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?
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.