Completely ridiculous question, but I'm half sort of writing a sci-fi/fantasy series, and a set piece I always wanted to include is the fulfilment of a prophecy in which a red dwarf sun is brought into the orbit of supermassive ocean world, then dropped into the waves. My question is what would happen? Would it go out? Would it continue to burn under its own energy even for a small time? Tangentially what would the ridiculously huge amount of steam produced do to the planet at large? Obviously the science involved is not physically sound- in terms of finding a planet that big covered in water, or the ability to shift suns, so don't tell me how stupid it is:P I'm simply trying to comprehend what would happen if, and what a sun drowning would look like....

Wouldn't the water evaporate even before the sun got close enough to touch it. As I believe the sun is more like nuclear reactions than a camp fire. Not sure about the steam. Perhaps the planet would resemble a comet's tail as the planet shrinks due to massive water loss.

Also the bigger issue is about the sun's gravitational pull. It would destroy the planet before it could be pulled into the sun. If it was, it would probably show up as a solar flare. The planet couldn't be larger than the sun as the immense gravitational pressure will turn it into a sun. Though I adore astronomy (I'm fascinated by the life cycles of stars and the variations like pulsars and other neat stuff), my forte is history so I can't speak in greater depth about all this.

The water wouldnt get anywhere near it. It would turn to steam probably thousands of miles before touching the sun. It would probably look something like a crater in the ocean. With the sun in the centre.

So we're going with the sun would definitely be able to withstand it and continue through its own fission and simply burn out the ocean around it... cool:P Would the sudden transition to steam be able to act as a massive power source?

You have two bodies which remain spherical under their own weight. Stick them together and they won't stay as two distinct spheres anymore. Drop the one onto the other and it'll make a hell of a bang and splatter around everywhere rather than sink quietly beneath the waves.

It would be interesting to see what happens if you get a body of water larger than a star and leave it to compress under its own weight, though.

If a Sun can burn in the vacuum of space, where there's no air, no oxygen, nothing... then it can burn underwater.

Gennaroc:
So we're going with the sun would definitely be able to withstand it and continue through its own fission and simply burn out the ocean around it... cool:P Would the sudden transition to steam be able to act as a massive power source?

For inhabitants of the planet, yes they could suddenly become steampunk. You'd have to make them technologically advanced enough to either know that this was about to happen, so they could majorly heat-proof their houses, or so that they can just fly off in a spaceship or something.

I agree with the above people that water will be evaporate therefore for a sun to still be burning underwater I think the impossible/ irregular logic is needed.
I only voted yes because of the off side idea that maybe this "water" doesn't evaporate or maybe the sun isn' that hot enought to evaporate the sun.

Now I'm no science genius, but from what I know of physics, unless that planet is larger than the star, which is a physics nightmare on it's own, then the planet would essentially stop existing and just bemore mass of the star. A red dwarf would be evaporating all the water on the planet from millions of kilometres away, in actual contact with the planet? All liquid on the planet boils, all rock on the planet melts, basically everything on that planet would be destroyed. And this is only accounting for the heat from the star, ignoring the gravity and the fusion.

maddawg IAJI:
You ever see Mercury lately? Ya, an average day on it can go up to about 427 C and that's with millions of miles of distance between the sun and the planet.

Planets aren't heated up by the sun being hot, they are heated up by the EM radiation it emits. Heat can't transfer through a vacuum.

OT: Yeah, the sun's massive gravitational pull would probably drag in the planet as well, as it is such a dense object. The reason it's so hot is because originally it had such a large mass that fusion began to happen due to the shear amount of force on all of the particles within it.

Gennaroc:
snip

The sun would actually get hotter. I know it seems counter-intuitive but it's true.
You have to remember there are no "chemical" reactions going on in the sun, only nuclear. It is not on fire.
Fire works like this. In general
Element+Oxygen+Energy->Elementoxide+more energy.
if you smother ^this energy. Or prevent the Oxygen reaching the fuel. the fire stops, no more energy released.

Nuclear fusion works like this
Light Nucleus+Light nucleus+pressure=heavier nucleus+a fuckton of energy.
Nothing you can do can smother a a nuclear fusion. It would only add to the pressure. Add to that Water being H20, and Hydrogen being the easiest element to undergo fusion, you are literally piling fuel onto the fire (i mean fusion)

also the suns gravity would pull more water to it, compounding the problem

I have TWO solutions/suggesions for you

Research something called a "Y-dwarf" they are small, light, relatively cool stars (it has been suggested (though it is unlikely), that they could be as cold as the human body).
This could NOT be the primary star in a system, it is not massive enough.

The planet it is set on could be what is called subgiant planet, something like Uranus or Neptune. This would allow it to have very deep, very warm oceans.
If the planet is populated by natives give them exceptionally gravity resistant bodies.
If it is colonised use some SF tech that allow everything to resist the extra gravity.

The effects would be

A HUGE increase in global warming. Water vapour is acutally one of the worst greenhouse gases on earth.
Holy shit i just hought of something really cool...BRB MS Paint becons!!

sources: the first year of my physics degree. Some geography i had to study and hate

and probably take Alan Moore's advice over mine, "keep the science accurate as long as it fits the story. if the science doesn't fit the story...fuck the science"~huge paraphrasing here.

Doitpow:

Gennaroc:
snip

Holy shit i just hought of something really cool...BRB MS Paint becons!!

Remebered I can't do paint for shit. I'll try to describe it.

basically on one side of the planet you have the sun, bascally stuck to the ocean floor, boiling all the ocean, this turns to vapour, rises in the atmosphere and is caught in a high altitude jetstream which transports it to the other side off the planet, where it condenses into constant tropical storms. the water produced flows around the planet to the sun...repeat ad infinitum.
one side of the planet is now a mass of boiling ocean, the other a constant typhoon. there might be a habitable "band" between the two.

The sea however would constantly be dropping in level, as more hydrogne and oxygen are stripped out of the cycle into the sun, which is growing in mass.

more and more land would be being revealed as the sea level drops...maybe theres some ruins of an ancient civilisation there or something?

you have a countdown basically untill all the water is gone or the star gains the necessary mass to tear the planet to bits or simply burn it to nothingness.

woot
there is some soft hypothetical science for you. My earth science lecturing is facepalming in shame

The only reason normal fire doesn't burn underwater is because there's no oxygen to fuel the fire. But since there's no oxygen in space either, and the sun still "burns", which is actually more like smashing atoms together at insane speeds, releasing radiation, it would burn in water too. If you can find enough water, that is, and put the star in it before it all evaporates.

The water would boil away before it even got close. There is no way this is possible. Also, the amount of water needed would be massive, exponentially larger than the total water of earth.

There are too many variables and possibilities For me to go into this without going into a huge scientific debate with myself that would take forever to retype here.(and I don't feel like doing that at the moment) In the end, because it's your sci-fi series, you could make it so that a sun could go into the ocean and tap dance with the fish for all you care.

Gennaroc:
Completely ridiculous question, but I'm half sort of writing a sci-fi/fantasy series, and a set piece I always wanted to include is the fulfilment of a prophecy in which a red dwarf sun is brought into the orbit of supermassive ocean world, then dropped into the waves. My question is what would happen? Would it go out? Would it continue to burn under its own energy even for a small time? Tangentially what would the ridiculously huge amount of steam produced do to the planet at large? Obviously the science involved is not physically sound- in terms of finding a planet that big covered in water, or the ability to shift suns, so don't tell me how stupid it is:P I'm simply trying to comprehend what would happen if, and what a sun drowning would look like....

As a red dwarf is gas(alot of gas but still gas) it would behave like any object getting pulled into a larger gravitation field(just look up videos of black holes eating stars and you would have a rough idea).

The star would string out and just feed into the atmosphere. Mind you the gas is still 4000*k so the water would boil off and break down quite easily(assuming the planet is made up of things denser then iron and would not cause the pull of gravity to turn the planet into a neutron star) i guess the planet would eventually have water again in a few billion or so years

That being said you might as well write anything you want you somehow already have a planet that is larger then most of the stars in this galaxy that has the mass and material to fuse but yet is not and was not in the past to the point it can support water so you left reality long ago.

I don't see why fusion shouldn't be able to occur under water. You need to remember that stars don't "burn" as such. The water might even provide a handy source of hydrogen to fuel the fusion.

There are two problems though:
1. Lots of water will evaporate. Depending on the scale of things, there could be various effects of this. It would most likely look like a giant explosion though, and cause huge tsunamis and whatnot.
When the star is submerged in the water, a large coulumn of water vapor will certainly be a permanent fixture at the point above where the star is submerged. Lots of steam would rise into the atmoshphere of the ocean world and cause greater amounts of rain. The winds in the areas near the submersion-point will all move in the direction of the coulumn of steam.
Lots of other implications as well.

2. The fusion of the star might set off a chain reaction and cause fusion to occur throughout the entire ocean, thus turning said ocean world into a burning hell. Basically a new star.

This is all coming from a layman though, so it could be I'm wrong.

Technically speaking, a sun doesn't 'burn'. So, yes, it would keep doing what it does now. What happens to the water is another thing. Probably evaporate and rapidly expand, pushing away all remaining water to the outside.

If the star is active, then it has enough gravity to induce fusion. The heat it produces would evaporate the water, but I think that most of the vapor would be captured by the star's gravity. Therefore, it would most likely draw the water into itself, break it down into hydrogen and oxygen, and use the two elements as fuel. As it does this, the added mass will increase its gravitational field, causing it to draw in more and more of the planet and making it capable of fusing heavier elements. In the end, I believe the most likely outcome would be that the star eventually consumes the entire planet as fuel.

This is all wrong. See the post below.

cerealnmuffin:
The planet couldn't be larger than the sun as the immense gravitational pressure will turn it into a sun.

Wait, this guy's right. The smallest known star is still larger than the largest known rocky planet. Gas giants can be larger, but then it wouldn't be a water world. The gravitational pull of a rocky planet of that size would cause it to collapse into itself and undergo stellar fusion. Any body of water large enough to contain a star would have enough mass to become a star itself.

The sun could not burn underwater because there would BE NO WATER.
I don't think you fully grasp how GODDAMN HOT a sun is.

I don't how big this planet of yours might be, but i think a red dwarf would still have a diameter of 10^5 kilometer.
And it would be 2200 kelvin hot.
You could go with a brown dwarf, which would be smaller but i don't know how small.

Amaror:
I don't how big this planet of yours might be, but i think a red dwarf would still have a diameter of 10^5 kilometer.
And it would be 2200 kelvin hot.
You could go with a brown dwarf, which would be smaller but i don't know how small.

Brown dwarves aren't actually stars. They are supermassive gas giant planets that almost have enough mass to initiate fusion, but not enough.

It wouldn't be doused if that's the question. Its not a fire in the normal sense, its a nuclear reaction. This is more like asking if a nuclear bomb can detonate underwater.

The water would be steam long before it hit the star, but that vapor would get sucked in. Then, I see 2 things happening based on adding raw material to the star.

1, the added hydrogen would fuel the suns reaction. I think. Im not sure if the sun, given infinate material, would grow or if it would simply take longer to exhaust its fuel. With all that fusion going on, and an influx of material, its probably destined to be a black hole assuming infinate water.

2, maybe that hydrogen is not useable in water form, or maybe the oxygen gums up the stars reaction, and the star burns out. I believe It would become a brown dwarf in this case.

Look up stars Main Sequence for ideas on this, how they evolve based on the materials they contain. But for a nifty, reality ignoring science fantasy approach, you could say that the star slowly grows (or rapidly by star standards). And threatens to become a black hole at any moment. Just remember that functionally, water on a star wouldn't dose anything. What your really doing is adding material to the reaction.

it's also possible that the water would be not only evapourated but absorbed into the massive fission reactions on the surface of the star, depends on the type of star though... you could end up with said planet becoming engulfed in a newly refuelled star... Can't tell 'till we actually see such an occurance though... doubt that water would put out a star, due to the nature of a star's "fire" not being just fire, but a constant fission/fusion reaction burning tens of thousands of degrees centigrade on the surface, and much, much hotter near the core, in the vaccuum of space...

no, because the water would be instantly turned into steam, and also because star's don't technically "burn" if they did our own sun would have burnt out a few thousand years ago, they fuse a pair Hydrogen atoms into helium, the mass that is lost in this fusion is released as a f-load of energy. if we could achieve this nuclear fusion to the same efficiency as the sun, we could supply the entire electrical needs of the UK with a pint of seawater (not sure for how long though)

I think you left the reality of science a long time ago and just write whatever the fuck you like.

Axolotl:
All liquid on the planet boils, all rock on the planet melts, basically everthong on that planet would be destroyed.

God no, not the thongs!

Water would have no effect on a sun, it's a nuclear reaction as a result of pressure, not a combustion from heat and O2. Water, on the other hand would evaporate and be broken down into H2 and O2 from the heat, and pulled into the sun from gravity. I don't know much about stars, but if a red giant crashed into a water planet, I'm pretty sure it would de-age it, because of all the hydrogen, but it would take a long time for the H2 to get to the center, so it wouldn't de-age it for a long time.f

However, you're writing a sci-fi/fantasy book, do what you want, ignore realism if you have to.