Timeline for answer to My star will explode as a supernova. What can I do in order to ensure that my planet survives that? by Ovi
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| when toggle format | what | by | license | comment | |
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| Jul 21, 2016 at 4:56 | comment | added | a4android | @Ovi. Yes it would. My problem with moving BH's is that would be many, many orders of magnitude easier to move the planet to safety than moving BH's. Call it personal taste. | |
| Jul 20, 2016 at 11:46 | comment | added | Ovi | @a4android Yeah I was the only one who mentioned it in some above comments, I came up with it so we don't need a supermassive BH. But I think it could make sense for the reasons I've said above | |
| Jul 20, 2016 at 8:43 | comment | added | a4android | @Ovi if so, then a 3.8 Sol mass BH has the right size. However, I have scrolled through the question & the answers, but I can't find any reference about the "planet" being an asteroid. I could be wrong, if I am puncture my balloon. Asteroids would easier to protect. | |
| Jul 19, 2016 at 13:11 | comment | added | Ovi | @a4android Does it really need to be thousands of solar masses though? We said the "planet" might actually be just an asteroid a dozem KM in diameter, but the aliens called it their home planet just for us to sympathize with them more, or to make more sense as a religious object. Apparently there is a black hole with only 3.8 solar masses and a 24KM diameter, enough to cover an asteroid | |
| Jul 19, 2016 at 13:03 | comment | added | a4android | @Ovi Yes if it's a stable system. A BH big enough to shield the planet will be one thousand solar masses. When the BH approaches everything in the planetary system will swing into orbit around it. This will be chaotic. Star & planet could easily fall into the BH. The planet could be steered by thrusters & then hovers. But the trajectories would be insane. The fuel bill would be crazy. However, it doesn't violate physics. | |
| Jul 18, 2016 at 4:58 | comment | added | Ovi | @a4android Someone mentioned above that the minimum size of a black hole (which can be a few dozen KM across" is about 10 solar masses, and there are plenty of starts bigger than that. The star and the black hole can orbit a common center so that they don't crash into each other, and the planet can hover above the event horizon using thrusters and always have the BH in between the planet and the star. The BH's effects on the supernova could probably be taken into account mathematically by the aliens | |
| Jul 18, 2016 at 1:22 | comment | added | a4android | It's the gravity of the situation. Any black hole big enough to shield a planet will be hugely more massive than the star itself, which will be 10 soalr masses, let alone the planet you're trying to protect. Both star and planet will plunge into the black hole along with the rest of their planetary system. en.wikipedia.org/wiki/Black_hole suggests 10^3 solar masses for an approx. Earth radius BH. No go, But it would be good for eating the star. Just that everything else go would go too including the planet. | |
| Jul 17, 2016 at 23:43 | comment | added | MolbOrg | @Ovi not for both. I'm saying efficiency of energy extraction is higher in case when you drop something in to black hole, instead collecting energy from supernovae blast and you might use any star (not necessary supernova anything like Fe). Minimum for supernova is 10 sun masses, so dropping it in to BH will be 80 times(at least) more efficient then collecting all energy from supernova blast. Energy efficiency do not changes with size of BH, but ease of dropping and extracting energy changes and with bigger BH it's easier, because of size. Bigger it is, faster it can be feed. | |
| Jul 17, 2016 at 23:18 | comment | added | Ovi | @MolbOrg Not sure if i understood correctly, are you saying that you use more energy to create a black hole near a supernova than to travel to a galaxy which naturally happens to have a supernova and a BH close together? | |
| Jul 17, 2016 at 23:15 | comment | added | Ovi | high for any material known to man, but the OP said we can use anything as long as it doesn't contradict the laws of physics, and i don't think it would break the laws if some aliens had a super strong material | |
| Jul 17, 2016 at 23:13 | comment | added | Ovi | @Victor Stafusa We do not want a supermassive BH. We do want some of the radiation to lense directly towards the planet, because that's how we gather data. The nice thing is that the closer you are to the BH, the less radiation you will recieve. So you can fine tune your distance, and have as much radiation hit you as you can survive. Also, I don't think the planet will neccesarily reduce to a ring of dust. It doesn't have to orbit the black hole to not fall in. If it has powerful enough thrusters, it can just hover stationary above it. The spaghetification forces would be too | |
| Jul 17, 2016 at 21:56 | comment | added | Victor Stafusa | @MolbOrg - Hmm, well noted. This should be much less expensive than a supernova and much easier to be finely tuned/controlled. Also, it is much more reusable (it is an interesting science to make entire planets, stars, BHs and even entire galaxies as parts of some sort of giant machine, we need to find a name for that). Anyway, I will keep the "survive a supernova" challenge to not stop the party for everybody. | |
| Jul 17, 2016 at 21:29 | comment | added | MolbOrg | @VictorStafusa BH itself is better energy source then supernova. it's almost $\small 0.5 \times mc^2$ dropping sun mass in BH will (if extracted) generate 8 times more energy then hypernovae blast which is 1e46J, So if you up to energy only, better to think about that - no need in BH creation just travel to galaxy BH and drop near by suns there. With preparations it can be done. | |
| Jul 17, 2016 at 21:21 | comment | added | MolbOrg | @Ovi no, not hundred, size of BH is measured by event horizon, we do not know what is inside in with form etc, measuring arbitrary outside also makes no sense. Size is event horizon. There is no thickness - it's singularity or it's inside or it's outside. If greater distance is solution there are easier then BH approaches for that. | |
| Jul 17, 2016 at 20:33 | comment | added | Victor Stafusa | Anyway, making the planet a small asteroid shadowed by the BH at hundreds of AUs from the star is an interesting solution. I.e. Asteroid "planet" at L2 point of BH's orbit around the star. | |
| Jul 17, 2016 at 20:24 | comment | added | Victor Stafusa | ... However, if I have enough energy to maneuver a supermassive blackhole, then I would probably not need the supernova afterall, since it would be far easier to just use that energy instead to directly decrypt the data. Further, relativity will mess that idea in strange ways. | |
| Jul 17, 2016 at 20:22 | comment | added | Victor Stafusa | The bad side is that gravitational lensing would also lense supernova's radiation towards the planet. If we move the planet to be near enough the BH so the lense would focus significantly far away to the planet, tidal forces would desintegrate the planet making it be a ring of accretion around the BH spinning at relativistic speeds. For it being large enough to create a large enough umbra without destroying the planet, it will need to be a supermassive blackhole... | |
| Jul 17, 2016 at 19:06 | comment | added | Ovi | @MolbOrg Hm the radius of the black hole is a problem. But maybe the event horizon is a few hundred km think? I haven't been able to find a good source for the thickness of the event horizon. Also, maybe the aliens decieved us even more (to make the religion story more credible), and the the "planet" is just an asteroid a dozen km accross. Also, maybe they can adjust mathematically for the BH's effects on the supernova, or they can move 100-1000 AU away from the star, which is still quite close for a supernova | |
| Jul 17, 2016 at 18:30 | comment | added | MolbOrg | Gravitational lensing - exactly why using BH is't such brilliant idea. Shadow cone will be not geometric one. Depends trough on size of that BH but 10 solar masses is just 30 km radius. And that 10 solar masses near star might unpredictable to disrupt processes in star make explosion more asymmetrical and make things even worse for that particular direction. (hm, up for you thinking about that, but it might be not so easy - Jupiter affects Sun pretty noticeably from 5a.u. distances with 0.1% Sun mass) (sun cycles might be connected with $\small \sim$600km offset barycenter movements) | |
| Jul 17, 2016 at 15:09 | history | answered | Ovi | CC BY-SA 3.0 |