9
$\begingroup$

The question is a bit unrealistic with its circumstances but lets assume there is a bucket of ice cooled down to about absolute zero and is about 1000 km away (all around the sun) from sun and moving with v_0 = 1000km/sec, what will be if that all water with mass of sun reaches the sun.

UPDATE

Basically I have read about this in gizmodo http://gizmodo.com/could-the-sun-be-extinguished-by-a-bucket-of-water-just-1669914928 but did not agreed , thats why I have decided to ask about this phenomena here, hoping to find out more precise answer

$\endgroup$
  • $\begingroup$ That's a big bucket of ice, friend! $\endgroup$ – CuriousOne May 12 '15 at 9:23
  • $\begingroup$ do you mean what will happen if we got a mass of ice equal to the mass of the sun cooled to 0K and 'poured' it onto the sun? $\endgroup$ – ziggy May 12 '15 at 9:24
  • $\begingroup$ @ziggy, yes I mean actually what you wrote. BTW I wrote "about absolute zero" $\endgroup$ – Aram Tadevosyan May 12 '15 at 9:28
  • 16
    $\begingroup$ Have you already asked at the one suitable place for this sort of a question? $\endgroup$ – Pavel May 12 '15 at 16:05
  • 2
    $\begingroup$ How would you keep that much mass at absolute zero? The gravity would collapse the core into plasma, and probably after a while it would be as hot as any star on the surface. $\endgroup$ – Superbest May 12 '15 at 22:45
11
$\begingroup$

This would be a highly energenic event, a gravitational collapse in combination with the initial inward velocity of 1000km/s (which is greater than the escape velocity at the surface of the sun).

There would be some type of nova event initially because the hydrogen already present in the sun would be compressed by the infalling new material, greatly enhancing fusion. Some material may be ejected and become a nebula in the nova event; rebouding energy would be a factor in addition to enhanced fusion, as in a core collapse supernova.

The water would dissociate into atomic hydrogen and oxygen.

Of the material not ejected in the nova event, the oxygen would eventually form a core at the center of a star, with lighter elements (H, He) being a shell around the core.

What happens from there depends upon the mass remaining.

If the remaining mass is less than 1.39 solar masses (the Chandrasekhar limit), the star would eventually become an inert white dwarf star, with the oxygen core being sustained by electron degeneracy pressure and unable to undergo oxygen fusion. If more than 1.39 solar mass remain, the star could become a neutron star.

$\endgroup$
  • 2
    $\begingroup$ Are you sure that oxygen can reach the core so fast? Most of the star is not convective, so the only way to reach the core is by brownian motion. I roughly estimated that it will take $10^{24}$ seconds ($10^{16}$ years) to travel at a distance of a solar radius, but that is much more than the estimated lifetime of the Sun and the particle can travel that distance in any direction inside the Sun. $\endgroup$ – GRB May 12 '15 at 17:58
  • 1
    $\begingroup$ This seems to be largely speculation. Has anyone done a calculation for a 2 solar mass star that is ~50% metals? @MFH gravitational settling can be highly effective in radiative zones. However, radiative forces would oppose the settling of oxygen from the outer layers. $\endgroup$ – Rob Jeffries May 12 '15 at 18:10
  • 1
    $\begingroup$ @MFH It should fall very rapid at first because the outer portion of the sun has a density of less then ice. The sun only reaches the density of water at 0.5 radii. If you have a still lake a mile deep with only brownian motion, an through a rock in, it will still sink rapid. solarscience.msfc.nasa.gov/images/Dalsgaard1_density_vs_r.jpg $\endgroup$ – DavePhD May 12 '15 at 18:20
  • $\begingroup$ @RobJeffries you're right, it is mostly speculation. With all the research on core collapse supernovae, no one has really solved that problem, and this could be equally complex. The supernova process is mostly dictated by the core mass, collapsing when the core exceeds the Chandrasekhar limit. Here, the 1000 km/s initial velocity is really huge. At what point will fusion + degenernacy pressure be enough to reverse the initial kinetic energy + kinitic energy gained from gravitation collapse? What will be the products of the initial collapse, which would be on the seconds time scale? $\endgroup$ – DavePhD May 12 '15 at 18:35
  • 1
    $\begingroup$ You're right. I missed the 1000 km/s number. This is then just crazy; that is more than enough energy to unbind the Sun. $\endgroup$ – Rob Jeffries May 12 '15 at 19:23
8
$\begingroup$

If ice is "all around the sun" I fail to see how it can be moving at a velocity of 1000 m/s inwards. The mass of the sun is $2\cdot 10^{30}\mathrm{\;kg}$ and the radius $7\cdot 10^{8}\mathrm{\;m}$.

The thickness of a shell of ice with that inner radius and mass would be (assuming the usual density of ice of about 0.9x that of liquid water) approximately $10^8 \mathrm{\;m}$. That is probably sufficiently thick to withstand the gravitational attraction of the sun; certainly it will stop most solar radiation.

To take one gram of ice from absolute zero to melting takes roughly 273*4.2+334=1500 J. The sun puts out about $4\cdot 10^{26}$ W - assuming that the ice would absorb all that heat, it would take $8\cdot 10^9$ seconds to melt all the ice - a bit more than 200 years.

All that time the sun would be happily continuing to produce power - but I expect all life on earth would have ceased by the time it starts to shine again.

One obvious question - would the spherical "ice shell" be stable undertake the tremendous gravitational stress? Would it melt under the pressure? Would the pressure of the steam generated blow the water / ice outwards? It would be interesting to analyze those questions further. I suspect the over all conclusion - that a 100,000 km thick layer of water will "turn out the lights on Earth" will be unaltered by these details - because that water will still be between the Earth and the Sun, regardless of the distance and the phase.

update - a few additional thoughts.

First - the crushing strength of ice is quite low: no more than about 1000 psi (7 MPa) according to this USGS report. That is obviously many orders of magnitude smaller than the pressure on the inside of the 100,000 km thick ice shell. The average distance of the shell (mid point) is $7.5\cdot 10^8 \mathrm{\;m}$ from the center of the Sun, and will therefore experience a gravitational acceleration of

$$a = \frac{GM}{R^2} = \frac{6.7\cdot 10^{-11} \cdot 2\cdot 10^{30}}{(7.5\cdot 10^8)^2} = 240 \mathrm{\;m/s^2}$$

Thus the pressure on the inner surface is roughly

$$P = \rho a t = 0.9E3 \cdot 240 \cdot 1E8 = 2.5 \cdot 10^{13} Pa = 22 TPa$$

An obvious question to ask: what happens to ice at that pressure? The phase diagram I could find (at this location) "only" goes up to 1 TPa, but it suggests that "really cold" ice does in fact remain solid at these pressures (unlike slightly warmer ice like we normally encounter, this would be "phase XI hexagonal" ice).

enter image description here

The next interesting question is that of steam formation. If we did drop a certain volume of ice into the sun (inside the closed ice shell), what happens to the pressure? Presumably the pressure would increase somewhat, but it really isn't relevant - because again, at the pressure you would have to generate to support the ice shell, the density of the water would have to be very high - in fact, it would no longer be a gas, but a solid (or at least with comparable density to a solid - we would be in a part of the phase diagram that is not given).

Finally, the question of the potential energy of the ice - and the impact of the release of this energy on the over all equation. For the purpose of this calculation, we can't just assume that things fall to the center of the sun - even photons that are generated at the center of the sun take a long time to diffuse to the surface, so we can assume the same is true for water. Let's assume therefore that the water simply falls to the surface. While the inside of the shell only falls 1000 km, on average the ice would fall 50,000 km. The force of gravity can be considered (to first order) constant over this distance, so the work done on 1 kg of ice would be

$$W = F\cdot d = 240 N \cdot 5\cdot 10^{7} m = 12 GJ$$

The ice that fell from the inside of the shell (the first ice that melts) has less energy, namely

$$W = 240 N \cdot 10^6 m = 240 MJ$$

and I am for now ignoring the claim that the ice is moving at 1000 km/s (from the original question) as that would mean 1 kg of ice had a kinetic energy of $\frac12 m v^2 = 500 GJ$.

Whichever way you look at it, that is a very considerable amount of energy. It suggests that as the ice starts melting from the inside of the shell out, the water slamming into the surface of the sun will actually heat the sun up, speeding up the melting of the rest of the ice. The whole process will therefore take much less time than I initially estimated - there will be a runaway reaction.

Just to calibrate us - all that ice slamming into the sun adds about 12 GJ/kg * 2E30 kg = 2.4E40 J to the sun. If none of that energy was transferred to the sun, it would lead to a temperature rise of the water of about 3 million degrees. Just from the potential energy (not the initial kinetic energy). That is much hotter than the sun - so there would be a runaway melt reaction.

So it seems that after a brief time when the sun is dark (much less than 200 years), it would shine very, very brightly? Still seems like an uncomfortable solar system.

UPDATE 2

One more thought. If the ice was a little bit less dense, so that structurally it can all fall to the surface of the sun, the 100,000 km thick layer of ice would (at an initial velocity of 1000 km/s) take just 100 seconds to fall into the sun. On average, each bit of ice would fall just 1000 km, and most of the energy dissipated would be the inital kinetic energy (500 GJ/kg - much more than the 240 MJ/kg gravitational energy).

This would briefly heat the surface of the sun to a temperature of more than 100 million degrees - hotter than the core of the sun. So in that case the sun might blink briefly (while the ice is still acting as a shield) - but very quickly, it would all be over for the earth. Of course at that temperature all kinds of fusion reactions would take place - and an immense amount of heat would radiate from the surface of the sun.

It reminds me of Tom Lehrer's song - "We will all go together when we go"

There will be no more misery
when the world is our rotisserie
yes we will all fry together when we fry.

$\endgroup$
  • $\begingroup$ Some small lifeforms around deep-sea thermal vents might survive? Small consolation though. $\endgroup$ – RedGrittyBrick May 12 '15 at 13:50
  • 1
    $\begingroup$ @RedGrittyBrick I am putting my bet on the fact that this ice layer will not suddenly appear, rather than buying stock in small sea creatures... $\endgroup$ – Floris May 12 '15 at 13:53
  • $\begingroup$ Gravity inside a spherical body is exerted only by the inner part, so the shell will fall onto the Sun while it's melting. Nice answer, surely preciser than mine! $\endgroup$ – GRB May 12 '15 at 13:54
  • 1
    $\begingroup$ The question is/was 1000 km / s which makes things rather different... $\endgroup$ – Rob Jeffries May 12 '15 at 19:25
  • 1
    $\begingroup$ @DavePhD - I don't think there is enough energy to turn the sun into a supernova with "just" that much ice...we're still a couple of orders of magnitude off on the temperature. 1000 km/h = 0.003 c. $\endgroup$ – Floris May 12 '15 at 21:41
6
$\begingroup$

You can't have a "ball of ice with the mass of sun", because the ice in the middle of the ball wouldn't be strong enough to support the weight of the ice on top of it. Instead, the ice would collapse under its own gravity.

This would cause the pressure and temperature inside the ball to increase until the water molecules that make up the ice would break up into a plasma of free oxygen and hydrogen atoms (possibly a bit after the ice first melted and then evaporated, although, honestly, I'm not sure if anyone knows how water behaves at such extreme pressures), and the hydrogen would start to fuse (presumably, given the abundant oxygen, via the CNO cycle). This would increase the temperature and pressure at the core even further, and the increased pressure from the fusion reaction would finally stop the gravitational collapse.

Basically, if you had a ball of ice with the mass of sun, it would very quickly turn into a sun. A rather odd sun, to be sure (at least if you're an astrophysicist), because of the absurdly high oxygen content, but a sun nonetheless.

Of course, the fact that your ball of ice has turned into a ball of glowing plasma doesn't stop you from dropping it into the sun. What you get, if you do that, is basically a stellar collision. Unfortunately, we still don't know much about the details of what happens in such collisions, because they're fairly rare and brief events, but one likely outcome is that the stars will merge and form a single, bigger and hotter star. With lots of oxygen from the ice.

$\endgroup$
  • $\begingroup$ I understand the unrealistic parts of the question, but lets ignore that part, we can assume that the ice is not like a ball, but like a strings moving toward the sun. the key moment i want to unerstand is that how thatnear absolute zero temperature water can change the star like a sun. I can not get the point in the article wher is written that it will make the sun hotter. Anyway thanks for unswer $\endgroup$ – Aram Tadevosyan May 13 '15 at 5:38
  • 1
    $\begingroup$ @Aram you have confounded the possibility of sensible, non-speculative answers by assuming that the ice has a kinetic energy that exceeds the gravitational binding energy of the Sun. The temperature of the ice is irrelevant. $\endgroup$ – Rob Jeffries May 13 '15 at 6:51
4
$\begingroup$

Short term, the ice would be vapourised as it fell. It would mix with the sun and form a bizarrely metal-rich star of twice the mass. Such a star would have a much more opaque envelope. This leads to (once an equilibrium is reached) the final star being much less luminous and cooler than a 2 solar mass star of more normal composition.

It would probably be cooler and less luminous than the Sun (and therefore much longer lived), but by just how much is difficult to say without a detailed stellar evolution calculation. The qualitative result is correct, but extrapolation of the usual formulae for main sequence stars to these bizarre metallicities cannot be quantitatively accurate.

An interesting complication could be gravitational settling and separation of oxygen and the lighter elements. I think there are various sources of turbulence (e.g. thermohaline mixing) that would prevent this, but I doubt this has been tested theoretically in a star with such crazy abundances.

Edit: The above would be true for a collision in freefall. I missed the point about 1000 km/s, which completely dominates the energetics of the whole scenario. This is enough energy to completely unbind the Sun (by an order of magnitude), so it is difficult to provide any non speculative answer.

$\endgroup$
3
$\begingroup$

The first thing you'll notice is that the Sun stops shining. It still produces heat and light, but everything is stopped by the thick layer of cold ice.

The Sun however is not completely cold. The core is still active, even more than before. You doubled the mass, so the Sun has a higher pressure and thus can fuse easily hydrogen atoms together. The net result is more heat produced and a shorter lifespan.

In the long run the heat will trickle to the surface and the Sun will shine again. I admit I haven't done any calculations, but I think it can take up to a few million years for the Sun to shine again.

Scientist on Earth could tell that the Sun is still active. When I said that everything is stopped, it wasn't completely accurate. Neutrinos aren't particularly affected by the new layer and they can be measured on Earth as before. Not that it can give any hope, if I guessed the time scale correctly. Almost every life form on Earth would be extinct long before the Sun starts shining again.

$\endgroup$
  • $\begingroup$ Will the temperature fall in top layers decrease pressure? And if so, will core reactions explode outer layers away ? $\endgroup$ – Aram Tadevosyan May 12 '15 at 11:29
  • $\begingroup$ No, pressure will be increased. Pressure is balanced by the thermal expansion. With less velocity in the outer layer, the particles can only fall toward the center. I'm not sure about a possible explosion. It can append if the heating is fast enough, I suppose. $\endgroup$ – GRB May 12 '15 at 11:57
  • 1
    $\begingroup$ I suspect you have underestimated the inelastic collision effects. With 1Mm/s, we would not be in the relativistic realm quite yet, but still the effects would be spectacular nevertheless. We are talking about the equivalent of 0.3% Solar mass undergoing spontaneous annihilation or approximately 200 type 1a supernovae. $\endgroup$ – Aron May 12 '15 at 15:22
  • $\begingroup$ @AramTadevosyan: crucial point, there is no temperature fall if the stuff falls in. The sun's gravity is too strong for anything cold that falls into it, to still be cold (on average) by the time it reaches and interacts with the "surface". Consider what happens to meteorites that strike the earth's surface. In fact they can still be cold in the middle, if large pieces survive, but the impact generates a lot of heat and they aren't cold on average after impact once you count all the vaporised landscape. If the shell of ice somehow doesn't fall in, it can stay cold until the Sun heats it. $\endgroup$ – Steve Jessop May 12 '15 at 17:39
  • 1
    $\begingroup$ @Aron KE of ice = 1E42 J. Energy in a type Ia supernova is about 1E44 J ? $\endgroup$ – Rob Jeffries May 12 '15 at 19:30
0
$\begingroup$

First and most important effect of having two sun sized bodies in our solar system very close to each other is that this new system will throw the planetary motion off its course, and there will be chaos(Noticeable chaos right at the moment when lets us assume the ice appeared 1000 km away from sun out of nowhere). Gravitational pull will be twice as much as it is now, Earth including all planets will start revolving in spiral instead of elliptical routes until they find "peace"(equilibrium between orbital velocity and gravitational pull) in new orbit. We might not be there to see the after effects of the collision.

But below is what i think will happen after collision: Since water is nothing but 2 parts hydrogen and 1 part oxygen, And at Hydrogen is basic fuel in fusion reaction occurring on sun. So basically sun will shine brighter as Hydrogen and Oxygen from water(Ice) will break down which result into increased amount of reactants and hence the rate of reaction(hydrogen + hydrogen -> Helium + Energy) will increase significantly.

$\endgroup$
  • 2
    $\begingroup$ Not really. Most stars are not convective, that is most of the matter inside it is almost static. The added hydrogen never reaches the core, where the fusion appends. It's the pressure that increases the reaction rate. $\endgroup$ – GRB May 12 '15 at 10:56
  • $\begingroup$ The potential energy of the matter in the sun is an order of magnitude smaller than the kinetic energy of the ice bucket that the OP is throwing at it. So instead of getting this material to settle down into the sun, most of it would heat up so much that it would evaporate into space, leaving a much smaller star behind. Since the core is extremely hot, the removal of the outer shell would lead to an enormous expansion of the core, stopping all nuclear reactions but probably leaving very little material left after the expanding plasma cloud has cooled down. $\endgroup$ – CuriousOne May 12 '15 at 11:04
  • $\begingroup$ @MFH Water breaks down into hydrogen and oxygen at around 2500 C (en.wikipedia.org/wiki/High-temperature_electrolysis) so my thought is by the time the big lump of ice reaches sun, it will no longer be ICE, instead it will be a cloud of hydrogen and oxygen. Since there will be increase in mass of sun and also there will be enormous energy as bodies of 1 solar mass each will collide at the center of our solar system, It can increase the pressure & temperature at surface for sure and hence it might be possible fusion to happen on surface of sun. $\endgroup$ – JammuPapa May 12 '15 at 11:23
  • $\begingroup$ @CuriosOne The mass of ice is 1 solar mass, and it is significantly near to the sun, The gravitational well of sun will get bigger and deeper so the oxygen and hydrogen will not be able to escape the sun and eventually it will collide with sun. $\endgroup$ – JammuPapa May 12 '15 at 11:24
  • $\begingroup$ @JammuPapa: It's not so easy. The pressure profile isn't linear and the old "boundary" of the Sun is still almost near the new surface. The core increases, but not enough to enclose the entire old Sun. $\endgroup$ – GRB May 12 '15 at 11:54

protected by Qmechanic May 12 '15 at 23:32

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.