Giant planet systems.

Nothing of this nature has even been viewed and I doubt you will find anything in any solar system that will match or exceed the size of its sun.

If you mean that there is no star, physically it would be possible, but I don't know if astronomically it would ever occur. Is your question, "Do any brown dwarfs have satellites?"

I think patiodog is correct. It is possible there are billions of systems in our galaxy more or less like our solar system, except the cental 'sun' did not have enough mass to start nuclear fusion. We can not yet detect such systems (if any) more than a few lightyears away. Neil

Jupiter and Saturn, for example, are giant gas balls that never quite made it to become suns.

If a system has a star and a giant planet, then the planet will orbit the star because the star will be more massive.

{strictly speaking both bodies orbit around their common centre of mass}

Conversely if the star was to orbit the "planet" it would mean the "planet" was more massive than the star and therefore it would itself switch on to become a star. So you would have a binary star system.

I think the answer to your question is no. But the more extra solar planets we find, the stranger the Universe becomes.

Re: Giant planet systems.


No, but this is only because of definitions. A "star" is generally considered to be a lit massive body undergoing some type of atomic energy generation process. And a planet is a massive body which is in orbit around a "star".



Yes, the configuration is definitely possible. All you need is an orbital system in which the central star doesn't acquire enough mass to ignite and you get a system of this type.

In a more general sense though, every planet with a moon (or moons) is the type of system you describe. For instance, Jupiter could be considered a "solar" system from a gravitational point of view. Jupiter generates a lot of heat, so it could almost be considered a brown dwarf (it all depends on your definitions).

However, as you noted above, it all comes down to terminology. If a "solar" system is defined as a group of bodies orbiting a "lit" star, then a planet as a center point doesn't qualify.

Protosystems all start with central points which have not yet accumulated enough mass to start a fusion process in the new star, so you could also say that all systems start in the configuration you describe.

Re: Giant planet systems.

There are at least 4 systems of this nature in our own neighbourhood.
The Jupiter, Saturn, Uranus and Neptuninan systems are as described with a massive body in the centre that isn't a star with lots of little planets all orbiting it.
If you're talking about a 'failed star' then jupiter isn't really big enough. It would require about 10 times as much mass to become a Brown Dwarf even though it does in fact emit more energy than it receives from the Sun.
There are many Brown dwarf 'stars' out there that have been discovered using advanced infra-red telescopes. Whether any of them have planets is not known at this time.

Is mass all that is required to become a star? I mean, if there were a planet the size of the sun would it "ignite" regardless of the elements of which it is composed?

Presumably it's gotta be mostly hydrogen -- but it's hard to imagine a ball of gas that big that isn't...

But I know very little about this stuff...

Patio is basically right. Though it's possible to accumulate a large quantity of heavy elements sufficient for the mass to lead to self fusion, it's unlikely, and not the usual way a star forms.

Normally, a star forms from a primordial cloud of mostly lighter elements (Hydrogen and Helium). First generation stars would be made exclusively of lighter elements because that was all that existed to form them. But the evolution of stars themselves lead to heavy elements, the dispersal of which results from supernovas.

Our own star is thought to be a third generation star, which means that it is a collection of debris from the explosion of at least two stars before it. The composition of a star, plus its size and age, give some indication of its generation. Our Sun is partially composed of heavy elements which could not have been produced by the star itself, so it must be an accumulation of those elements which were the result of previous Supernovae. Likewise, the planets (including Earth) which orbit the Sun are a result of the debris from previous Supernovae (heavy elements can only be formed in this way).

The carbon and calcium atoms which make up your body can only be produced at the core of stars during their maturation process, and only Supernovae can release these atoms to later be formed into planets and other stars.

Carl Sagan said "we are made of Star Suff", and it sounds like a tedious cliche, but it isn't. It's literally true; a diamond of truth hiding amidst the rinestones of poetic tedium.

Ros is it just the concentration of heavier elements that define 2 or 3rd generation stars? Are there any 4th generation stars about, and how do we know the Sun isnt one?

Pretty much yes.
It really is all down to mass.
Primarily stars are made of hydrogen but that's only because that was what was formed in the big bang.
If you did have a ball of rock the size of the Sun then there would be more than enough pressure in the interior to ignite the atoms there into nuclear fusion.

If you had a planet like Earth though with the iron core then you run into a different situation.
With iron it takes more energy to fuse the atoms together than the fusion releases so you'd need a net input of energy for normal fusion. So it's not going to happen in most parts of the iron core.
The outer parts of the "planet" (the outer parts of the core) that are made of rock etc... however will be under enough pressure to fuse and release energy.

In the deep interior a rough calculation shows that there is more then enough pressure considering the amount of mass you have in this enormous "planet" to enable the core to become degenerate.
This is where all the electrons get shoved into the protons and become neutrons because the gravitational pressure of all that overlying mass overcomes the electrical repulsion that keeps elecrtons from crashing into protons normally. This releases a collossal amount of energy which would almost certainly blow the whole thing to bits but assuming it didn't you'd have a neutron matter core surrounded by almost degenerate matter undergoing intense heating from the fusing outter core. This would force more and more matter to become degenerate and so the degenerate core would grow, releasing more energy as it went as more matter gets pressed down onto it.
The whole thing would basically melt in a very short period as we watched it and then there would be the most amazing explosion as the energy released by the formation of the neutron matter at the core formed.

Personally I'd be watching all of this from a perfectly black spaceship orbiting a completely different star while my friend Hotblack Desiato played his most recent composition on the stereo.

Boy meets girl and falls in love under a moon that then explodes for no apparent reason? That composition?

LOL !!
Yeah ! That's the one !

Depending on who's definition you use, a star's "generation" is defined by how many stars came before it to create the matter from which it is formed, or by what level of atomic fusion is currently supporting its gravity, or by its composition.

The type of generation I was talking about is how many other stars came before it to create the elements which now compose it.

When super giant stars explode, they can release enough matter to form many smaller stars and solar systems. These stars in turn can explode to form still others. Each formation event would be a generation.

However, to complicate things, material from other massive explosions can get mixed together, so it's hard to tell just from the composition how many stars went into the formation of another one.

Here are some links:

http://www.solarviews.com/eng/starformation.htm

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961112a.html

That our sun is third generation is not written in stone.

If most of the first and 2nd generation nearby stars were slightly more massive than our Sun is now then third generation is correct, assuming current theories are mostly correct, which is optimistic, IMHO.
If so we have to wonder where are the nearby white dwarf stars? By now they would have cooled to 100 degrees K = minus 173 C and thus would be almost undetectable more than a light year away. Perhaps there are more white dwarfs nearby than visible stars? Neil

If most of the nearby first, 2nd and third generation stars were type F = 2 or 3 times more massive than our Sun is now, then our Sun is mostly 4th and 5th generation. If so where are the nearby neutron stars? All around us, perhaps, as they are by now so cold they are almost undetectable more than a light year away. Neil

The lack of nearby compact stars argues that Our Sun is 2nd generation that just happened to get more than it's share of heavy elements from a nearby first generation super nova. Neil