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Inspired by this Kongregate game:

The TL;DR of the plot of the game is this: All life on Earth is dead, so shoot potatoes into the sun to make it a black hole, then orbit really close to the edge of the black hole, use time dilation to experience the end of the universe. Then use a misunderstanding of Stephen Hawking's "A Brief History of Time" to hit the end of the universe, travel back in time then save Earth.

Ignoring relativity in all aspects and time travel, the bit about potatoes got me thinking: if a comet crashes into The Sun it will clearly burn up, but if trillions upon trillions of comets crash into the sun, its mass could substantially increase.

Questions:

If I fire enough potatoes into the sun for its mass to double, what will happen to the nuclear fusion? will it be slowed down, or continue as normal?

Also, is it even possible for me to fire enough potatoes into the sun to make it become a black hole? or is a potato not dense enough/

Handwaving limit: Just ignore where this many potatoes are coming from and also the mechanism by which they are fired into the sun

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closed as unclear what you're asking by kingledion, L.Dutch, Aify, Mormacil, JDługosz May 10 '17 at 10:00

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ @gerrit I think there is a big of an issue with having a "handwaving limit" and a hard-science tag in one question, but I think that could be corrected by making an edit to take the handwavy terminology out. If we replace "fire enough potatoes into the sun" with "sending enough potato-like objects on a collision course with the sun" we get a hard-science question. It does take all the fun wording out, though. $\endgroup$ – Cort Ammon May 10 '17 at 0:13
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    $\begingroup$ If you tag hard-science and then include then include 'handwaving,' your question does not make sense. Where are you going to obtain/store a solar mass of potatoes? Voting to close as 'unclear what you are asking.' $\endgroup$ – kingledion May 10 '17 at 2:13
  • $\begingroup$ @kingledion The universe is big. If you really want to transport solar masses worth of potatoes, the universe just might be able to make your wish happen! $\endgroup$ – Cort Ammon May 10 '17 at 3:56
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You would need another 2 solar masses since the minimum size for a neutron star to collapse into a black hole is about 3 solar masses (2.7 to 3.2 solar masses as far as I have seen).

The density of the potato isn't the issue, just the mass.

The main problem that I can see is that you would have to act fast. As the potatoes burn up, they will be "poisoning" the Sun with carbon. When the ratio gets high enough, the carbon will get in the way of too many hydrogen or helium collisions. The might lead to a premature death of the Sun.

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  • $\begingroup$ Actually, the carbon will accumulate in the core, and eventually will combine with helium to form oxygen. $\endgroup$ – WhatRoughBeast May 9 '17 at 23:46
  • $\begingroup$ @WhatRoughBeast, That reaction has a much lower energy output. Speed would still be needed since it would start getting very cold and the core might collapse causing a mini nova that would ruin your day. Also, I'm not convinced that the carbon would get to the core very quickly. Just look at how long it takes light to get out. $\endgroup$ – ShadoCat May 9 '17 at 23:51
  • $\begingroup$ @WhatRoughBeast with all that energetic turbulence, how will the carbon migrate from the surface to the core? $\endgroup$ – RonJohn May 10 '17 at 2:07
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    $\begingroup$ Scientifically, these are all good points. However, the post is tagged as hard-science, and this answer is not. If a questions can't be answered in a hard-science manner (and this one can't), it shouldn't be answered at all. Reluctantly -1. $\endgroup$ – kingledion May 10 '17 at 2:15
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    $\begingroup$ @kingledion, you will notice that it is actually marked "Science Based". Please reread the original post. $\endgroup$ – ShadoCat May 10 '17 at 17:33
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This answer is an addendum to ShadoCat's answer. The problem is mass. The mass of the entire solar system is roughly one percent of the mass of the Sun.

Assuming you grow enough potatoes to convert the mass of the entire solar system into potatoes (super-scientific horticulture required). Then shoot all of them into the Sun (super-scientific mass driver technology and power sources required). The result will be that the mass of the Sun will have increased by a whopping one percent.

Mass Total (M) = mass of the Sun + mass of potatoes
= 100 + 1 % (masses as a percentage of the Sun's mass) = 101 %

The mass of a black hole necessary to meet the requirements of the question will be the equivalent of a stellar black hole

A stellar black hole (or stellar-mass black hole) is a black hole formed by the gravitational collapse of a massive star.1 They have masses ranging from about 5 to several tens of solar masses

Source: Stellar black hole

The mass of the Sun and a solar system converted into potatoes which were shot into the Sun to add its mass is only 1.01 solar masses. This is far too low to create a black hole. But launching potatoes into the Sun is something to do if you are the only survivor on a dead Earth, at least, until you also die, say, of old age or an accident during launching potatoes.

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The problem has nothing to do with mass and everything to do with heat.

The sun is hot[citation needed].

When looking at a giant star, they have more than enough mass to create a black hole. What stops them from collapsing into a black hole is called Radiation Pressure.

You may know already that hot things expand. Stars, being really really hot expand, A LOT. This means their density is not very high. For example the sun has a density of 1.4 x water. Even Earth has a higher density.

Interestingly, by adding more mass to the sun, we would increase the temperature by increasing the gravitational pressure, which would give more radiation pressure to support the star.

Assuming that a potato is made of pure sugar (well starch), then it is made up of Carbohydrates (Hydrogen, Oxygen and Carbon).

Interestingly enough, again, once the sun reaches approximately 1.3 solar masses in size (or 4 MegaKelvins), things become really interesting. The huge proportions of Carbon and Oxygen would being to catalyse the Hydrogen reaction using the CNO cycle. More heat in generated, resulting in radiation pressure.

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