Red giants (Patreon)

Red giants are a type of star that is in the later stages of its evolution. They usually form from stars like our Sun when the star runs out of hydrogen in its core and begins the process of expanding its outer layers.

It causes the star to increase in size, becoming much more voluminous and bright. Red giants emit most of their energy in infrared wavelengths. This happens because the outer layers of red giants are rich in molecules and dust that absorb visible light (high energy) and emit energy in the infrared spectrum (low energy).

On the pic( the VLTI telescope): Antares is red supergiant, with a diameter 400 times larger than the Sun's.
If Antares were in the Sun's place, it would extend beyond the orbit of Mars and "touch" Jupiter.