.)

The elements emitted from the Red Giant or Supernova enrich the interstellar medium (mostly Hydrogen & Helium from the Big Bang) with heavier elements formed by nuclear fusion in the star. Which elements are released depends on the size of the star (see above).

But beyond the Red Giant phase, individual stars will either shrink to a form White Dwarf, or explode to form a Neutron Star or Black Hole; for individual stars, the ultimate fate is fairly binary.

On the other hand, Binary stars can be more complicated, for example, a white dwarf can undergo a nova explosion...
See: https://en.wikipedia.org/wiki/Planetary_nebula#Role_in_galactic_enrichment

the debris field profile would be based on the weight/mass of the materials ejected; heavy metals and oxides would stay closer, while lighter gases would be propelled much further, with some overlap.

This sounds somewhat similar to the current popular theory about planetary system formation.

There is one significant difference: The gas and dust released by a Red Giant or Supernova must exceed the escape velocity of the star, or it will simply fall back into the White Dwarf, Red Giant, Neutron Star or Black Hole; if it falls back in, it will not form planets.

So the main theory is that the elements released by a star find their way into molecular dust clouds, which are far from the original star. They cool, and become cold and dense enough to form another generation of stars (and their planets).   
See: https://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System#Formation_of_the_planets

[Petrochemicals (OP)]

I think you are right by the reasoning of detection. Im pleased anyway as george lucas's "Starwars universe" is intact, which is what raised the question in the first place. The media has its part in playing out my understanding of the universe, it would be better if the common understanding was all stars have planets, and most with an earth.

That brings me to another thought, if planitary formation comes about through circulation, and you have 3? Types of stars (small medium and large) around stars such as our sun (fairly common) do all planitary formations follow a set procedure, ie my very educated mother just served us nine, in that composit mass sequence, ie small planets close getting bigger then smaller, asteroids ,gas giants and then the plutonian area ?

I did find another naked science post in the meantime, just its very difficul5 to pin down, the monikas, -stars planets - arise more than a few times !

Based on way the stars are arranged in our solar system; small rocky planets, then an asteroid belt, then gaseous giants, then smaller rocky Pluto type planets, suggests a first generation star exploded, but it was not a super nova scale explosion. It was a more limited and controlled explosion, such that the debris field profile would be based on the weight/mass of the materials ejected; heavy metals and oxides would stay closer, while lighter gases would be propelled much further, with some overlap.

It makes no sense that stars have to either burn out or have to go nova or super nova, with nothing in the middle. It makes more logical sense that star could also explode in the middle of this range, making planets and then also reforming as a secondary generation star. If the star reforms too fast, there will be no planets. If it reforms to slow there will be too many planets, causing orbital collisions especially at the solid-gas transition zone.

We also have the two contemporary extremes which if the star burns out no planets will form and if it goes supernova even a second generation will take time to form.

That does explain why at least 4 planets  have heavy elements already, i had not thought of why the stellar cloud rotation would have left heavier elements so far out.

And with the radiation coming off jupiter you would hqve to say a heavy element core to it too?