What cosmological event could snuff out the sun without destroying Earth?

[CCWilson]

Guys, I appreciate all the speculation; gets my brain wheels turning. A couple of points.

The story begins just a few years from now, so that the reader can easily imagine himself living it, and the warning is only five or seven years before a black hole passes by, initially with uncertainty as to whether it will sling us into space, so that this generation is the one facing extermination. Forget genetic engineering and traveling to a moon of Jupiter and building fusion reactors and such; not enough time.

One of the issues is going to be maintaining a livable atmosphere underground. Anybody know much about oxygen generators? I do think that geothermal power plants have a lot to recommend them as a semi-permanent source of energy and perhaps a source of water as well; can't forget about water.

You'd want a farm and ranch as part of the bunker city, for dining variety, and the choice of which plants and animals to take underground would be difficult; all others would go extinct, forever.

The economic system would probably be one of central control, at least initially, and a new currency would be established. Your old money is no good here.

The process of selecting underground residents would be wrenching. After choosing scientists and doctors and other technical people, a lottery to give everyone else some small chance? Winners to bring their families? Age restrictions? No one over 40? Would rich people build their own cities underground? Could average citizens band together and survive for a while in caverns?

 

[mfb]

Fission reactors would be probably be impossible to maintain, but radiothermal generators could be maintained with minimal skills. The trouble is that I don't know what the energy requirements would be. The energy output of RTG's have been low, but traditionally they have been intended for space use where there are weight requirements.

And I'm not even sure that it would be impossible to design a fission reactor that would be need minimal intervention. Natural managed to create one at Oklo, Gabon.

The issue is not the heat generation, but the general management with radioactive stuff and so on. RTGs might work, I would try to build them with long-living material on the surface.

That actually would be a good place to start. How much *energy* does it take to keep a human alive and how much of that comes from the sun.

That is the issue. Sun gives us free ~100-500 W/m^2, averaged over a year and depending on the position and weather conditions.
Wheat production is ~1000tons/(km^2 * year), therefore it gets 3GJ/kg of light (here I used 100W/m^2). This can be improved, of course, so maybe we can assume 1GJ/kg. Light generation is not 100% efficient, but the solar spectrum is not ideal for wheat growth, so this should cancel in some way. 1GJ is 280kWh, if you would have to pay for this wheat would be very expensive, even with current power plants.
Ok... do not use wheat for food production ;).

I do think that geothermal power plants have a lot to recommend them as a semi-permanent source of energy and perhaps a source of water as well; can't forget about water.

Fun fact: They work even better without the sun, as the surface is now a cheap and very cold reservoir. And they will continue to be possible for a few billion years.
Water: Recycling. Make your complete system water-tight, and recycle everything. The ISS already uses this.

 

[CCWilson]

I wonder how fast the temperature would drop as the Earth leaves the solar system - maybe not as fast as we'd think. All that heat stored in the core would continue to warm the planet's surface for millions of years and therefore also the atmosphere, with greenhouse gases holding the heat in. So cold as hell, but probably not cold enough to freeze oxygen and nitrogen for a long, long time. A lot would depend on whether carbon dioxide and methane and other greenhouse gases would stick around. How long, I wonder, could people walk around without space suits, wearing the kind of clothing climbers of Everest use?

 

[Ryan_m_b]

This wiki page might help, especially the information regarding the head content of the Earth and the fact that the majority of heat comes from radioactive material.

 

[onomatomanic]

I did some back-of-the-envelope seasonal temperature modelling recently, which I think should work for this case.

• If I simply switch off the Sun and neglect internal heat completely, the (global average) temperature drops below 200K after about 10 weeks and below 100K after about 30 weeks.
  
  
• If I make it slightly more realistic by sending Earth directly away from the Sun with the same speed at which it orbits now, the temperature drops below 200K after about 20 weeks and is still a little above 100K by the end of the first year.
  
  
• I have a dim recollection that the equilibrium temperature of Earth due to internal heat alone would be about a tenth of its present value, i.e. around 30K. If someone could confirm or correct that value, I can incorporate that into the model.

According to the wikipedia pages, the melting and boiling points of both nitrogen and oxygen lie between 50K and 100K, for preliminary reference.

 

[CCWilson]

What do we know about frozen oxygen and nitrogen?

In a novel I've started, the Earth has been flung out of solar orbit and is chilling down. Eventually it gets cold enough to freeze the component gases of our atmosphere. Anyone know what frozen oxygen and frozen nitrogen are like? Would they be more snow-like or ice-like? Among the significant components of the atmosphere, water vapor would obviously freeze first, then carbon dioxide, then argon, oxygen, and nitrogen. I'm trying to find out what the surface of the Earth would be like at the point that all the atmospheric gases froze. Would there be a layering of the frozen gases, or intermixing? Any idea what the texture of the icy covering would be - slushy, rock hard, snowy? And I'd appreciate any help in figuring out how deep that mess would be worldwide.

 

[JohnRC]

If the Earth were flung out of orbit, it would cool down very slowly -- the core of the Earth is still hot, and a few thousand kilometres of rock is a good insulation shield. There would also be quite a lot of heat generated by the Earth's remaining reserves of uranium, potassium-40, and thorium. The oceans are also a large heat reservoir; the atmosphere is not!

The first stage, I suspect, would be a substantial glaciation, in which a normal ice-age type climate would be followed by a freezing over of all the oceans, which would progress downward to the ocean floor. All plant life would die. I would expect this part of the process to take somewhere between a month or two and a decade or two, but that is just a wild guess on my part.

There would then be a significant "pause", because nothing much else would happen between T(surface average) ~ -10°C and T(surface average) ~ -150°C. Carbon dioxide would fall as hoar frost during this period, forming a layer about 1 or 2 centimetre thick; would pack down to an ice about 4 or 5 millimetre thick.

When the surface average temperature falls below ~150°C condensation from the air will start to produce liquid argon, oxygen, and nitrogen. At this stage the ground will be warmer than the air (radioactive decay energy still reaching the surface), so that the condensation will start in the atmosphere as a fine mist, and that mist will drift to the surface as the atmosphere becomes much thinner, eventually forming oceans of liquid air on top of the frozen water oceans. These oceans would contain a fairly uniform mixture of 78% nitrogen, 21% oxygen, and 1% argon, and would average roughly 30 metre deep.
The oceans would form when the temperature reached about -190°C, and would initially be rich in oxygen and argon.

The ocean would be a pale duck-egg blue colour -- if there were any light to see it with.

Only when the temperature fell below about 210°C would solid start to form at the carbon dioxide/water ice floor of the liquid air ocean -- probably starting with large crystals of argon, followed with smaller crystals of nitrogen, and eventually by tiny crystallites of a mixture of oxygen and nitrogen (separate very small crystals in a eutectic mixture). The whole effect would be ice-like with a blue surface layer.

However, there is a steady state of surface temperature that would be achieved when the energy flow from radioactive decay from the Earth's interior matched the rate of energy loss from the Earth's surface arising from blackbody-type low frequency radiation (as a radiating body at this stage, the Earth would be far from black). With a little bit of research (which I am not prepared to do) it should be possible to calculate (or at least estimate) what this temperature might be. I do not know, but I would hazard another wild guess that this would be around about -200°C, so that the oceans of liquid water might or might not form, and probably would not freeze.

 

[chill_factor]

the atmosphere can form a convective adiabat and have an upper atmospheric temperature in thermal equilibrium with space while trapping internal heat. The amount of radiated energy would be absolutely tiny because radiation scales to temperature to the 4th power and due to convection the top of the atmosphere is the only thing that's going to be in thermal equilibrium, which is at a low temperature of something like 30 degrees - and the only way to get heat off Earth is through radiation. if the atmosphere is sufficiently opaque to far IR (which it is) then the absolute only way to radiate is by convecting warm air to the top of the atmosphere where it radiates; everything below the top layer is not going to radiate effectively because the far IR is going to be absorbed again.

Meanwhile there'll still be tidal stresses from the moon, internal heat and human heat.

Its very likely that a liquid ocean could survive and there'd only be massive glaciation instead of total freeze over.

Here's an article:

http://arxiv.org/abs/1102.1108

 

[JohnRC]

Here is the basis for some estimates:

Mass of atmosphere: 5.2 E 18 kg
density of liq nitrogen: 808 kg/m³ at boiling point -196°C
density of liq oxygen: 1142 kg/m³ at boiling point -183°C
estimated density of liquid air: 900 kg/m³ at boiling point
volume of liquefied atmosphere: 5.8 E 15 m³ = 5.8 E9 m.km²
surface area of Earth's (water) oceans: 3.6 E 8 km²

therefore average depth of liquefied atmosphere overlying present oceanic area: 16 metre

fraction by volume of carbon dioxide 390 ppm

mass of CO2 in atmosphere 390 * 44/29 * 5.2 E 12 = 3.05 E 15 kg
total surface area of Earth = 5.1 E 8 km² = 5.1 E 14 m³
density of solid CO2: 1560 kg/m³ at sublimation point –78°C
volume of solid CO2 frozen from atmosphere 2.9 E 12 m³
thickness of compact CO2 ice is therefore 0.0057 m or 5-6 mm.

----
reply to chill's post above:

Your scenario is the warmest possibility, chill. The problem with it is that the present structure of the atmosphere would not survive separation from the sun -- specifically the stratosphere which is warmed by the absorption of sunlight by ozone.

The top of the atmosphere is the thermosphere which is very very hot indeed! I presume that by "the top" you were meaning the mesopause at around 85 km altitude, which is the coldest part of the atmosphere.

If the sun were no longer in the act, then solar radiation which heats the stratosphere and the thermosphere is no longer in the action, and ozone will fairly rapidly disappear in a continuing cycle of atmospheric chemistry. There will also -- after a while -- be no cloud cover. Tidal stresses from the moon will continue to warm the Earth's from below, but they are a relatively small factor compared with continuing radioactive decay are they not?

Presumably the thermal structure of the Earth's atmosphere would revert to a simple one with decreasing temperature at increasing altitude, and you might be right that that would make radiative heat loss a very small factor; I had expected larger, with a steady state temperature around -200 °C.

Neither oxygen nor nitrogen nor argon gases can absorb infrared radiation. Once water vapour and carbon dioxide have snowed out, and methane and ozone have escaped their respective biological and photochemical replacement, and played out their chemical degradation, those are effectively the only gases left in the atmosphere -- the only reason the atmosphere is opaque to far infrared is ozone, methane, water, and carbon dioxide, as can be seen in any satellite observation through the Earth's atmosphere in the far infrared.

The Earth's low temperature darkness atmosphere would be quite transparent to far infrared.

 

[chill_factor]

yep that's true I hadn't thought of the carbon dioxide and water separating from the atmosphere.

would it be possible to pump huge amounts of methane into the atmosphere in amounts great enough to slow down the cooling?

 

[JohnRC]

yep that's true I hadn't thought of the carbon dioxide and water separating from the atmosphere.

would it be possible to pump huge amounts of methane into the atmosphere in amounts great enough to slow down the cooling?

I have checked up on the geothermal energy flux through the surface, and at present it amounts to about 0.1 watt per square metre. For that particular energy flux, the steady state emission temperature would probably be in the range of about 50-60 K if the emissivity of an ice-covered Earth were in the range 10-25%. The flux would increase with the geothermal gradient if the Earth's surface were to cool, but probably not by very much.

The steady state emission temperature is a firm number for a particular level of emissivity. Any remaining uncertainty and discrepancy between the picture that I have set out and that of chill_factor is down to the altitude and the "blackness" of the surface or atmospheric layer that the emission is effectively coming from.

There are two reasons, though, why pumping large amounts of methane might be unnecessary. The first is that the Earth is a huge thermal reservoir that would probably cool very slowly to reach this steady state. It should be possible to calculate how slowly; I have not yet done that. The second is that all of the plants are going to die in the darkness. They and the remaining microbiota will continue for awhile to metabolize and produce carbon dioxide, (and methane in some cases), until their environment gets too cool for them to continue. (Likewise the animals, but they are a much smaller part of the equation than plants and microbiota, which are roughly equal). This will prolong the period of high atmospheric carbon dioxide, and high level atmospheric emission from a layer much cooler than the surface.

 

[Borek]

Tidal stresses from the moon will continue to warm the Earth's from below, but they are a relatively small factor compared with continuing radioactive decay are they not?

I believe Andre (another user) posted links to papers that claimed radioactive decay plays much smaller role than it is commonly believed, and tidal heating is much more important. But I don't remember details and I can't find the thread where he posted it, so I can't check if I remember correctly.

 

[CCWilson]

Those answers are fantastic. Thanks.

Most discussions of why the Earth's core is so hot don't even mention tidal effects. They tell us that the three main causes are residual heat from the formation of the planet, frictional heat as iron and other dense materials sink, and radioactive decay.

What would happen if it did get cold enough to start raining oxygen all over the Earth? In particular, what if it rained oxygen over land that was cold enough to keep it liquid? Would it flow downhill? I'm trying to understand what the land surface would be like under those conditions. What would it be like to stand out there, warmly dressed, when oxygen and nitrogen rain starts to fall?

 

[Drakkith]

What would happen if it did get cold enough to start raining oxygen all over the Earth? In particular, what if it rained oxygen over land that was cold enough to keep it liquid? Would it flow downhill? I'm trying to understand what the land surface would be like under those conditions. What would it be like to stand out there, warmly dressed, when oxygen and nitrogen rain starts to fall?

Other than it flowing downhill like any normal fluid, I'm not sure what would happen honestly. Normal rainfall comes from clouds high in the sky. I'd expect that if you were standing outside as the oxygen started to liquify if would be similar to standing outside as mist formed around you. But I really don't know.

If that's true, it would be interesting for your characters to be standing outside and wiping this liquid off of them when they suddenly realize it's the oxygen in the atmosphere condensing.

 

[CCWilson]

Once water vapor and carbon dioxide and some others rain or snow, leaving mainly oxygen and nitrogen, would there be clouds? Would there be fierce wind storms, do you think? Would all the oxygen - and later nitrogen - leave the atmosphere as rain and mist, or might it snow as well? In the first case, I suspect it would mostly collect in oceans and lakes and depressions, and only freeze when the temperature dropped even lower, leaving most land areas with just a thin layer of frozen oxygen and, later, nitrogen. If it snowed oxygen and nitrogen, there might be snow drifts and maybe deep ice over land and sea.

 

[russ_watters]

That's a rough question:

Once water vapor and carbon dioxide and some others rain or snow, leaving mainly oxygen and nitrogen, would there be clouds?

That's odd because the water vapor in the air is always replenished by evaporation from the surface. We have a cycle in equilibrium. And carbon dioxide does not precipitate out.

Would there be fierce wind storms, do you think?

Off the top of my head, I'd say a lack of water vapor would reduce wind because water is partly a driver of the weather cycle. I could be wrong, though -- it is a pretty out-there hypothetical.

Would all the oxygen - and later nitrogen - leave the atmosphere as rain and mist, or might it snow as well?

No. Water precipitates because it can exist as liquid or solid at our temperature and pressure.

 

[JohnRC]

Most of the weather is driven by solar energy; with no sun, there would be much less energy to drive weather systems. However, there would still be some instability in the air column because warmer, potentially less dense air is overlain by cooler, and so convection cells may well be set up.

Apart from local factors like volcanic eruptions, I think that the air circulation might be a fairly gentle trade wind type pattern, driven by geothermal warming at the surface, and by tidal effects on both land and air mass. With solid oceans there would be no oceanic circulation to interact with the atmospheric system.

When the surface temperature gets to about -150°C (and the upper atmosphere is somewhat cooler), condensation to liquid argon and liquid oxygen can begin in the upper atmosphere. This will actually have a local warming effect (release of latent heat), and any downward motion of liquid droplets will also have a (smaller?) warming effect (dissipation of gravitational kinetic energy).

So the actual cooling is likely to stall between -150° and -200° C surface temperature.
While the cooling only proceeds slowly, oceans of oxygen will start to form -- more likely from gently descending mists rather than actual rainfall. At this stage oxygen snow is unlikely, because oxygen has a good wide liquid range. Towards the end of this stage, though nitrogen will probably form as crystallites of snow or hoar frost as well as mist. And the other factor is that the atmosphere will become very thin.

At about -210°C = 63 K the oceans -- uniform depth of about 14 metre over the oceanic 71% of Earth's surface -- will start to freeze. The atmosphere at this stage will have a pressure of roughly 4 Pa, made up of about 60% neon, 25% nitrogen and falling, 13% helium and very slowly rising, and 1% hydrogen (this does not allow for any meteoric material that might have been picked up during Earth's escape from the solar system

 

[Borek]

That's odd because the water vapor in the air is always replenished by evaporation from the surface. We have a cycle in equilibrium. And carbon dioxide does not precipitate out.

Once we get to temperatures where nitrogen and oxygen are liquid, water and carbon dioxide become rock solid (pun intended). They will be still able to sublime, but I am not convinced their partial pressures will be high enough to be of any meteorological importance.

 

[CCWilson]

When the surface temperature gets to about -150°C (and the upper atmosphere is somewhat cooler), condensation to liquid argon and liquid oxygen can begin in the upper atmosphere. This will actually have a local warming effect (release of latent heat), and any downward motion of liquid droplets will also have a (smaller?) warming effect (dissipation of gravitational kinetic energy).

Wouldn't the liquid argon and oxygen that condense out initially at high altitude return to a gaseous state as they fall to warmer temperatures, resulting in no net heat loss or gain - until low altitudes are cold enough to maintain them in a liquid state?

So the actual cooling is likely to stall between -150° and -200° C surface temperature.
While the cooling only proceeds slowly, oceans of oxygen will start to form -- more likely from gently descending mists rather than actual rainfall.

Would the oxygen liquify preferentially over the oceans, or would it follow existing streams and rivers to run downhill to oceans and lakes?

Any rough guesses as to how long it might take before oxygen and later nitrogen begin to liquify?

Thanks a lot for your help.

 

[JohnRC]

Wouldn't the liquid argon and oxygen that condense out initially at high altitude return to a gaseous state as they fall to warmer temperatures, resulting in no net heat loss or gain - until low altitudes are cold enough to maintain them in a liquid state?


Would the oxygen liquify preferentially over the oceans, or would it follow existing streams and rivers to run downhill to oceans and lakes?

Any rough guesses as to how long it might take before oxygen and later nitrogen begin to liquify?

Thanks a lot for your help.

You are quite right -- there would be an initial period when high level condensate would evaporate again at lower levels. The overall effect would be a transfer of heat upward which would reduce the temperature gradient through the atmosphere.

The other thing, though, is that we are talking about 20% of the atmosphere potentially condensing out at high levels which would result in a fairly major updraught of lower level air to "fill" the resulting void. When the major gases in the atmosphere start to condense out there will be a fairly rapid drop in atmospheric pressure. My instinct for fluid dynamics is not good enough to guess at the overall consequences during this phase. It is quite possible that after a fairly quiet cooling phase from -50 °C to -150 °C, the condensation of major atmospheric gases will introduce a stormy and turbulent phase in the atmospheric behaviour.

Similarly for the rainout. On Earth at present, water rainfall is preferentially over land because air masses are driven upward by surface topography, with resulting cooling and condensation. So if there was major air circulation, and associated stormy weather, I think that oxygen precipitation would similarly occur mainly over land. If on the other hand, the atmosphere remained fairly calm and quiet during this phase, I think there would be even precipitation over land and ocean. I cannot at present think of any mechanism that might lead to preferential precipitation over ocean.

And no, I would not care to hazard a guess as to how long. Probably not less than a year, because this phase of the cooling is fairly close to the long term steady state temperature profile, and we cannot be sure how close. So the guess I would make if forced to would be anywhere between a year and a few millennia.

 

[CCWilson]

Let me rekindle this discussion with a further question. We have the Earth slung out of its orbit by a passing black hole of 3 solar masses. By the way, this would probably - according to Dr Stupid's gravity simulator - disrupt the entire solar system, tossing planets and even the Sun hither and yon, depending on how close to the Sun it passes. Although the moon is not included in the simulator, I suspect that it would also be thrown asunder, with the possibility of even crashing into the Earth, which would introduce complications that I don't think the story needs. Another possibility is that the black star would sling us into the Sun, which would be dramatic but a novel-killer.

My question is this: Since the black hole would not pass too close to the Earth, it would probably have no more direct tidal effects than the moon does. But the slingshot effect - the Earth going in one direction, then suddenly whipped in another direction - it seems to me that an observer on Earth would feel like he was on a carnival ride and experience a lot of centrifugal/centripetal force. Agree? And it seems obvious that the change in direction would also cause massive tidal waves. Am I right about that?

 

[mjacobsca]

LONG before people would feel any sort of "carnival-ride" forces, the Earth would experience tremendous tidal effects from the 3 solar mass black hole, causing ruptures in tectonic plates and mass devastation. One could envision Yosemite's super-volcanoe and other volcanoes erupting all at once, high tides that travel miles inland, and the release of a ton of carbon dioxide into the atmosphere (hey'll, we'll need that warmth as we travel out of the solar system).

If the BH got close enough to syphon atmosphere or compete with the gravity of the Earth itself to change our gravitational field, the Earth would be in serious trouble. You might not want to have it come that close, or your story would be over before it started.

One interesting effect of a BH, for which I don't know the math, is that it would probably disrupt satellites in orbit enough to destroy world-wide communication. A cool possibility would be most of the "good countries" satellites being sent out of orbit or crashing into the Earth, but an enemy's satellites somehow survived, giving the enemy a tremendous advantage over the "good" side. Spy operations would have to return to basics for the duration of the novel.

 

[Evo]

LONG before people would feel any sort of "carnival-ride" forces, the Earth would experience tremendous tidal effects from the 3 solar mass black hole, causing ruptures in tectonic plates and mass devastation. One could envision Yosemite's super-volcanoe and other volcanoes erupting all at once, high tides that travel miles inland, and the release of a ton of carbon dioxide into the atmosphere (hey'll, we'll need that warmth as we travel out of the solar system).

If the BH got close enough to syphon atmosphere or compete with the gravity of the Earth itself to change our gravitational field, the Earth would be in serious trouble. You might not want to have it come that close, or your story would be over before it started.

One interesting effect of a BH, for which I don't know the math, is that it would probably disrupt satellites in orbit enough to destroy world-wide communication. A cool possibility would be most of the "good countries" satellites being sent out of orbit or crashing into the Earth, but an enemy's satellites somehow survived, giving the enemy a tremendous advantage over the "good" side. Spy operations would have to return to basics for the duration of the novel.

What about the lack of a sun? Might put a damper on things...just saying.

 

[CCWilson]

I'm not so sure about huge tidal and tectonic effects from the gravitational effects of the black hole. The Sun, for example, has much less tidal effect than the moon, because the distance from one side of the Earth to the other is a significant part of the distance from Earth to moon, but a very small part of the distance from Earth to Sun. So unless the black hole passed fairly close, it would affect all parts of the Earth more or less similarly. That's why I think the effect due to the Earth's change in direction would be the significant factor.

 

[Evo]

I'm not so sure about huge tidal and tectonic effects from the gravitational effects of the black hole. The Sun, for example, has much less tidal effect than the moon, because the distance from one side of the Earth to the other is a significant part of the distance from Earth to moon, but a very small part of the distance from Earth to Sun. So unless the black hole passed fairly close, it would affect all parts of the Earth more or less similarly. That's why I think the effect due to the Earth's change in direction would be the significant factor.

Are you saying that the Earth would remain in it's exisiting orbit around the sun?

 

[CCWilson]

No. The premise of the story is that the Earth is slung out of solar orbit and loses its energy source, and with around five years lead time, a number of huge underground cities are built using mostly geothermal energy to generate electricity and keep our species going.

 

[mfb]

Tidal effects scale with M/r^3, orbital influence scales with M/r^2 - if we fix the orbital influence (enough to kick Earth out of the solar system), a bigger mass reduces tidal effects. We know that our sun influences the path of Earth in a significant way (we orbit it), so a black hole with 3 solar masses in a distance of about 1 AU (and a velocity of the order of 30km/s) could kick us out, while its tidal influence is smaller than the moon's. Completely negligible compared to the influence on the orbit.

 

[CCWilson]

mfb, what about the effects of the change in direction on the Earth, both on an observer sitting in a lawn chair and on the tides? In other words, if you're jogging along holding a pail of water and a cat carrier and then make a sharp right turn, the water sloshes up on the outside of the pail, and the cat is thrown toward the side of the carrier to the outside of your turn. I also wonder whether there would be geological effects that would predispose to earthquakes. Obviously the magnitude of those effects would depend on whether the Earth was whipsawed around the black hole or simply pulled into a slightly different path.

 

[mfb]

Those are all tidal effects. If the moon does not tilt your cat, a black hole in 1 AU distance would not do that either. Similar with earthquakes.

If the black hole comes closer, it can have significant tidal effects, but they are not required to remove Earth from its orbit.

 

[CCWilson]

Beg to differ. Tidal effects occur because of the differential gravitational forces of the moon on the oceans on the near side (greater) vs the oceans on the far side (lesser). That's why the moon has more tidal effect than the sun - because the diameter of the Earth - 13,000 km - is a significant percentage of the distance from moon to Earth (400,000 km) and a very small percentage of the distance from Sun to Earth (150,000,000 km) - so the difference in gravitational attraction from near to far side is greater for the moon, even though the Sun is much more massive than the moon.

But we're not talking here about a difference in gravitational attraction between two sides of the Earth. Our planet is being slung out of its orbit not by tidal effects but by the gravitational attraction of the black hole to the Earth overall. I agree that the tidal effects wouldn't necessarily be large, but the centrifugal/centripetal force from the change in direction would. I suspect that earthquake generating effects would be small, but the water in our oceans would, I think, be sloshed around, resulting in high tides, and I'll bet a human would feel those carnival-ride effects.

 

[mfb]

Our planet is being slung out of its orbit not by tidal effects but by the gravitational attraction of the black hole to the Earth overall.

You cannot feel an homogeneous gravitational field - one of the fundamental rules in General Relativity. You can feel the different gravitational attraction at different points, and those are tidal effects. Without those tidal effects, Earth could accelerate with whatever value in any coordinates - it does not matter, as all objects get the same acceleration.

 

[CCWilson]

I may be coming around to your opinion on this - but it's a brain twister. Thinking about the Earth in relation to the solar system, if the Earth got whipped around slingshot fashion, you'd think an observer on Earth would feel the change in direction. But I shouldn't think of the Earth in relation to the solar system, but more in relation to spacetime. The black hole would massively deform spacetime, and the Earth and everything on it would simply be along for the ride, floating along where the gravitational forces tell it to go. The only gravitational effects we would feel would be those of the Earth, as usual.

I'm still not sure of this, however. Bears further contemplation, especially since the gravitational fields are changing.

 

[onomatomanic]

I'm still not sure of this, however. Bears further contemplation, especially since the gravitational fields are changing.

The key concept here is "being in free-fall". You do not feel any gravitational forces with respect to which you are simply falling. That includes the Sun and the Moon, and, for someone in orbit, the Earth as well. Analogously, it includes the Black Hole. The only reason we do feel the gravitational force of Earth is that, not being in orbit, we aren't able to fall - because the pesky surface gets in the way, sooner or later (hopefully sooner, for practical reasons).

 

[Evo]

I may be coming around to your opinion on this - but it's a brain twister. Thinking about the Earth in relation to the solar system, if the Earth got whipped around slingshot fashion, you'd think an observer on Earth would feel the change in direction. But I shouldn't think of the Earth in relation to the solar system, but more in relation to spacetime. The black hole would massively deform spacetime, and the Earth and everything on it would simply be along for the ride, floating along where the gravitational forces tell it to go. The only gravitational effects we would feel would be those of the Earth, as usual.

I'm still not sure of this, however. Bears further contemplation, especially since the gravitational fields are changing.

How about the fact that life could not exist without the sun, no matter how far down you dig? How do you grow crops? How do you raise lifestock? How do you create an environment for humans? Waste disposal? Potable water? Breathable air? I assume the seas and all sea life were abandoned. Is this some silly Noah's Ark scenario?

Animals? Plants? How many humans did you plan to take underground out of all of the billions?

Medicine? Hospitals and medical care?

Even assuming some life is possible, what's the quality of life and how do you accomplish it?

 

[CCWilson]

Evo, that's what the novel is all about. I've worked out most of the issues you raise. If you're interested, scan this thread, unless its silliness puts you off your feed.

 

[mfb]

How about the fact that life could not exist without the sun, no matter how far down you dig?

What about 3km to find Desulforudis audaxviator?
Well, and an artificial environment might work as well.

 

[sadben]

I think that an extra solar object of sufficient mass is the best bet: Aliens are a silly way of implementing "Deus ex machina"

 

[JohnRC]

If you can afford to have a lead-in time of about 7-10 years while the Earth was slowly being ejected from the solar system, then the scenario that would least affect humanity would be a fly-by of some sort (from an object within or outside the solar system) that gently accelerated Earth into a rather more eccentric orbit, leading to gravitational whip effect ejecting it from the solar system when its path took it close to Jupiter on the first orbital pass-by.

This scenario would have the additional advantage that you would be free to do whatever you wanted with the moon -- destroy it, remove it, or leave it.

 

[FalseVaccum89]

Not without technology. There are no objects of sufficient mass to capture the black hole.

Actually, this is not accurate; unless one is near the event horizon of a black hole, one experiences the exact same level of spacetime curvature (thus the same level of gravitaitonal force) as with a normal body of comparable mass. A black hole should have the *exact* same effect as a star with comparable mass, unless it were to collide with something.

 

[Drakkith]

Actually, this is not accurate; unless one is near the event horizon of a black hole, one experiences the exact same level of spacetime curvature (thus the same level of gravitaitonal force) as with a normal body of comparable mass. A black hole should have the *exact* same effect as a star with comparable mass, unless it were to collide with something.

He's talking about our Sun capturing the black holes in an orbit. Since the Sun is much less massive than any known black hole, such a thing is not possible.

 

[onomatomanic]

^ Exactly. And the post mfb's was in reply to specified that this is a "massive black hole", so we don't even have to rely on its conforming to the known/predicted mass range. No capture is possible between the two stellar-mass objects without the assistance of at least one other in that range.

 

[mfb]

Thanks Drakkith and onomatomanic.

To quantify the ability of our solar system to catch massive objects:
Assume that a massive, slow-moving object (10km/s far away) approaches our solar system. Assume that its mass is small compared to the mass of sun (the reason will become clear later). How can we capture it? Gravitational interaction with a planet. It has to dump enough energy to fall below escape velocity - and it has to do so in a single interaction, as two significant interactions with planets in a single pass through the solar system are extremely unlikely.
The best geometry is a head-on approach to a massive, fast-moving planet, with a very near miss: With the approximation that all objects are point-masses, the planet will be shot in the opposite direction, getting a velocity kick of twice the relative velocity. Real planets have a finite size, which can limit the maximal momentum transfer to lower values, but I will neglect this issue here.


We need massive, fast-moving planets close to the sun... I will begin with Jupiter here and consider Mercury afterwards:

Jupiter orbital velocity 13km/s
Escape velocity (solar system) at its distance: sqrt(2)*13km/s = 18.38km/s
Velocity of incoming object at Jupiter orbit: sqrt(10^2+18.38^2) km/s = 20.93km/s

Relative velocity: 20.92km/s+13km/s = 33.92km/s.
=> Jupiter velocity change 2*33.92km/s = 67.85km/s
Required velocity change of incoming object: (20.93-18.38)km/s=2.54km/s.

=> maximal mass of incoming object: 67.85/2.54 = 26.7 Jupiter masses = 0.026 solar masses.

Mercury: Orbital velocity 47.87km/s, maximal mass of incoming object 317 mercury masses = 0.055 Jupiter masses.

As you can see, Jupiter's mass dominates the results - even with Earth in a mercury orbit, 317 Earth masses would be about one Jupiter mass (and not 26.7).


This gives 26.7 Jupiter masses = 0.026 solar masses as an upper limit for any reasonable capturing process in the solar system.


What happens if we take the finite size of the objects into account? Objects with 26.7 Jupiter masses are brown dwarfs, with a size similar to Jupiter.
Escape velocity scales with sqrt(M/r), at twice the Jupiter radius (closest possible flyby without touching) this corresponds to 60km/s*sqrt(26.7/2)=220km/s. Based on an initial relative velocity of 33.92km/s, the velocity at closest approach is sqrt(220^2+33.92^2)km/s=222.6km/s.

Calculate the (minimal) eccentricity:
$e=\sqrt{1+\frac{2\epsilon h^2}{\mu^2}}$ with ε=1/2 (33.92km/s)^2, h=4*(jupiter radius)*(222.6km/s) and μ=G*26.7*(jupiter mass)
=> e=1.175
This gives a maximal deflection of 2.04 or 117° - in other words, only ~85% of the maximal velocity change can be used and the maximal mass is even lower. And a minimal separation of 2 Jupiter radii is not possible anyway - the brown dwarf is extremely dense, its Roche limit for Jupiter will be significantly larger.

I would expect ~15 Jupiter masses as a more reasonable number.

 

[CCWilson]

How about a relatively slow moving black hole of the mass of the sun? Could that be captured into a binary?

 

[Drakkith]

How about a relatively slow moving black hole of the mass of the sun? Could that be captured into a binary?

Doesn't matter. The Sun, and most everything else in the solar system, would fall towards a black hole, as it falls towards the Sun, with both the Sun and the BH gaining velocity the whole way and being flung out after closest approach. Once away from each other their relative velocity would be similar to what it was before the encounter. Stellar mass black holes are also not the mass of the Sun, but on the order of around 3+ solar masses. There is no known way for a black hole to form with just 1 solar mass.

 

[Ryan_m_b]

There is no known way for a black hole to form with just 1 solar mass.

At first I wondered about a larger black hole shrinking over time to one this size but the universe isn't old enough by far to allow for that type of time scale.

To the OP how about a very small black hole falling into the sun? Over time the sun will shrink and dim as it falls in (though I'm not sure how the exact process will go). As it's sci fi you don't have to explain exactly how this small black hole was formed, you could even mention it baffled scientists but they've got bigger things to deal with now.

 

[mfb]

If we allow very improbable events, there are two small loopholes:

- let a brown/red dwarf scratch the surface of sun, capturing ~2*10^(-4) brown/red dwarf masses, and let it get very close to a planet afterwards (probably Jupiter) to give it some angular momentum. It will end in an extremely eccentric orbit, but bound in the solar system. This needs additional perturbations to get some stable system afterwards, but at least it is possible.
The same would be possible with a black hole of << 1 solar mass, but unless there are primordial black holes with that mass they do not exist.

- the sun could probably perform a similar capturing mechanism around a black hole, swallowing a planet afterwards to get some angular momentum. This event would ruin the whole solar system, some planets would fly away and the others would get completely new orbits afterwards.

 

[CCWilson]

Doesn't matter. The Sun, and most everything else in the solar system, would fall towards a black hole, as it falls towards the Sun, with both the Sun and the BH gaining velocity the whole way and being flung out after closest approach. Once away from each other their relative velocity would be similar to what it was before the encounter. Stellar mass black holes are also not the mass of the Sun, but on the order of around 3+ solar masses. There is no known way for a black hole to form with just 1 solar mass.

I understand that a black hole formed by the collapse of a massive star would be at least 2 1/2 solar masses in size - and that's the size of the black hole in my story. However, don't some physicists believe that some black holes may have formed near the big bang by some mechanisms that we don't fully understand that could indeed give us smaller black holes currently?

 

[Drakkith]

I understand that a black hole formed by the collapse of a massive star would be at least 2 1/2 solar masses in size - and that's the size of the black hole in my story. However, don't some physicists believe that some black holes may have formed near the big bang by some mechanisms that we don't fully understand that could indeed give us smaller black holes currently?

I've never heard of that, but I'm not an astrophysicist or cosmologist, so I really can't say for certain.

 

[mfb]

Could exist, but remains unconfirmed. It would be quite surprising if the first detection happens within our solar system ;).