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

CCWilson

I'm considering writing a story in which we Earthlings have a few years to prepare for a cosmological catastrophe in which our planet will lose its energy source and be adrift in space. This would mean the end of life on Earth - but not right away. We could insulate giant underground chambers and tap existing energy sources in order to perpetuate human life for a number of generations into the future. Fun and complications would ensue.

So my first problem is figuring out how to create such a disaster in a believable way. I assume that long before our sun dies, it would go through a contraction phase to become a red dwarf or something and fry us for dinner. Do we believe that some stars of the size of the sun are capable of simply becoming dimmer and finally winking out? Didn't think so.

How about a scenario in which we become aware of an approaching mass - a planet-sized rock or black hole or something that we knew would hit our solar system and might somehow knock the Earth into a more distant orbit so that we would no longer receive enough sunshine to sustain life?

I'd appreciate any suggestions from you brainiacs.

mfb

- another star, crossing the inner solar system. Its gravity could modify the orbits significantly, or even catapult some planets into the interstellar region. It is possible to predict the motion of all nearby stars at least for (at least) the next hundred thousand years, giving a large time to prepare.
- a black hole, crossing the inner solar system. Similar to above, maybe harder to see in advance.
- a direct collision of a black hole and the sun. Similar to above, but I would expect that the sun will not survive this. Might have some bad side-effects.
- sufficiently advanced technology, earth-based or alien (moving the earth is way easier than messing around with sun)
- in several billion years, sun will become a red giant, burning everything on the surface and probably swallow earth. If not, the sun gets smaller again, reducing its luminosity. If some life somehow survived this, it will face an eternity of (nearly) darkness.

As you can see, the sun is quite robust. Just one option I found (the direct collision with another object of stellar mass) really modifies the sun in a significant way before it dies.

mathman

The end of life for the sun has it becoming a red giant, which might swallow up the earth. To avoid this you need to have the earth leave the solar system ahead of time (how???).

DrStupid

An object with the mass of the sun could kick us out of the system:

http://tinyurl.com/9e2c6v7

Stop simulation to see the parameters. Than fix the sun and start simulation.

CCWilson

Thanks for your replies. A star couldn't sneak up on us, so that's out for the purposes of the story. So a black hole might be the best candidate, unless an object larger than Jupiter - perhaps a planet from another star system - is possible.

DocStupid, that's a great simulation. Out of curiosity, how did you come to construct it originally? I assume that a black hole the mass of the sun could do what your generic object does in the simulation and sling Earth out into space, as long as it didn't contact us directly.

In the story, scientists would need to become aware of the approaching black hole or whatever several years in advance, so that they would have time to construct a permanent underground city. Since I don't believe that there are any objects that we know about between our solar system and the nearest star, I don't see how the gravitational effects of an approaching black hole would become obvious to us.

One possibility is that a massive black hole is captured in orbit around the sun, so that scientists would become aware of it from its effects on the outer planets, and as the orbit of the black hole slowly spirals inward, scientists would be able to calculate its future effects on the Earth. Perhaps it would be in a big elliptical orbit and we would know at some point it would be destined to cause a slingshot effect as in DrStupid's simulation.

onomatomanic

You probably already considered and discarded this, but darkening Earth's sky is a lot easier to accomplish than switching off the Sun, and has similar effects.

In the usual scenarios (nuclear winter, volcanic winter, impact winter), the darkening occurs in the wake of some primary global catastrophe, but it shouldn't be too hard to come up with a scenario that gives you the one without the other, if that's important. For example, there were serious concerns that something rather less dramatic like a sufficiently large number of burning oil wells could have a similar effect (cf wikipedia section on "Kuwait wells in the first Gulf War"). So, make a really big fire somewhere, and it gets really cold everywhere else. And stays that way for as long as the fire burns, and then some.

Of course, the psychological factors are nevertheless quite different in the two situations. Switch off the Sun, and that's it for Earth, all that's left is holding out for as long as possible. Darken the sky, and you know it's going to get better eventually, even though you may not live to see it.

mfb

Hmm... objects with a mass comparable to Jupiter might work, too. They have to come very close to earth (which gives a lot of side-effects like extreme tides), but they are hard to detect.

Black holes could be detected by their gravitational influence, as they would move the apparent position of stars. Gaia should be able to measure the position of many stars with a precision of ~100µas. For a black hole (BH) of 1 solar mass, this corresponds to light passing the BH with a distance of ~2.5*10^10km = 150 AU. Within a year, Gaia will perform several measurements of ~1 billion stars in the full solid angle. Those stars are not distributed evenly in the sky, but I will use this assumption here. Therefore, Gaia can observe a BH if a disk with 150 AU diameter occupies 1/billion of the sky. This gives a radius of ~40 light years. With 100km/s, this corresponds to 120,000 years. Hmm...
Of course, the assumption of a uniform distribution is wrong. Most stars are within the galactic disk, and not close to the sun. But so are most black holes...

Jupiter is lighter by 3 orders of magnitude, reducing all numbers by 3 orders of magnitude. With the same method, we could detect it in a distance of ~2500 AU, giving about 100 years time to prepare. That looks good.

Earth needs a kick of ~20km/s to escape. Using a=GM/r^2, delta_v=a*delta_t, delta_t ~= r/v, v=50km/s, this corresponds to a distance of closest approach of the order of 100,000km - about twice the radius of Jupiter, and comparable to the Roche limit, meaning that earth would probably break into pieces if the object gets so close. I ignored prefactors here, the distance might be larger by a factor of ~2-3, but tidal forces would be extreme and significantly change the shape of earth - not a good place to build bunkers.


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

There is no reason why it should do this.

CCWilson

Thanks, mfb.

Let's say that a black hole with the mass of the sun is approaching our solar system. First of all, how likely is it that there are black holes traveling through space after having been expelled from another star system? If such existed, can we assume anything about its velocity? Is it possible that it would be traveling slowly enough that the gravitational attraction between it and the sun would allow the two to orbit around each other (much like binary stars do)? And if that happened, what would be the effect on Earth even before the proposed slingshot effect?

CCWilson

I had wondered about that possibility. Any idea how accurate scientists could be about the speed and pathway of a sun-sized black hole that approached our solar system? In other words, would they be able to predict not just that it would pass through our solar system, and when, but that it would pass by the Earth in such way as to slingshot it out into space?

DrStupid

I'm not sure about it. This looks like as if it works:

http://tinyurl.com/c9ezmrb

But it is more a collision than a swing by. Earth would be heavily damaged or even destroyed.

In this case the object has ten times the mass of Jupiter:

http://tinyurl.com/corrbmm

As the minimum distance exceeds the Roche limit Earth would at least survive the event.

Chronos

A solar mass black hole would be unusually small. We have not detected any to date that are much less than about 5 solar masses [an interesting question unto itself]. A brown dwarf, on the other hand, would be much more probable given they are believed to be one of the most common type of star in the galaxy. They are extremely faint, but, typically in the range of 13 to 80 times the mass of jupiter. A body this size would wreak considerable havoc on planetary orbits were it to pass through the inner solar system. Chances are good they would be less than 50 years away, and quite possibly much closer, before detected. Our first clue could well be a sudden increase in the number of comets passing through the inner solar system. It is entirely possible such an event has already occured in the history of our solar system.

mjacobsca

Scientists would know pretty early that a black hole were approaching. As suggested earlier, gravitational lensing would be significant from a measurement standpoint. I believe numerous pulsars are currently used for looking for gravitational waves (search for pulsar timing array). Space telescopes like Kepler rely on precise measurements as well. Both projects would know almost instantaneously that something was wrong, long before we could see what was approaching. *Most experts on those teams would realize fairly quickly that the stars had "moved", and there are very few beneficial reasons for such an event. A black hole would be among the first things considered.

Another effect of an approaching black hole would be a disturbance in the Oort Cloud, the vast region of space beyond Pluto, and extending as much as 3 light years from the Sun, and consisting of trillions of asteroids, comets, and dwarf planet-sized objects like Pluto. The Sun has very little gravitational influence on these objects. They are very loosely bound to the Sun, and any large passing object will throw them off their orbits, either into the solar system or out. A few cosmic impacts with outer planets would be quite interesting from a sci-fi perspective. Of course, a minor impact on earth or a big one on moon would be fun, too.*

Tidal forces would affect oceans once the black hole start exerting influence on the earth. This could happen 20 years before it got here, allowing for other interesting events.*

A black hole would be almost impossible to capture by our Sun. It would have to be going slow enough already, which is improbable. A close approach and slingshot is more likely. * Also, it would be very hard to fling the Sun out from the solar system without the earth. It would be much more likely for a close call with the earth flinging the earth out of orbit instead. Maybe Mars can go with us for *fun. :) Or perhaps the black hole could get so close to the Sun that it sucks away part of the Sun's outer layers? I don't know what effect that would have.*

Perhaps an interesting plot could be that the black hole will miss us, and everything will survive, and everyone rejoices. The black hole missed the keyhole region that it needed to hit. *But then a second black hole is discovered; a binary partner trailing a light year behind. This one will hit the keyhole precisely, and hopes are dashed.*

I look forward to reading this story!

mfb

They don't have to be expelled anywhere, all stars have a motion relative to other stars on their own.

A typical velocity is ~20km/s (while some have 200km/s+), gravity would increase this to ~50km/s close to the orbit of earth. As pessimistic values, I used ~100km/s for the approach (very high -> short warning time) and ~50km/s for the close approach (low -> large gravitational influence).

No. In a two-body system, a capture process is impossible. The object cannot be bound gravitationally, otherwise it would have been close to the sun forever.

I am quite sure that the discovery of such a BH will lead to some new telescopes to track it, and telescopes improved so much in the last decades - impossible to tell how good the estimates are in 100 years, yet in 100,000.


@Chronos: See my estimate for the gravitational bending of light for black holes, it can be scaled to objects of any mass. Current technology (Gaia, to launch in 2013) can give a warning time of the order of 100years*objectmass/(jupitermass).

CCWilson

In playing with DrStupid's excellent simulation, it's obvious that the pathway through the solar system isn't all that critical in terms of whether it gives Earth a new orbit or an escape velocity. Many combinations will do that. It IS critical as to whether our planet is destroyed or not, which is important, I guess. I did see that the mass of the black hole needs to be close to that of the sun in order to have the desired effect - much smaller and unless it got lucky it wouldn't do a lot, much bigger and we'd soon be within its event horizon.

Chronos, a brown dwarf is an interesting possibility, but would have to hit just right to disturb Earth's orbit, according to the simulation.

If a sun-sized black hole were heading right in our direction, would that make it easier to detect it, or harder?

CCWilson

Thanks, mjacobsca. The Oort cloud sounds like my best shot at detecting the black hole at approximately the right time frame, if I'm to be cosmologically accurate, which I want to be.

Chronos

Lorenzo Iorio published a paper on this scenario a couple years ago - Is it plausible to expect a close encounter of the Earth with a yet undiscovered astronomical object in the next few years? http://arxiv.org/abs/1009.1374 where he concluded such an event was highly improbable. Obviously, extrapolating this analysis out to 50-100 years significantly increase the probability. Were it traveling at about the same velocity as the sun around the galaxy [~220 km/s], but, in the opposite direction, it would travel about 0.25 AU per day. Assuming its arrival in 50 years, it would currently be around 4500 AU from earth. As a basis for comparison, the aphelion of Haleys comet is about 35 AU.

H2Bro

I am surprised that no one has mentioned hypervelocity stars, which are stars / stellar masses that can have velocities three times that of our Sun's around the galaxy. Here's yet-another awe-inspiring Hubble feat (http://www.popsci.com/technology/art...ter-our-galaxy), actually detecting one such star which had been part of a trinary orbit until one member was absorbed by the SMBH at the center of our galaxy, transferring the momentum to the other two.

So, one might consider a binary orbit where one member goes supernova and the other gets hurled off on a tangent (as this event could happen far from the center of the galaxy). Still it would take very long for this star to approach the Earth....

Isaac Asimov has a book detailing various ways the Earth might end due to cosmological occurrences. It is highly entertaining to read as it is, and could spark your imagination if not provide an outright answer. http://www.amazon.com/Choice-Catastr.../dp/0449900487