With all the fascinating planets in our solar system, it sometimes feels like the Sun gets overlooked. The Sun is amazing! People still worship the Sun, and that actually makes a certain amount of sense. So, what would happen if you took a small piece of the Sun and brought it back to Earth? Well, whoever's left would have new reasons to worship the Sun.
GIF Source: Kurzgesagt — In a Nutshell
The YouTubers behind Kurzgesagt have put together a solid video that explains the particulars of what would happen in this hypothetical scenario, and you really should watch it because the animation is great. For those who like simple answers in text form: The Sun would kill you.
But there's so much more to it than that. First of all, the way in which you'd die depends on which part of the Sun you brought back home. If you managed to get a sample of the chromosphere, the Sun's atmosphere, it wouldn't last very long. Because the chromosphere is a million times less dense than air, Earth's atmospheric pressure would crush our sample right away. But as air fills the vacuum, a high-pressure shock wave is created, and if you're too close to it, it will kill you.
The next layer of the Sun, the photosphere, gives off the brilliant light that fills our sky. A sample from it would also be less dense than air. But because its heat supports it, it wouldn't implode. Instead, it would briefly glow one million times brighter than the Sun as we see it from 150 million km away. A small enough sample to bring into a lab would burn everything in its general area to pieces, and then it would quickly cool to become a gas that's entirely safe. Of course, if you're in the general area when this all goes down, it will kill you.
Bringing back a sample from the radiative zone is when things start getting interesting. Assuming we've pulled our sample into the lab under the conditions that it existed in while it was part of the Sun, it would immediately lose the pressure that holds the plasma together, and the resultant thermonuclear explosion would blow up our lab, our city, and everyone in it — including you. You'd be dead.
The grand finale involves bringing back part of the Solar core. I won't spoil this but let me tell you, it's a much bigger deal than the other layers, and it will kill ya.