Astronomers or Scientists say that Jupiter's Mass would have to be multiplied 80 times to become a star (M Mass). What if Jupiter was denser, would there be thermonuclear energy because of the density?
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$\begingroup$ How are you making Jupiter more dense? Are you replacing some of its hydrogen & helium with denser elements, eg iron? $\endgroup$– PM 2RingMar 26, 2021 at 16:09
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$\begingroup$ @PM2Ring Sure, Iron would do $\endgroup$– TardyMar 26, 2021 at 16:22
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$\begingroup$ But keeping most of the helium and hydrogen is necessary for thermonuclear reactions so let's just say we can make it denser by magic and temps $\endgroup$– TardyMar 26, 2021 at 16:26
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1$\begingroup$ Jupiter has a lot of H & He. Even if you replaced half of it, there'd still be plenty left. ;) A planet like that's unlikely to form naturally, but at least we could answer your question using science. It's tricky to give scientific answers to questions that invoke magic. $\endgroup$– PM 2RingMar 26, 2021 at 16:34
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To achieve thermonuclear fusion you need high temperatures and high density. If you were able (by magic) to compress and heat the core of Jupiter then fusion would occur.
But there is no mechanism that can cause Jupiter to increase it's temperature and density like this. In the core of a proto-star, gravity will provide the force needed to increase the pressure and density and the release of gravitational energy will provide the temperature to allow fusion to start.
Moreover, when fusion does start, the release of energy causes the core to stop contracting and prevents the density from continuing to increase. The release of fusion energy stabalises the collapse of the ball of gas, and allows stars to shine for perhaps billions of years. If you started fusion in the core of Jupiter (for example by setting off a nuclear bomb) it would cause that part of core to expand, lowering density and ending the fusion. The stable state for a body the size of Jupiter is to be a planet, not a star.
Increasing density by changing the composition to one with larger nuclei actually makes it harder to start fusion. Larger nuclei have a larger positive charge. This makes it harder to get them to fuse. So you need much higher temperatures.
So the only way for Jupiter to become a star is to increase it's core temperature and density. But that can't happen except by greatly increasing its size.
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$\begingroup$ Without sustained external pressure, the fusion will lead to an expansion to its original size and density because that is the stable situation. $\endgroup$ Mar 26, 2021 at 15:59
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$\begingroup$ @JamesK Yes, That is logical, Gravity and heat is basically the only astronomically way to sustain a celestial's body or star's density $\endgroup$– TardyMar 26, 2021 at 16:25
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$\begingroup$ I think if you increase jupiter's density 80 times you get a star $\endgroup$– TardyMar 26, 2021 at 16:29
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$\begingroup$ No, you don't because its not hot enough. And if you do make it hot enough and dense enough, the release of energy will rapidly cause it to expand, stop fusing, and cool. $\endgroup$– James KMar 26, 2021 at 17:08
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$\begingroup$ @JamesK But, The action of increasing density can increase heat, I already know it is not sustainable to increase density without gravity. $\endgroup$– TardyMar 26, 2021 at 21:53
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The minimum mass for a brown dwarf is about 12-13 jupiter masses, and averagely they're 75, so theres no chance that Jupiter would be a star at its current weight.
