Need Some Scientific Facts For an Idea of Mine

[daniel l.]

Okay, so I have this idea for a Sci-Fi story called Blackout. And I'd like some of the super smart people here to tell me if this can happen, and if so, how will it happen?

Basically, the story goes like this:

In the near future, radio astronomers begin to detect strange signals coming from nearby stars. The signals are continuous, repeating patterns. At first, thought to be alien transmissions, that hope is turned to terror when the signals begin to get louder and louder, culminating in the stunning and horrifying collapse of the entire star into a black hole -- the final process itself taking only an hour.

This happens several times over the decades, the star-killing phenomenon getting closer and closer to Sol. Finally, it is reported to the horror of all humanity that these signals are now coming from our sun and that we have only twenty years before the collapse.

 

So here's how I imagine the collapse happening:

1. Some sort of unexplained force starts compressing the star, this process takes an hour.
2. As the star gets further and further squished, the added friction creates more heat, and the fusion process becomes more powerful.
3. As it shrinks, the star gets exponentially brighter (somewhere in the range of several thousand times), in the process vaporizing the innermost planets and melting the crust off of those further out, sterilizing the entire system.
4. Finally, the star can't be squeezed any further, and it collapses into a black hole, plunging the entire remaining solar system into darkness.

 

So what I'd like to know is: How bright will the Sun get as it's squished? What is the curve for that? And what will happen to planets and moons based on their distances? Will Mercury be vaporized? Earth and Luna melted? Will Jupiter's atmosphere be blown away? Are Uranus and Neptune safe? These are all things I'd like to know.

[Scotius]

Well, first of all: Sun is too small to collapse into a black hole. Red giant and then white dwarf is the most likely final outcome of our star's life. But you are using space magic anyway, so... Mercury may not survive. Venus and Earth will be stripped of their atmospheres and burnt to cinders - but they will still be there as planets. Same for Mars probably. Jupiter and the rest of gas giants probably will be untouched. Though smaller satellites of Jupiter and Saturn might be in trouble - increase in solar energy can cause a partial meltdown and escape of volatiles.

[Wjolcz]

Not to bash your idea but you might as well add mutated neutrinos or monoliths to the story. But then the monoliths from 2001 weren't indestructible because one of them got hit by a meteorite and got damaged so they would probably not survive the interior of the Sun. Also, why does it have to involve some sort of catastrophy? I mean, I know a lot has been already invented by the Sci-Fi genre and it's hard to come with some interesting ideas (I'm struggling to come up with anything on my own tbh) but if I was to write a story I would make it about humans and how they deal with stuff. Part of the reason why I like The Martian and The Expanse so much is because of its complexity and how humans interact with their environment instead of "The Sun/Earth's core is dying and we need to drop nukes on it to reignite it". Maybe try something semi-realistic like that. There's really not many options left when your star is about to die/explode. Either just get the hell out of your solar system or build fusion reactors and rely on that.

BTW, don't stars get brighter because they get bigger not the other way around? The more surface for light to escape from the birghter it should be, right?

[KG3]

25 minutes ago, Wjolcz said:

BTW, don't stars get brighter because they get bigger not the other way around? The more surface for light to escape from the birghter it should be, right?

A star like the sun will get bigger as it goes into it's red giant phase.  As the interior of the sun heats up the outer layers will get fluffed up and expand, the surface will be cooler and redder.  

7 hours ago, daniel l. said:

1. Some sort of unexplained force starts compressing the star, this process takes an hour.
2. As the star gets further and further squished, the added friction creates more heat, and the fusion process becomes more powerful.
3. As it shrinks, the star gets exponentially brighter (somewhere in the range of several thousand times), in the process vaporizing the innermost planets and melting the crust off of those further out, sterilizing the entire system.
4. Finally, the star can't be squeezed any further, and it collapses into a black hole, plunging the entire remaining solar system into darkness.

I think you are right that compressing a star would make it brighter but you might run into some troubles with the amount of time you are talking about.  Stars are generally really big so any event that affects the entire star might take a bit longer than an hour. 

  Another thing to consider would be conserving the angular momentum of the star's rotation.  As the star gets "crushed" it would start spinning faster and faster, probably causing some really crazy things to happen with it's magnetic fields.  You also might get some kind of gravitational wave signal detected at LIGOS of the event.  

I have a hard time buying the idea that a stellar process could be "contagious" between stars.

Also, if this was happening in our little corner of our galaxy chances are we would have detected the same thing happening somewhere else in the universe.  

  Good luck with your story!

[Wjolcz]

7 minutes ago, KG3 said:

A star like the sun will get bigger as it goes into it's red giant phase.  As the interior of the sun heats up the outer layers will get fluffed up and expand, the surface will be cooler and redder.  

I'm aware of this but redder =/= brighter so this doesn't answer my question. I'm sure it's not just the case of bigger = birghter because it also depends on the spectrum of the star. Red dwarves are bright but in infrared spectrum (like Proxima Centauri). Unless we're assuming the spectrum doesn't change then I'm pretty sure if the Sun shrunk and kept the same spectrum it would actually lead to an ice age on Earth.

Also, are we assuming this catastrophic phenomenon turns the Sun into a fully convective star like red dwarves? If so then the X-rays from the core would get blasted out and wreak havoc in Earth's atmosphere.

Do keep in mind I'm not any kind of cosmologist so anything I write here might be wrong.

[kerbiloid]

Alien stellar parasites invade into stars, suck their elecromagnetic field, and as nothing can withstand gravitation, contaminated stars collapse, at any mass.

The repeating patterns are their chewing.
Black holes are their cocoons.
"The Invasion of Light-Sucking Cocoons."

Edited June 30, 2018 by kerbiloid

[GoSlash27]

I like the concept

If you're burning up billions of years of hydrogen in just an hour, then the radiation (light and others) would be billions of times higher. I'd compare the brightness to the interior of an h-bomb, except even an h-bomb isn't *that* bright.

I think you'd have a difficult time describing the effects.

As was pointed out by Scotius, the sun lacks the mass to collapse into a black hole under it's own weight. *However*, whatever is compressing it may be strong enough to pack it into it's own Schwarzschild radius.

Good luck on the story!

[KG3]

I think you might also briefly see jets at the polls of the stars as they collapse.  

https://en.wikipedia.org/wiki/Astrophysical_jet

[vger]

12 hours ago, Wjolcz said:

I'm aware of this but redder =/= brighter so this doesn't answer my question. I'm sure it's not just the case of bigger = birghter because it also depends on the spectrum of the star. Red dwarves are bright but in infrared spectrum (like Proxima Centauri). Unless we're assuming the spectrum doesn't change then I'm pretty sure if the Sun shrunk and kept the same spectrum it would actually lead to an ice age on Earth.

Also, are we assuming this catastrophic phenomenon turns the Sun into a fully convective star like red dwarves? If so then the X-rays from the core would get blasted out and wreak havoc in Earth's atmosphere.

Do keep in mind I'm not any kind of cosmologist so anything I write here might be wrong.

No, it's the opposite. Bigger = dimmer. Generally-speaking. There are some stars out there that are both big and bright. But I'm inclined to agree that if you could somehow compress the sun like squeezing an egg, it would get brighter and hotter.

[ARS]

Most stars are found along something called the Main Sequence, characterized by their balance between inward gravity and outward pressure generated by hydrogen fusion. Other stars exist that are off of it and fusing other elements, or else are dead or dying. These types have varying letters (spectral classifications) applied to them, with numerical sub-groups and a corresponding informal color (you can see the color in a good telescope). The higher up the scale, the bigger (and brighter) the star, but the faster the rate at which the hydrogen in them is used up and so the shorter their lifespan. For a number of reasons, very large stars - called giants, supergiants and hypergiants - like to live at the extreme ends of the spectral scales. Giant stars really do not like to be classes F or G, seeming to stay there for a very short time while heating up or cooling down to either extreme. There are a few known, but are decidedly in the minority. In general, most of the visible giants are either class-M or rather cool class-K (Betelgeuse, Arcturus) red giants, or class-B (Eta Carinae, Rigel, Deneb) blue giants. Main Sequence Classifications, in order from hottest to coolest:

O – Blue-violet stars. The hottest and most massive main sequence stars, with most of their energy output in the ultraviolet regions of the spectrum. Pretty rare, but also conspicuous. Delta Orionis and Zeta Puppis (Naos) are examples.

B – Blue-white stars, e.g. Rigel, or all the bright stars in the Pleiades.

A – White stars. Sirius A and Vega are examples.

F – Yellow-white stars. Upsilon Andromedae and Procyon are of this type. Canopus is a rare class F giant.

G – Yellow stars. The most famous is a G2V type known in Latin as Sol, and in English as The Sun. Alpha Centauri A, Tau Ceti and Zeta Reticuli are this type as well.

K – Orange stars. Alpha Centauri B, Epsilon Eridani.

M – Red dwarf stars. Have very long life-spans i.e. a trillion years. Proxima Centauri and Barnard's Star are of this type. Luminosity class is always V or VI, as more massive types are actually red giants, an entirely different kind of creature.

If you want to memorize the above sequence, use a handy mnemonic like "Oh Be A Fine Girl, Kiss Me" or "Oh Big And Ferocious Gorilla, Kill Mikey." Compressing the sun would likely increases the pressure inside, which, if I predicted correctly, would increase the luminosity and thermal output

[Just Jim]

21 hours ago, daniel l. said:

This happens several times over the decades, the star-killing phenomenon getting closer and closer to Sol. Finally, it is reported to the horror of all humanity that these signals are now coming from our sun and that we have only twenty years before the collapse.

I like the idea.... 

[Gargamel]

22 hours ago, Scotius said:

Well, first of all: Sun is too small to collapse into a black hole.

Under it's own mass.   But if there is a mystical outside force acting on it, then I see no reason (within the realms of sci fi) that it cannot.   Stellar mass and smaller black holes are theorized to exist. 

But an hour seems a bit fast.    I haven't done any of the math, but anything traversing a solar radius within an hour might be experiencing some relativistic effects.  This might be a good thing though.    But it also means that you probably have a force that can accelerate material to a fraction of light speed (Ok I just did the math, about 16% of the speed of light), and also push against the outward force of the star itself, and then against the quantum forces that keep atoms from collapsing, is a pretty strong force.   

Edited July 1, 2018 by Gargamel

[kerbiloid]

Someone would estimate the energy required to force a Sun to collapse, while it's desperately attempts to uncollapse back.

Can't do this myself, but wouldn't such energy be comparable to an energy to addd 1.5 M_Sun more.
If so, they wouldn't need the original Sun, they could be making blackholes right from the interstellar gas.

[daniel l.]

3 minutes ago, kerbiloid said:

Someone would estimate the energy required to force a Sun to collapse, while it's desperately attempts to uncollapse back.

Can't do this myself, but wouldn't such energy be comparable to an energy to addd 1.5 M_Sun more.
 If so, they wouldn't need the original Sun, they could be making blackholes right from the interstellar gas.

I'm not really speculating on motivations right now. I can just chop it up to being a weird phenomenon or hyper-advanced aliens of unexplainable motives -- it's SF you know.

What I'd kinda like to know, however, is how much damage could such a process do. Aside from the freezing, the comes after the collapse, the process itself would cause the collapsing star to brighten exponentially, and cook everything within range. But what is that range? Which planets would survive, which wouldn't, and what would the effects on them be? Blown-away atmospheres? Melted crust? Vaporized?

I want to be as scientifically accurate about these effects as possible.

[vger]

5 hours ago, ARS said:

O – Blue-violet stars. The hottest and most massive main sequence stars, with most of their energy output in the ultraviolet regions of the spectrum. Pretty rare, but also conspicuous. Delta Orionis and Zeta Puppis (Naos) are examples

Well, dang. Somehow I never knew that O-class emitted primarily UV. Heh... too bad they don't look like black lights in the sky
 

2 hours ago, daniel l. said:

I'm not really speculating on motivations right now. I can just chop it up to being a weird phenomenon or hyper-advanced aliens of unexplainable motives -- it's SF you know.

What I'd kinda like to know, however, is how much damage could such a process do. Aside from the freezing, the comes after the collapse, the process itself would cause the collapsing star to brighten exponentially, and cook everything within range. But what is that range? Which planets would survive, which wouldn't, and what would the effects on them be? Blown-away atmospheres? Melted crust? Vaporized?

I want to be as scientifically accurate about these effects as possible.

Is the "force" going to keep the star compressed after it reaches singularity size,  or does it terminate at that point? Considering that the sun's mass isn't actually being increased, would it be a stable black hole even if you could somehow do this? Seems like turning off the force would just cause the star to immediately go supernova.

 

 

Edited July 1, 2018 by vger

[daniel l.]

12 minutes ago, vger said:

Is the "force" going to keep the star compressed after it reaches singularity size,  or does it terminate at that point? Considering that the sun's mass isn't actually being increased, would it be a stable black hole even if you could somehow do this? Seems like turning off the force would just cause the star to immediately go supernova.

 

The force goes away once the squeezing is done and the star has become a bottomless pit.

A stable black hole can exist at any mass, though smaller ones have shorter lifespans due to decay by Hawking Radiation. So you could theoretically compress anything into a black hole.

Everything is held together and apart by certain forces. Enough gravity, however, can overwhelm those forces. Enough gravity can collapse the electrons of atoms onto their nuclei. Whenever an electron collides with a proton, it forms a neutron. So this process of collapsing atoms will create a body of solid neutrons of extreme density.

But even there it doesn't quite end. Enough pressure and you can break the forces holding those particles together until there's physically nothing left but a single point of infinite density. Nobody even knows what a singularity is made of, I think.

[KG3]

2 hours ago, daniel l. said:

What I'd kinda like to know, however, is how much damage could such a process do. Aside from the freezing, the comes after the collapse, the process itself would cause the collapsing star to brighten exponentially, and cook everything within range. But what is that range? Which planets would survive, which wouldn't, and what would the effects on them be? Blown-away atmospheres? Melted crust? Vaporized?

  Ok, your talking about several billion years worth of the sun's fusion taking place in minutes... cool!  It would be interesting to view this from the night side of the moon (viewing it from the night side of the earth might be complicated by the earth's atmosphere and oceans on the daylight side wanting to leave the planet in a hurry).  As this tsunami of photons travelled past the moon you would probably be broiled by light reflected by light reflecting off everything else in the solar system.  Most of this material is concentrated within a disc surrounding the sun.  Asteroids and planets would appear to brighten many times than the (normal) sun.  Zodiacal light is sunlight reflected off of dust orbiting the sun and is visible as a faint glow at certain times of the year would become deadly bright as well.  https://en.wikipedia.org/wiki/Zodiacal_light

Ok here is an XKCD what if that talks about what would happen if everyone on the earth pointed a lazar pointer at the moon.  At the end of the article he takes it to ridiculous extreme and vaporizes the surface of the moon.

     https://what-if.xkcd.com/13/

    

[kerbiloid]

If indeed take this assumption as given, that total energy of Sun radiation gets released at once (sounds reasonable for me), then:

Say, 3.83*10²⁶ W * 6*10⁹ yr * 365.2422 d/yr * 86400 s/d = 7.3*10⁴³ J.

At 1 AU from Sun energy density = 7.3*10⁴³ / (4 * pi * (1.5*10¹¹)²) = 2.6*10²⁰J/m².

***

So, Earth receives 2.6*10²⁰ * pi * (6.37*10⁶)² = 3.3*10³⁴ J.

Energy per mass = 3.3*10³⁴/6*10²⁴ = 5.5*10⁹ J/kg.

Vaporization heat ~  several MJ/k, i.e. negligible

If convert this into kinetic energy, this corresponds to speed ~= sqrt(5.5*10⁹ * 2) = 105 000 m/s = ~100 km/s,

I.e. Earth would become a dissipating hot gas cloud, escaping from Solar System.

***

So, Jupiter receives 2.6*10²⁰ * pi * (70*10⁶)² / 5.2²= 1.5*10³⁵ J.

Energy per mass = 1.5*10³⁵/(318*6*10²⁴) = 80*10⁶ J/kg.

Vaporization heat is negligible

If convert this into kinetic energy, this corresponds to speed ~= sqrt(8*10⁷ * 2) ~= 13 km/s,

I.e. Jupiter has survived, but has partially lost its upper atmosphere.

[daniel l.]

4 minutes ago, kerbiloid said:

If indeed take this assumption as given, that total energy of Sun radiation gets released at once (sounds reasonable for me), then:

 Say, 3.83*10²⁶ W * 6*10⁹ yr * 365.2422 d/yr * 86400 s/d = 7.3*10⁴³ J.

 At 1 AU from Sun energy density = 7.3*10⁴³ / (4 * pi * (1.5*10¹¹)²) = 2.6*10²⁰J/m².

 ***

So, Earth receives 2.6*10²⁰ * pi * (6.37*10⁶)² = 3.3*10³⁴ J.

Energy per mass = 3.3*10³⁴/6*10²⁴ = 5.5*10⁹ J/kg.

Vaporization heat ~  several MJ/k, i.e. negligible

If convert this into kinetic energy, this corresponds to speed ~= sqrt(5.5*10⁹ * 2) = 105 000 m/s = ~100 km/s,

I.e. Earth would become a dissipating hot gas cloud, escaping from Solar System.

***

So, Jupiter receives 2.6*10²⁰ * pi * (70*10⁶)² / 5.2²= 1.5*10³⁵ J.

Energy per mass = 1.5*10³⁵/(318*6*10²⁴) = 80*10⁶ J/kg.

Vaporization heat is negligible

If convert this into kinetic energy, this corresponds to speed ~= sqrt(8*10⁷ * 2) ~= 13 km/s,

I.e. Jupiter has survived, but has partially lost its upper atmosphere.

Holy... wow.

And what about Neptune? Could somebody living on (or inside) a moon of Neptune survive? If not, how far out would somebody have to go to survive either in the open or living underground inside an asteroid, moon, or dwarf planet?

[ARS]

3 hours ago, daniel l. said:

What I'd kinda like to know, however, is how much damage could such a process do. Aside from the freezing, the comes after the collapse, the process itself would cause the collapsing star to brighten exponentially, and cook everything within range. But what is that range? Which planets would survive, which wouldn't, and what would the effects on them be? Blown-away atmospheres? Melted crust? Vaporized?

We humans evolved on, and (so far) all grew up on, Earth. We instinctively expect the air to be breatheable, the temperature to be liveable, the gravity to be 9.8 m/s2, the days to last 24 hours, trees and grass, animals and plants and fungi, et cetera, et cetera.

The sad fact is, though, that no other planet we've detected thus far is even remotely habitable by human standards. The bigger ones are Jupiter-like balls of gas, while the smaller ones are almost universally airless balls of rocks or balls of ice. The few worlds we've found that do have both an atmosphere and a solid surface have been blanketed in gases that no human can breathe, at pressures anywhere from near-vacuum to 90 times Earth's sea level. While it's theoretically possible that a planet out there might harbor life as we know it, it would have to fit a long, narrow list of parameters, and even then, the kind of life that might have actually evolved there will most likely be very different from the multicellular-eukaryote-rich biome inhabiting Mother Terra.

In order for a planet to be able to support life as we know it on its surface at all, it will have to lie in a very narrow range of distances from its parent star. Too close, and any water would evaporate. Too far, and any water would freeze. Liquid water — and life as we know it requires liquid water — can only exist if the planet lies within that narrow zone where it's receiving just the right amount of energy from its star for the surface temperature to allow it. This is called the star's "comfort zone," or "Goldilocks Zone" (as in: not too close, not too far, but juuuuuuuust right). The exact width of a star's Golilocks zone is a matter of some debate, due to the fact that some atmospheres can trap heat (Venus) and some can't, and a number of other factors that astrogeologists can make whole careers out of. All we can say for sure is that, for a star as bright and hot as the sun, Venus is too close, Earth is clearly within the Goldilocks zone, and Mars is probably close to the tail end of it.

How far away from the star the Goldilocks zone is depends on the star's energy output. A very dim red dwarf star, like Wolf 359, would require a planet to be only about 1.5 million kilometers away from it to receive as much energy as Earth does from our sun — that's only 0.01 A.U., 1% of the Earth-sun distance. A bright and powerful star like Sirius A, on the other hand, would require a planet to be 5 A.U. away from it to receive as much energy as the Earth does from the sun.

Interestingly, both of those distances have potentially disastrous consequences. If a planet is only 0.01 A.U. away from its star, the star's tidal influence is going to be enormous. The strength of tidal forces varies directly with the larger object's (i.e. the star's) mass, but inversely with distance cubed. The tidal forces on a planet only 0.01 A.U. from a star 1/10 the mass of the sun are, therefore, going to be 0.1 / 0.013 = 100,000 times as strong as the tidal forces the Earth experiences from the sun. This all but guarantees that the planet will be locked in synchronous rotation with its star — that is, its rotational period must match its orbital period, so the same side is always facing the star. One side of such a planet would be in perpetual daylight, while the other would be in perpetual night. The climate on such a world would be much different than the climate on Earth.

Dim stars also have the disadvantage that their Goldilocks Zones are going to be narrower. There is disagreement as to exactly how wide the Goldilocks Zone around the sun is — different models compute widths anywhere from 0.5 A.U. down to 0.02 A.U. — but however wide the zone actually is, it will be proportionally narrower with a dimmer star (and wider with a brighter star). The star 61 Cygni is about 1/10 of the sun's brightness, so its Goldilocks Zone will be (the square root of 1/10) of the sun's, or a little less than 1/3 of the sun's Goldilocks Zone distance. But this means both the inner edge and the outeredge of the Goldilocks Zone will be 1/3 of the distance compared with the sun — and that means the zone as a whole will only be 1/3 as wide. The narrower the Goldilocks Zone, the less a chance that a planet would happen to have formed within it.

Worse, many red dwarf stars — Wolf 359 included — are flare stars, which emit semi-regular bursts of X-rays every bit as powerful as those emitted from a flare taking place on the sun. At 0.01 A.U., that much ionizing radiation can easily disassemble the organic molecules necessary for life. And X-rays can scatter. Regular flare outbursts so close by probably means that any life would have to be buried underground.

A planet orbiting Sirius A at 5 A.U. wouldn't have any of these problems, of course, but it runs into another issue. Sirius is a binary system. Sirius B (a white dwarf) makes one complete orbit around Sirius A every half century, and at one point in this orbit the two stars come within 8 A.U. of each other. As any budding astrophysicist will tell you, the three-body problem is a chaotic one for which there is no solution. Any planet orbiting Sirius A farther away than 1/4 of this 8 A.U. closest-approach distance will be thrown out of the star system by Sirius B's gravity. The farthest a stable planetary orbit can be from Sirius A is, therefore, only 2 A.U. — which is barely 2/5 of the Goldilocks Zone distance. Therefore, no planet can exist in the habitable, liquid water zone around Sirius A. (A planet could theoretically orbit both Sirius A and Sirius B as a pair, but then its minimum orbital distance has to be at least four times the greatest separation distance between the two stars in their orbit of each other. Sirius B's orbit is rather eccentric, and at one point in its orbit it's over 30 A.U. away from Sirius A. A planet orbiting both Sirius A and B would therefore need to be at least 120 A.U. away from their common center of mass, and at that distance the combined brightness of Sirius A and Sirius B would be far too weak to keep the planet from freezing.)

Even if a planet happens to lie within the Goldilocks Zone, that's no guarantee that it can harbor surface life — let alone that life will actually arise there on its own, or that said life will have had sufficient time to evolve to the point where space-faring beings can emerge. The atmospheric pressure must be high enough for liquid water to exist, and that can't happen unless the planet has sufficiently strong surface gravity to keep its atmosphere from escaping into space. You'll note that the Martian atmosphere is extremely thin, less than 1% of the surface pressure of Earth's atmosphere. One factor that contibutes to Mars's thin atmosphere is this low surface gravity. Despite being farther from the sun than the Earth, and thus receiving less heat that could potentially boil its atmosphere away into space, Mars still has less of an atmosphere than the Earth does. A resonably strong surface gravity may be required for a planet to retain a thick atmosphere. There are exceptions in our own solar system, of course: Saturn's moon Titan has less than a sixth of Earth's surface gravity yet its surface atmospheric pressure is higher than Earth's, and while Venus is both closer to the sun and has only 90% of Earth's surface gravity its surface pressure is ninety times that of Earth's atmosphere. But you need at least some gravity, and possibly quite a lot of gravity, to retain an atmosphere within the Goldilocks Zone.

Another factor that can mean no life-bearing planets are possible in a given star system is the lack of heavy elements. The Milky Way galaxy is over ten billion years old. When it first formed, it consisted almost entirely of hydrogen and helium; almost no heavier elements (like carbon and the other elements necessary for organic life) existed. Several generations of stars have been born and died since then, and some of the more spectacular star deaths have peppered the interstellar medium with heavy elements synthesized by those stars' death throes. The sun, for instance, is a third-generation star — the cloud of gas and dust out of which it formed contained material expelled by a supernova which, in turn, had formed out of an earlier cloud that contained material from an even earlier supernova. This is why there was enough carbon, oxygen, silicon, iron, etc. to form solid, rocky planets and organic molecules. Astrophysicists refer to all elements heavier than helium as "metals" (even if the element in question is oxygen or neon), and sometimes call a star system's heavy element abundance its "metallicity."

By contrast, Barnard's Star (a red dwarf approximately 6 light-years from the sun) formed in the Milky Way's first wave of star formation. It has almost no heavy elements. If the star itself is metal-poor, that means the cloud out of which it formed was also metal-poor, and therefore any planets that would have formed out of that cloud would be metal-poor as well. There might be some Jupiter-like balls of hydrogen or helium orbiting Barnard's Star, but there isn't going to be anything with a solid surface. So, to sum up, the requirements for a habitable Earth-like planet are:

1. The planet must lie within the Goldilocks Zone for its star.

2. The star cannot be too dim, since this will mean its Goldilocks Zone will be too narrow, any planet in the zone will be in synchronous rotation with the star, and the Goldilocks Zone will lie within the Danger Zone for stellar flares.

3. If a binary star system, the companion star cannot come closer to the primary than 4 times the Goldilocks Zone distance.

4. The star system cannot be metal-poor, or (if its metallicity isn't known) so old that it would have formed when the galactic medium was still metal-poor.

5. The planet cannot be too small or light, as this will prevent it from retaining an atmosphere.

Note that if you're willing to accept non Earth-like planets, many more possibilities open up. For example, Europa, one of Jupiter's moons, is thought to contain liquid water despite being nowhere near the Goldilocks zone. A thick or rapidly rotating atmosphere like Venus's can distribute heat evenly around the planet, thus solving the problem with tidal locking mentioned above. Greenhouse effect atmospheres, tidal heating from a nearby planet, and internal heating from other unknown mechanisms can all lead to potentially habitable conditions in unexpected places. However, these all lead to new problems and obviously won't resemble Earth.

For that matter, even liquid water might not be necessary. There are theories that life might be possible with alternate biochemistries based on liquid ammonia, methane, or even interstellar gases. Since all we have to go on is observations of Earth, there's no way to tell for sure if this is actually possible. But the less Earthlike you get, the more problems you have with an actual story involving anything other than Aliens. A hypothetical ammonia based organism, for instance, would constantly argue over the thermostat with Earthlings given that ammonia boils at -28F. 

If you want anything more interesting than bacteria to have evolved, another problem arises. The star must have been shining at roughly the same energy output for at least a couple billion years, in order to give time for complex life to have evolved.

This last requirement is a real buzzkill, as it eliminates damn near every bright star you can see in Earth's night sky. Big, bright stars like Sirius A only live for a few hundred million years before they run out of gas. (The candle that burns twice as bright lasts half as long, after all.) Red giant stars like Arcturus had a long, stable lifetime as a dimmer star in the past, but will only last for a couple of million years at the red giant stage — so if they did harbor life bearing planets in the past, those ecosystems were snuffed out when the star expanded to its current red giant state, and any planets in the star's newGoldilocks Zone won't have long enough for evolution to run its course.

As for our Sun, its core will run outta gas some 5 billion years from now, in the meanwhile, its luminosity will increase slowly as its core contracts to continue fusing the each time more and more scarce hydrogen. That will mean serious trouble for life on Earth in just around six hundred million years from now onwards. When this happens, the sun will inflate a lot. "But wait!" I hear you cry. "If the core is no longer providing any radiative pressure to support the sun's upper layers, why will it expand instead of shrinking under its own weight?" I'm glad you asked. When the core fizzles, the layer immediately above the core will collapse down upon it, and in the process this layer will get more and more compressed until it ignites in nuclear fusion itself, forming a hydrogen-burning shell. and consume at least some of the inner planets—likely including Earth, causing a solar system level apocalypse. Even if Earth survived, its fate would be to lose whatever water remains and atmosphere, becoming a planet covered by a magma ocean under the intense light of the huge red giant Sun. This inflation will take a time in astronomical terms and will be very gradual by human-lifetime standards: computer models of evolution of Sun-like stars suggest the sun will need more than 2 billion years to grow from its end-of-main-sequence normal size to its full red-giant glory. Delta Pavonis, a star extremely similar and very close—about 20 ly—to the Sun is currently going through this phase. It started the process during the time that modern humans have existed—possibly even during recorded history—but only our descendants to the umpteenth generation will get to see the transformation in full. Astronomers have a mild interest in this star, since being the Sun's "near-identical older brother"—as we put it—its evolution will give hints about what's to come for old Sol. After a couple of million of years in this red giant phase, it will shrink again in just a few thousand years as its core begins fusing helium into carbon and oxygen. Helium ignition is a very violent process, liberating energies comparable to that of a supernova. However, all of that energy is used to re-expand the core and nothing unusual is visible from the outside. The Sun will be then a red clump star, roughly fifty times as luminous as is now and eleven times larger, re-expand again as red giant (as an Asymptotic giant branch, to be more exact) when it runs out of helium at its core 100 million years later, and then finally shed its outer layers in a breathtaking display known as a "planetary nebula." So named because such nebulas appear as an extensive disc in a telescope, and can be confused for a planet by an observer who doesn't know any better. What will remain afterward is the tiny, exposed core of the sun, now shrunk to a super-dense white dwarf the size of the Earth, slowly cooling to a black dwarf over the next quadrillion years (more than 70 times the current age of the universe). More than a few astronomers and physicists have pointed out that at least by this point, the Sun will be harboring one big-ass diamond.

My prediction is, as the sun expands, the goldilocks zone would be pushed outward, roughly around the orbit of Saturn or Uranus, which could, theoretically make Titan habitable. Mercury and Venus is certainly being totally engulfed. As for gas giants, while the sun's size expands into red giant, it's temperature also become lower, so I cannot say for certain if the gas giants will be fully vaporized, but one thing is certain: gas giants WILL change. One of the theory why gas giants is so large is, since outer planets that's classified as gas giants lies on the outside of goldilocks zone, which is referred as "ice line". Water and other liquid froze, which causes them to expand in volume, so the planet-building material becomes larger, since it provides more material. So it's only a matter of guessing what's gonna happen to the gas giants if the "ice line" is pushed outward further. But I think @kerbiloid is right, Jupiter is most likely survived, albeit not like what it's used to be.

 

[Xd the great]

Well, as stuff gets squished together, fusion happrns more quickly, so  i would say thatthe Suns size remains the same after a bit of squishing.

The end point of fusions is iron, so i would imagine a lot of iron in the Sun.

Then, a supernova explosion, just smaller scale. Presumably blowing away half the solar system.

Then a neutron star, then a black hole.

I am just a kid, so these are not accurate.

[YNM]

Whatever your process is, it must continue to work until the Sun's radius is only 3 km or even smaller.

The Sun will get more and more brighter until it becomes insanely incredulously *bright* (mind the parenthesis) just before it's mass entered it's own scwarzschild radius.

So I guess not only the planets going to be "dead" because sunlight is no longer there, but the flash before it's demise will scour the face of every bodies in the Solar System.

Assuming the total lumimosity doesn't change, the last moment of Sunlight will occur with most of the peak wavelength at γ-ray wavelength, as the surface temperature will reach what today is Sun's core temperature (~ 15 milion K/deg C - doesn't matter this high up). Oddly enough this means the Sun will look "black" to the eye but it's been bombarding us with X-rays and γ-rays for some tens of minutes (wien law gives the max wavelength at 1 Å - for comparison blue light is 4000 Å).

But solar photon takes insane amount of time just to reach the surface, thanks to a phenomenon known as "random walk" and mean free path. So in the 1 hour collapse, it'll free up to hundreds of thousands or even millions of years of solar energy.

Assuming the mean free path means that it takes about 100,000 years for photons in the core to reach the surface, and assuming a constant radiation rate, the sun luminosity will reach 870 million times it's current lumimosity in the given hour. This gives an initial surface temperature of 1 million K... and an end temperature of 2.5 billion K. (at least it's not Planck temperature !)

So yeah, that is all bad news. In UV, X-ray and γ-ray.

Edited July 1, 2018 by YNM

[GoSlash27]

5 hours ago, daniel l. said:

And what about Neptune? Could somebody living on (or inside) a moon of Neptune survive? If not, how far out would somebody have to go to survive either in the open or living underground inside an asteroid, moon, or dwarf planet?

Well... even at Neptune, the flux is still on the scale of a thermonuclear warhead at point blank range... detonating continuously for an hour. Nothing can survive anywhere the light touches. Exposed regolith would probably heat to incandescence and fuse, but would probably not vaporize.
 You *might* be able to survive for a time if you're far enough underground, but I don't know how you'd survive in the long term.

Best,
-Slashy

[kerbiloid]

6 hours ago, daniel l. said:

And what about Neptune? Could somebody living on (or inside) a moon of Neptune survive? If not, how far out would somebody have to go to survive either in the open or living underground inside an asteroid, moon, or dwarf planet?

 

(With the same assumption about the total energy).

Neptune receives 2.6*10²⁰ * pi * (24.6*10⁶)² / 30.07²= 5.5*10³² J.

Energy per mass = 5.5*10³²/(17.2*6*10²⁴) = 5.3*10⁶ J/kg.

Vaporization heat is negligible

If convert this into kinetic energy, this corresponds to speed ~= sqrt(5.3*10⁶ * 2) ~= 3.2 km/s,

So, Neptune lost some part of the upper atmosphere.

***

Triton receives 2.6*10²⁰ * pi * (1.35*10⁶)² / 30.07²= 1.7*10³⁰ J.

Energy per mass = 1.7*10³⁰/2*10²² = 85*10⁶ J/kg.

Vaporization heat is ~3 MJ/kg, negligible.

If convert this into kinetic energy, this corresponds to speed ~= sqrt(85*10⁶ * 2) ~= 13 km/s,

Triton turns into a thick ring around the Neptune, with random icebergs inside,

***

Pluto receives 2.6*10²⁰ * pi * (1.2*10⁶)² / 39.4²= 7.6*10²⁹ J.

Energy per mass = 7.6*10²⁹/1.3*10²² = 58*10⁶ J/kg.

Vaporization heat is ~3 MJ/kg, negligible.

If convert this into kinetic energy, this corresponds to speed ~= sqrt(58*10⁶ * 2) ~= 11 km/s,

Pluto&Charon become a cloud of ice and rocks.

***

But happily, there is Jupiter. It's just 10 times smaller than Sun (70 000 km vs 700 000 km radius).
So, it shades up to 70/700*5.2 = 0.5 AU beyond its orbit.

And also there is Saturn.
It shades to 58/700*9.6 = 0.8 AU beyond its orbit.

Also Neptune makes a shade 24.6/700*30.07 = 1 AU deep.

And fortunately, the last phase of the Sun collapse was running very fast, and most part of this energy had been released in an hour or two,

So, once the Sun imploded, a little but brave Kuiperoid (or maybe that was even Pluto itself), was passing right behind the Neptune, in its shadow, 
Everybody who was on that lurking planet saw a blinding crown of flames around Neptune and lost eyes  and burnt wallpapers right throw the back of the head if were watching in telescope and said wow.

Neptune had eclipsed the planetoid, so it survived.
But gaseous clouds from vaporized icy moons, trojans, comets, whatever on its way have changed its orbit, sending it to pass by the former Sun.
Also its own ice was partially evaporated days earlier before it entered the shadow. This was like a reactvie jet. 

But a little closer that gaseous chaos made its orbit more round, though inclined (they can from time to time look at Solar System from above, what a happy coincidence!) and eccentric (they can withstand both heat and cold when its needed).

Somebody says, that Triton survived, too, by the same reason. But it's currently surrounded by a dense cloud ring of fluids evaporated from Neptune, so that's just rumors.

Another luck was that the former Sun is surrounded by gas-dust cloud of planet and crown remains, which is highlighted with X-rays from inside and shines in IR and even a little visible light.

Edited July 1, 2018 by kerbiloid

[GoSlash27]

8 hours ago, vger said:

Is the "force" going to keep the star compressed after it reaches singularity size,  or does it terminate at that point? Considering that the sun's mass isn't actually being increased, would it be a stable black hole even if you could somehow do this? Seems like turning off the force would just cause the star to immediately go supernova.

vger,

 Once the sun's mass is compressed inside a radius of 3km or so, it's immaterial whether the force stops or not; the effect is the same. It becomes impossible for any particle or photon to escape; every direction is inward.

Best,
-Slashy