Alex McColgan

And how are scientists going about trying to replicate the process?

Well, the first thing to consider is the reaction medium, the stuff stars are made of.

Unlike matter on Earth, stars aren't even made of atoms and molecules, where negatively charged electron clouds orbit positively charged nuclei.

Stars are so hot that electrons can escape atomic orbits entirely.

The resulting soup of charged particles, ions and free electrons is known as plasma, and it's in plasma that nuclear fusion can take place.

Now, plasma is by far the most common material in the universe, making up well over 99.9% of visible, that is non-dark, matter.

but we are part of the 0.1%, that small amount of matter in the universe that's cool enough that in general, electrons confined to orbitals and chemistry, not nuclear physics, dominates, allowing cool balls of rock covered in oceans of water like Earth to form.

For us, creating such conditions, making plasma that's hot enough to sustain fusion and containing it is a considerable challenge.

You see, the Sun has one quite literal giant advantage on its side.

The biggest fusion reactor on Earth, ITER in France, a leading international project that hopes to be operational in 2034, will use just a few grams of plasma material in a chamber of 830 cubic meters.

Because it's under such low pressure, meaning particles aren't squeezed together like they are in the sun, this plasma has to be much, much hotter to achieve fusion.

150 million degrees Celsius, as opposed to 15 million degrees at the core of the sun.

Now, fairly obviously, you can't just hold a material like this in a container made of normal matter.

If it contacted the sides, it would cool, electrons would condense into atomic orbitals, and it would no longer be plasma.

And of course, it goes without saying that the container itself would be damaged beyond repair, so the plasma needs to be isolated in a vacuum.

Two approaches have been put forward to achieve this, the first of which is magnetic confinement fusion.

Because plasma is a soup of charged particles,

positively charged ions and negative electrons, it can be manipulated by magnetic fields.

Magnetic confinement takes advantage of this by using a ring of powerful magnets to hold plasma in a continuous donut-shaped blob in which fusion can take place.

There are a number of different types, stellarators and reversed field pinch devices, but the leading design is called the tokamak.