When all of the hydrogen of the Sun is used up, it will turn into a _________?
When all of the hydrogen in the Sun is used up, it will turn into a different type of star called a red giant. To understand why, we need to know a little bit about the life cycle of a star.
Stars, including the Sun, are powered by nuclear fusion, which occurs in their cores. In the case of the Sun, it fuses hydrogen into helium, releasing a tremendous amount of energy in the process. This energy is what makes the Sun shine.
However, the Sun's hydrogen supply is not infinite. Eventually, it will run out of hydrogen fuel in its core. When this happens, the energy production in the core slows down, causing the core to contract under gravity.
As the core contracts, the outer layers of the Sun start to expand. The Sun will then evolve into a red giant, a much larger and cooler star. In this stage, the Sun's outer layers will engulf the inner planets, including Earth, making the conditions on our planet inhospitable for life as we know it.
During the red giant phase, some stars can undergo further fusion reactions using helium and other elements, but ultimately, the Sun will not have enough mass to ignite the fusion of heavier elements, like carbon. After the red giant stage, the Sun will shed its outer layers, forming a planetary nebula. The remaining core, called a white dwarf, will gradually cool down over billions of years.
So, to answer your question, when all of the hydrogen of the Sun is used up, it will turn into a red giant.