Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 21/09/2012 12:26:17

Title: Could Enough Water Make A Water Star?
Post by: neilep on 21/09/2012 12:26:17
Water eh ?

It's like the best ever !...

Here's some.


* water.jpg (115.84 kB . 459x341 - viewed 10255 times)

luffley !



Say I had a big old load of water...about the size of our sun I guess it would be quite hot inside at the middle !...but the outside would not be so hot.......would it make a water star ?...

Some place somewhere there must be the most massive ball of water ever out there floating about....whajafink the mechanics of a star sized ball of water is like ?


Ta



Neil

Eau Water, Eau Water
Ewe Do No Falter
Ewe're There For Me
To Have A Dip
To Make Ice Pops
And To Sip
But Say Ewe Were
The Size Of Sun ?
How Would Ewe Be
Brightly Fun ?

Title: Re: Could Enough Water Make A Water Star?
Post by: syhprum on 21/09/2012 14:05:14
I cannot imagine 10^30 kg of H2O floating around in space but if it did what would be the effect of that vast amount of Oxygen on the start up of nuclear fusion that is required for a star to get going presumably the Oxygen would accumulate at the centre with an outer shell of Hydrogen but I doubt if pressures would be high enough for fusion to start up.
Title: Re: Could Enough Water Make A Water Star?
Post by: neilep on 21/09/2012 14:11:33
I cannot imagine 10^30 kg of H2O floating around in space but if it did what would be the effect of that vast amount of Oxygen on the start up of nuclear fusion that is required for a star to get going presumably the Oxygen would accumulate at the centre with an outer shell of Hydrogen but I doubt if pressures would be high enough for fusion to start up.

Thank you syhprum. Don't worry..I'll imagine it for you... [;)].............I guess I was just getting all hypothetical...though, one might think that with enough space and time many a strange event occurs. I appreciate your postulation.
Title: Re: Could Enough Water Make A Water Star?
Post by: CliffordK on 21/09/2012 18:28:08
The heat inside the star would also dissociate the hydrogen and oxygen.  So,  one would no longer have water.
Title: Re: Could Enough Water Make A Water Star?
Post by: syhprum on 21/09/2012 19:47:54
A central core of Oxygen is the state of very old and very massive stars shortly before they go supernova fusion only continues at very high pressures and temperatures.
Title: Re: Could Enough Water Make A Water Star?
Post by: yor_on on 22/09/2012 01:01:47
Cherenkov Radiation?
Title: Re: Could Enough Water Make A Water Star?
Post by: chris on 23/07/2017 10:29:23
I loved rediscovering this question from a few years back, so I'm bumping it for a reprise!
Title: Re: Could Enough Water Make A Water Star?
Post by: syhprum on 23/07/2017 21:43:50
I have no recollection of replying to this question but agree with what I said
Title: Re: Could Enough Water Make A Water Star?
Post by: Kryptid on 24/07/2017 01:55:09
Of relevance to this question: https://en.wikipedia.org/wiki/Oxygen-burning_process (https://en.wikipedia.org/wiki/Oxygen-burning_process)

For a ball of water the mass of the Sun, the extreme temperatures in the core would break down the water into oxygen and hydrogen plasma (as stated before). It would be too massive to be fully convective, so oxygen should accumulate in the core and hydrogen in an envelope around the oxygen. However, while the hydrogen and oxygen plasmas are still mixed, the hydrogen might be able to undergo fusion for a while (at least until the hydrogen migrates into the upper layers of the star). Once the hydrogen leaves the core, I think the star would be extinguished: the mass of this "star" would be insufficient to start oxygen fusion. The minimum mass required seems to be 8-9 solar masses. If it was of that mass, its oxygen would be used up in a maximum of five years, the time span becoming shorter as the mass increases (thus increasing core temperature and reaction rate).

Then again, the temperatures deep in the hydrogen envelope might still be enough to keep fusion going. I'm not sure. I guess I'd need to research more.
Title: Re: Could Enough Water Make A Water Star?
Post by: evan_au on 24/07/2017 12:13:49
There are some fairly massive balls of water out there in space - we call them comets.

Halley's comet is the best-known example of the class, and is currently about 15km long - it would have been even larger before it started touring the inner Solar system.

I am sure that much larger examples have condensed out of molecular gas clouds, and are lurking in the dark, out beyond the Kuiper belt.
Title: Re: Could Enough Water Make A Water Star?
Post by: MarcBlu on 26/07/2017 12:29:24
Wouldn't it turn into ice?
Title: Re: Could Enough Water Make A Water Star?
Post by: chiralSPO on 26/07/2017 16:37:15
Wouldn't it turn into ice?
There would likely be several phases of water (known and unknown) in such a scenario. Because the formation of such a body would likely involve a significant mass of water to "falling together," causing the temperature to rise substantially. But the pressures will also be extraordinarily high. There might be some unusual types of ices formed, if the thing doesn't heat all the way up to plasma and start fusing (or crush itself all the way to a black hole--I don't know how much water would be in a "star sized" body)

I would imagine that a lot of the water would be in some type of supercritical phase, as temperatures are likely to be above 374 C, and pressures would certainly exceed 22.064 MPa (3200 psia or 218 atm).

If the temperature exceeds 1100 C the water near the surface (lower pressure) might spontaneously break apart into H2 and O2, and the star could phase separate into the elements.
Title: Re: Could Enough Water Make A Water Star?
Post by: Bored chemist on 26/07/2017 16:54:33
It's an interesting question.
I guess it depends how we make this "star sized blob of water.
To make it easy, lets imagine that we start with a Earth sized blob.
It's not going to do any fusion or anything else that makes heat , so eventually it will cool down- some will evaporate and we will end up with a big lump of ice.
Now, imagine that , from time to time, someone turns up and drops a big bucket of water onto it.
Then they go away  and leave it to cool down again. Then they return with another bucketful.
As long as they do it slowly enough there's no reason for it to heat significantly.
From time to time you might get "blob-quakes as the inner layers are compressed into denser forms of ice.

If you made a star sized block of ice slowly enough  I'm not sure it would do anything.
Eventually you would get enough ice to collapse into a neutron star

Not sure how slow this would need to be- possibly longer than the age of the universe.
Title: Re: Could Enough Water Make A Water Star?
Post by: evan_au on 26/07/2017 22:55:38
Quote from: MarcBlu
Wouldn't it turn into ice?
Molecular gas clouds start with temperatures near absolute zero - around 10K, and not far above the Cosmic Microwave Background Radiation (2.7K). So a hypothetical water star would start as ice.

Once a molecular cloud has sufficient mass (a thousand to a million times the mass of the Sun), higher-density internal clumps can contract under their own gravity to form stars, planets, comets and asteroids. This is called a stellar nursery. Once the young stars start fusion, the temperature rises and the dust clouds dissipate.
 
The temperature has to be so low, otherwise the thermal motion of its atoms would cause the particles to drift away from each other before it could form particles as large as smoke particles.

In today's universe, the composition of the gas clouds is around 70% Hydrogen (left over from the big bang) and most of the rest is Helium (enriched beyond the 10% which formed in the big bang, by stars that have subsequently gone supernova). There are other impurities in these clouds, like carbon and oxygen, which were spewed into space when heavier stars went supernova; but the concentration is very low (<1%). When radio astronomers search for these gas clouds, they typically search for lines associated with molecules like carbon monoxide (CO).
See: https://en.wikipedia.org/wiki/Star_formation#Interstellar_clouds

Why Water Stars Don't Form
The composition of these clouds is mostly hydrogen & helium. If you put a large amount of these together, you will get hydrogen fusion - a bright star; there is not enough oxygen to form a water star.

However, water has a very high melting point (roughly 273K), so you could imagine that as the molecular cloud near a new star heats up, any wisps of hydrogen, helium, oxygen and nitrogen will be evaporated and driven away by the stellar wind of the young star. However, high melting-point molecules like water, CO2, graphite and NH3 could clump together to form comets - a "dirty snowball".
 
These are necessarily smallish objects, as any large objects would have enough gravity to hold onto their hydrogen, helium, oxygen & nitrogen, forming a gas giant.
See: https://en.wikipedia.org/wiki/Accretion_(astrophysics)#Accretion_of_comets

Diamond Stars?
If you want to get romantic, it is thought that stars a bit more massive than the Sun could burn most of their Hydrogen & Helium to Carbon, but not have enough mass to carry fusion any further (ie not produce much oxygen).

These stars would cool down over billions of years, forming a white dwarf which really is "like a diamond in the sky". 
https://en.wikipedia.org/wiki/Carbon_star#Astrophysical_mechanisms
Title: Re: Could Enough Water Make A Water Star?
Post by: Monox D. I-Fly on 07/03/2018 03:04:09
There are some fairly massive balls of water out there in space - we call them comets.

Huh? Never knew that comets are made of water. I thought comets are hot since I think of them as shooting stars, or are those water boiling?
Title: Re: Could Enough Water Make A Water Star?
Post by: Kryptid on 07/03/2018 05:05:05
Huh? Never knew that comets are made of water. I thought comets are hot since I think of them as shooting stars, or are those water boiling?

Shooting stars are actually meteors that give off light as they burn up in the atmosphere. Even though you can see their light from the ground, they can be very tiny (the size of sand grain, for example).
Title: Re: Could Enough Water Make A Water Star?
Post by: EatonEbenezer on 09/03/2018 14:32:25
Impressive!
Title: Re: Could Enough Water Make A Water Star?
Post by: Recrudesce on 17/03/2018 21:01:28
Neil, my fluffy fun friend, any fire that started would surely be put back out by all that water  ??? ::)