How do you non-catastrophically reduce the mass of the Sun by half?

Question

In my previous question, I asked how much mass the Sun would have to lose in order for Saturn's orbital velocity to be its escape velocity.

The answer proved to be somewhat unexpected - when the Sun loses about half of its mass, every planet will escape from the Sun's remaining gravity at about the same time.

So this is the promised follow-up question:

What plausible, believably feasible (not necessarily absolutely physically valid) method could be posited as a way for the Sun to lose 50% of its mass, without going through some catastrophic process?

Criteria and limitations:

A. Must occur within a millennium or two.

B. Should not involve intervention of some 'superior alien intelligence', but must be derived from some plausible natural event. (Somewhat lenient on this, but any alien intervention must be completely independent of the Solar System and not require any presence in the Solar System. That is, extraneous 'spooky action at a distance')

C. Must not create any phenomena that would have devastating consequences on life on the planets (i.e.: no radiation, excessive heat, energy surges) except for the diminishing of the Sun's current Solar contributions. The Sun just reduces in size, energy, and mass, but otherwise functions normally.

D. Once the planets are clear of the system, what happens to the sun thereafter is irrelevant.

E. The removed mass of the Sun must be done in such a way that the removed mass no longer contributes to the gravitational effects of the Sun.

F. The current position of the sun as the center of the Solar System can not be altered (Newton's Laws must be enforced).

G. The ejected mass can not itself become an alternative gravitational center sufficient to influence the planets, but must be dispersed into the galactic void. However, it is allowable for it to collect again and form a significant gravitational source somewhere else. The ejected mass does not necessarily need to reach escape velocity, but by some effect widely dispersed or otherwise relocated.

H. It is allowable that, if the mass depletion occurs over time, the planetary orbits can correspondingly move away from the Sun until they reach escape velocity, with all attendant effects of doing so permitted.

Assume that the life on the planet is not dependent on energy from the Sun, but on independent locally sourced forms of energy. That is, life on the planet can be supported absent the Sun (No need for Solar light, heat, energy, gravity, or other Solar contributions). With that in mind, if any of these criteria are modified, then the modification must not effect the viability of life on or physical integrity of the planets, in any way.

The method does not necessarily have to be under the control of any intelligent intervention, preferably not from any intervention from within the Solar System. Note, this is not a criteria.

Note this does NOT have a hard science tag. The effect can be caused by some as-yet-unknown but plausible scientific concept.

EDIT

The Solar System does not absolutely have to be our solar system, but my planet-moon combo is based on Saturn or Jupiter. Humans are not a factor, and thus their intelligence and fate is inconsequential.

Another EDIT

Please also recall that, as the Sun loses mass, its gravity decreases and further mass loss will take less energy. That is, the remaining mass is not as tightly held as the starting mass. This fact may or may not be useful in your answer.

Clarification EDIT

Some may be thrown off by criteria C. The restriction on life is clarified by the later assumption stated after H. As long as the planets remain physically intact and maintain their integrity and general composition, criteria C is met. The planets have the same general structure, chemistry, and geological features.

Answer 1

C. Must not create any phenomena that would have devastating consequences on life on the planets (i.e.: no radiation, excessive heat, energy surges) except for the diminishing of the Sun's current Solar contributions. The Sun just reduces in size, energy, and mass, but otherwise functions normally.

That is not possible, for three reasons.

1. About a third of the tidal influence on the Earth comes from the sun. Even if Earth would not escape, the tides would be changed globally, too fast to be nice on coastal ecossystems worldwide, which would all be f... Rough-loved. Other neighbouring ecossystems could follow in collapse.

2. The sun protects planets from interstellar radiation with its solar wind. The fact that Earth's rotation axis is kinda orthogonal to its orbit helps us survive solar flares, which always hit us perpendicularly. Once exposed to interstellar wind, we will all be f.. fried by crazy amounts of radiation coming towards the poles. We don't need to escape the sun for that to happen - merely moving the heliopause in can terminate us.

3. If a rocky planet surface does not depend on the sun to achieve a life-sustaining temperature, then either it is going through a hadean phase or it is excessively radioactive - neither situation would allow for complex life, maybe not even any life at all.

Answer 2

Wormhole

[A,C,D,E,F,G] A traversalable wormhole would be an excellent mechanism to remove mass from the sun. A wormhole is consistent with general relativity while avoiding all of the pitfalls of violently moving mass from the center of the solar system (which could cause all kinds of orbital perturbations that would be chaotic or even fatal).

[B] Would you consider human construction natural? Perhaps humans build a wormhole. For convenience and efficiency they place it in the inner solar system (perhaps it requires a significant and constant stream of particles to remain stable so it's placed right next to the sun). Either by miscalculation or accident it falls into the sun. Unable to retrieve or destroy the wormhole it is left to silently eat away at the mass of the sun.

Answer 3

There are a number of ways a star can lose mass, and I think it's worth talking about them:

• A normal coronal mass ejection may contain $\sim10^{-18}M_{\odot}$, which is also extremely low. Eta Carinae's Great Eruption averaged about $1M_{\odot}\text{ yr}^{-1}$, but this is not an expected event in Sun-like stars.
• Superflares are possible in Sun-like stars, although only in a very small population (1%), and likely would not remove as much mass.
• The solar wind blows away mass at a rate of $\sim10^{-14}M_{\odot}\text{ yr}^{-1}$. Even the hottest O stars lose mass at $\sim10^{-5}$ or $10^{-7}M_{\odot}\text{ yr}^{-1}$ at the most. When the Sun becomes an AGB star near the very end of its life, it may lose mass at a rate of $\sim10^{-4}M_{\odot}\text{ yr}^{-1}$, and so an extended AGB phase is a possibility, maybe involving a late thermal pulse leading back to the asymptotic giant branch.
• I do like LarsH's suggestion of bipolar jets. They've been observed in T Tauri stars, pre-main sequence stars that often evolve to become Sun-like. In other words, the Sun may have developed jets within the first ten million years or so of its life. However, I suppose it's really not going to happen anytime soon; T Tauri stars are very active, and have strong stellar winds that aid outbursts.

I think superflares are your best choice if you want the event to occur at the present stage of the star's life. If you are willing to have the star be very young, pick a T Tauri wind and bipolar jets, dramatically enhanced by some unknown factor. If you are willing to have the star be older and more evolved, a strong AGB wind might work.

Let's look at the timescales $\tau_{1/2}$ we'll need for the various processes, in order to lose $0.5M_{\odot}$: $$ \begin{array}{|c|c|c|c|}\hline \text{Process} & \text{Evolutionary stage} & \dot{M}\text{ }(M_{\odot}\text{ yr}^{-1}) & \tau_{1/2}\text{ }(\text{years})\\\hline \text{T Tauri wind}^1 & \text{Pre-main sequence} & 10^{-7} & 5\times10^6\\\hline \text{Superflares}^2 & \text{Main sequence} & 10^{-11} & 5\times10^{10}\\\hline \text{G star wind} & \text{Main sequence} & 10^{-14} & 5\times10^{13}\\\hline \text{O star wind}^3 & \text{Main sequence} & 10^{-5} & 5\times10^4\\\hline \text{AGB wind}^4 & \text{Asymptotic giant branch} & 10^{-4} & 5\times10^{3}\\\hline \end{array} $$ _{¹Lecture notes, Ohio State University
²Osten (2015)
³Cohen et al. (2011)
⁴Lecture notes, University of Bonn}

Your best bet, overall, would be a system with an AGB star rapidly losing mass. Note that I give the time it would take for an O star to lose $0.5M_{\odot}$, but that would only be a small fraction of its total mass - not half. You'd need to extent that timescale by a factor of about 20 for it to lose half of its initial mass.

Answer 4

The gravitational binding energy of the sun is given by

$$\frac{3 G M^2}{5R}$$

If we ignore the radius component, halving the mass of the sun would involve:

$$\frac{3 \cdot 6.674 \cdot 10^{−11}\;N \cdot kg^{–2} \cdot m^2 \cdot (10^{30}\;kg)^2}{5*695 508\;km}$$

or $5 \cdot 10^{40}\;J$.

The sun emits $3.846 \cdot 10^{26}\;W$ of power, so this is about $10^{14}\;s$ of solar output, or 4 million years give or take.

If the process was 90% efficient it would increase the sun's energy output 1000 fold, frying most of the solar system. Uranus would get 2.5 as much energy per unit area than Earth does now. Objects at 15 AU out would get as much energy from this process as Mercury does now.

No plausible natural event is going to be 90% efficient at getting matter away from the Sun. The Sun is a gravitationally-bound fusion-supported structure. It already generates huge amounts of energy to keep itself supported at its size; getting large amounts of matter out of a Sun is going to be non-trivial effort for a Type-3 civilization.

It would be a project that would, on its scale, equivalent to the energy consumed by the Manhatten Project (which used lots of energy as part of the separation process).

There is no plausible way this at all appears natural. And anyone doing it unnaturally would have to do extreme measures to prevent energy lost as waste heat from cooking the solar system.

Answer 5

I'm building up on top of Skek Tek's answer.

First, humans build a pair of wormholes using some handwavium advanced technology. Entering one exit of the wormhole lead directly to the other exit and vice-versa, it is a two-way road. Further, the wormhole is pretty much stable and undestructible and it is also big enough to allow the passage of a very large stellar fleet at once.

The purpose of the wormhole is to allow the humans to explore the galaxy easier. So they send one of the wormholes into an hyperbolic orbit out of the Solar System into a galactic orbit and keep the other near the Sun.

Some time later (possibly a few millenia), due to an accident, miscalculation, sabotage or something else, the wormhole falls into the Sun. As a result, it starts to pump matter to the other end. Since the other side is in intergalactic space and the entering matter don't exit the other end with a velocity large enough to escape, the matter at the other end forms a ball of gas bound by gravity around the wormhole.

Since the wormhole is a two-way device, stellar matter can travel in either direction. This means that its movement would be governed by pressure, gravity and temperature. Matter would flow from the Sun through the wormhole (and some matter would flow back) until both sides have the same amount of matter and an equilibrium is reached.

In the end, we would have a new star in the sky featuring half of the Sun mass and our own Sun would feature the other half of the mass. Further, it would give a really new and more precise definition to the term "Sun twin star".

Alternative scenario: If matter do exit the other side of the wormhole with enough velocity to escape, then the Sun is pretty much doomed. Except if someone or something could destroy/deactivacte/close the wormhole exactly in the mid-way of this proccess, saving the Sun, but with only half of its original mass.

Answer 6

If we limit ourselves to known physics, then we are requiring a solar-scale event to occur to this system. Nothing can cause half the mass of a previously stable star to disappear by itself; certainly the stability required for intelligent life to evolve is incompatible with the sudden demise over a millennia.

So some event involving something external to the planetary system must occur, which triggers the outflow of mass.

Pot black

Consider, then, some external body on or close to a collision path with the star. The thing arrives, interacts with the star, and continues out of the system, either triggering a mass loss or taking mass with it (or both). One candidate for this would be a black hole - any actual star-star collision would certainly eject a lot of solar material and sterilise the surface of the planets. A black hole, however, could pass near or through the star, pulling significant chunks of mass out of the star (depending on the mass of the black hole).

Note, however, that as with snooker, momentum would be transferred to the star from the black hole; this could be enough to fulfil the motivating requirement that the planets achieve escape velocity; by moving the star (and dragging the planets to a degree), the planetary dynamics would be changed. If the black hole crossed the system transverse to the current motion of the planet, it would have a strongly different effect on the planet and the star, and could conceivably destabilise the planet's orbit entirely.

This achieves several of the requirements, and if the black hole moved transverse to the plane of the planet's orbit, then the trails of solar mass resulting from the impact would largely miss the planet itself.

Canon the yellow

A very different mechanism which might be conceptually neater would be to start with a binary system (per about half the solar systems we can see), and have a body arrive which knocks one of the two stars out of the system. This would require the two stars to be a good distance apart, but for stable planetary orbits not too far apart.

If the knocked-out star was a black hole, then the planet-dwellers would not even see the sun dim; in fact without a black hole pulling matter from its sister it would perhaps brighten. But a vast proportion of the mass about which the planets were orbiting would be gone.

In this scenario I would argue that the arriving body needs to move as fast as possible; the slower it arrives, the longer it is disrupting the gravitational map of the solar system, and the more likely it is to cause some sudden catastrophe on the planet. A sudden punching arrival of a star pulling a black-hole out would instead leave little time for the existing bodies to adjust. Also the faster it impacts, the more momentum both have to leave the system.

Note that for both bodies to leave the system, the arriving body must be of much higher mass.

Europa

In all these stellar impacts, it is very difficult to construct one which does not just spew stellar material across the planets. A plausible survival story could be a planet or moon like Europa, which has a thick ice surface and likely a water layer beneath. This would protect from a significant range of gas and dust debris, and forms a stronger protection than a magnetosphere. Also, Europa is believed to be heated significantly by the tidal stresses of orbiting a gas giant, which is notable for the story; firstly, because the changing stellar radiation would not be too problematic for the continuation of life as the star dies, but also because it could continue as the gas giant slowly escapes the system to become a rogue planet.

Answer 7

The sun could (howsoever) spin faster and faster (Beyblade, beyblade let it rip), and due to centrifugal forces the sun looses mass,
It could come to massive eruptions, which were luckily not in direction of earth, or the sun simply looses mass which is going to space dust and fog and stops shining. While sun loses mass also gravitation is lowered to the point where planets moving away from the sun. Hope this helps :)

Answer 8

The star is infected with a parasitic organism which converts helium into handwavium. These solar parasites lie dormant for several billion years, slowly accumulating energy in a small pocket universe, until a threshold is reached.

Once that threshold is achieved, the organism begins to convert hydrogen into erewhonium, a form of energy which can travel faster than light. It then manipulates its pocket universe in such a way that it intersects with a similar pocket universe in another star.

For unknown reasons (aesthetics? convenience?) the creatures always extend their pocket universe channels outward in the direction of the star's poles. Since the beam is highly directional, there's no direct effect on the planets, and while most of the energy is traveling through an alternate universe, there would be some spillover, causing columns unusual radiation and visible light to appear at the poles of the star, slowly extending outward. The initial appearance of these columns is the first warning sign that the star will be shrinking.

Answer 9

Have you considered a very dilute plume of antimatter falling into the star over a long period of time? It'd increase the energy output of the star, possibly making it even harder to detect by anyone watching. The increased output would also increase the solar wind, possibly destabilizing the orbits even sooner (although that may cause them to slow and fall in). Credit to barbecue's parasite answer for inspiration!

Answer 10

I've got one that might be a bit out there. Imagine someone was tweaking the global constants of the universe - and some strange side effect was that helium atoms began decaying/unraveling/disappearing. It doesn't have to be rapid - 100 years gives a lot of time for the decay to occur over.

Our sun is currently 25% helium, but it doesn't take a lot to imagine a star a bit further along in its lifecycle and being ~50% hydrogen, ~50% helium. If a star like that started slowly losing atoms of Helium from the core (the helium would be in the center, not around the outside), it would slowly start shrinking, slowly start dimming, and slowly start losing some of its gravitational pull.

The nice thing is: Helium is pretty darned rare outside the sun (the reason it's called Helium is because we hadn't even found any of it on earth before we found it in the sun!) It's not like the stuff dissolving over 100 years on our planet would be any sort of catastrophic event.

Answer 11

With a description like "the exact details and claims are ambiguous, lack mathematical formalism, and often vary from one delusional crank to the next.", the Electric Universe model might come in handy for this question.

The Sun isn't a huge nuclear fusion reaction, it's a small one, the energy output and (by the powers of Handwavium) the gravitational pull are mostly an electric current flow from the center of the galaxy with the Sun as a light-bulb style node in an enormous circuit. As the galaxy rotates and the stars within it change relative positions, and the effects of frequencies combining or cancelling out, the amount of power flowing into The Solar System on a timescale of oh, say, a millennium or two can vary a lot.

Effects of such a drop include: A, B, C, D, E, F, H, and possibly G depending on how strict you are about "the ejected mass [..] must be dispersed into the galactic void." since there is no ejected mass, only a surprisingly small core of Sun remaining, with reduced visible size, reduced power output, reduced gravitational pull - maybe .. 50%?, and presumed reduced mass if that's even relevant anymore.

Searching YouTube for "the electric universe" will show many 'documentaries' and talks to give you more related ideas, such as Thunderbolt of the Gods

Bonus idea: classic fusion stars can exist alongside the electric conversion stars, so your other solar systems can be entirely normal, the Solar System happens not to be one of them.

as-yet-unknown but plausible scientific concept.

Uhh, I have no comment at this time, thank you.

Answer 12

There is the starlifting mentioned here, https://en.m.wikipedia.org/wiki/Star_lifting The explanation I have found is a bit vague, but it's basically called "huff-n-puff" alluding to the cyclical on and off. You make particle accelerators interact with the sun's magnetic field and cause mass ejection at the poles. This is eminding me of the ejecta from a black hole or a gamma ray burst. This ejecta makes the star lose mass rapidly.

Edit: although will work, it will be much harder to adjust orbital speeds of the planets.

Edit: a de-orbiting of satellites is possible via tethers which interact with Earth's magnetic field, create an electric current from orbital velocity and hence reduce satellite's speed until it falls back into the atmosphere and leaves no space junk. In a similar ways, an advanced civilization may employ space elevators with tethers. They will interact with the sun's magnetic field and gradually slow down their planet, to make-up for the decrease of mass of their star, and prevent their planet from slingshotting into deep space. https://m.phys.org/news/2014-05-tether-solution-satellite-de-orbiting-reentry.html

On the other hand, we should not interfere with the planet's rotation. Few tethers will get an artificially-generated current when at the right angle and maintain rotation that was previously lost.

Answer 13

It sounds like you're trying to get the planets to escape velocity of their star without destroying life on them. Tampering with the star at all, as others have mentioned, is improbable and extremely dangerous to life on those planets.

Perhaps a simpler, yet different approach to your goal here would work. What if instead, a rogue planet or other high mass body (such as a black hole or brown dwarf or something) made a close flyby of the planets in question, giving them a gravitational assist that flings them past escape velocity of the parent star?

This should be relatively safe, compared to modifying the star itself.

Answer 14

I'm not sure if this constitutes a complete answer, but I had a thought that mainly focuses on [E,F,G], while probably satisfying all of your other conditions.

When physics students start to learn about gravitational potential, one of the first problems they are asked to solve is the gravitational force inside and outside of a hollow spherical shell of uniform mass density. The results are maybe a bit surprising:

Inside - The net force from all parts of the shell is zero, essentially the same as if the shell didn't exist. This usually leads people to the "are we in a giant cosmic shell" question.

see: http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/sphshell2.html

Outside - The net force from all parts of the shell is the exact same as if the mass of the shell were concentrated in a point at its center. This result is the same for a spherical body with radially symmetric mass density. We approximate all celestial bodies as such, unless we are doing things like precision orbit determination for near-Earth spacecraft in which case we need to be more precise.

see: http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/sphshell.html#wtls

Ok, you may see where I'm going with this now. Say for some reason the sun ejected half of its mass in a roughly radially symmetric manner - that is spreading out in all directions roughly equally. And for now let's assume the ejected solar matter wont harm anything it passes across (I know I know, I'll come back to it). As the 'shell' of solar matter expanded, anything outside its radius would continue to move as if the sun were still a coherent body (see 'outside' result). As the radius of the 'shell' passed you, you would pretty much immediately begin to only experience gravitational force from the half mass of the sun that stayed centrally located in the solar system (see 'inside' result). So, with the (ridiculous) assumptions made so far, this is a gravitationally sound scenario in which your orbital velocity would immediately become escape velocity.

Now let's look at the issues with this answer:

1) How does this happen? I'm not a nuclear physicist or even slightly versed in heliophysics so I will try not to pull anything out of my butt here. However if you're ok with a vagueish handwave you could go with some abrupt change in the sun's internal cycle causing an ejection of this magnitude. Even better, I'd bet there's an answer here that would lend a ceedible explanation to this scenario.

2) Won't the ejected solar matter destroy everything it encounters? Yes, yes it will. The best way to address this would be to have the expanding shell begin to self-gravitate (start to form small clumps) as it expands. At the large scale the gravitational solutions are probably still valid (or valid enough) and this gives a plausible way for Saturn to avoid incineration by just being lucky enough to miss the now clumpy expanding 'shell' of solar mass.

3) If Saturn passes back outside of the shell on its way out of the solar system won't it again be captured by the combined mass of the sun and its ejecta? Yes. I think for this to work, the 'shell' would have to be ejected at a velocity higher than Saturn's eventual escape velocity. In this way, it will always be inside the 'shell.'
*This actually provides an interesting side opportunity in your narrative. As the 'shell' begins to self-gravitate and form clumps of ejecta all moving out into the void, maybe Saturn could fall into an orbit with one of these chunks. I doubt natural fusion would still be happening, but it would certainly be a lot of good fuel for man-made fusion (that has to be how your colony survives, right?).