Supergiant stars are the largest stars in the Universe. They are also the most massive, and most luminous stars in the universe.
Supergiants can have masses from 10 to 70 solar masses. And brightness from 30,000 up to hundreds of thousands of times the solar luminosity.
Supergiant stars, in general, give off between 10,000 and one million times the energy of our Sun.
They are anywhere between 30 to 1,000 times the radius of the Sun.
These gargantuan objects are old giant stars that are nearing the end of their life.
Betelgeuse is an example, a bright red supergiant star in the constellation Orion, visible to the naked eye, and with a diameter about 700 times that of the Sun and about 15 times as massive.
Unlike stars like our Sun, supergiants are consuming hydrogen fuel at an enormous rate and will consume all the fuel in their cores within just a few million years.
This means these types of stars live fast and die young. Their lifetimes are only 10 to 50 million years which is extremely short on the scale of stellar evolution.
Supergiant stars are only observed in young cosmic structures such as open clusters, the arms of spiral galaxies, and irregular galaxies.
They are generally classed as being either red or blue.
Red supergiants have a mass at least eight times that of our Sun and are generally old stars that were once similar in size to the Sun. Blue supergiants, on the other hand, are considerably hotter than red supergiants, but generally much smaller, only about 25 times the size of the Sun.
When supergiant stars die they detonate as supernovae, completely disintegrating themselves in the process.