Our planet is puny compared to our sun.
Being from planet Earth and all, it's only natural that we should use our experiences as a baseline for what we observe beyond our solar system. For example, 1 sol is a unit of comparison to our sun (where 1 sol = 1 Earth's sun). I will be using this comparison to give you an idea of the size of hypergiants, I find it to be useful.
I suppose it's time that I told you just how big hypergiants really are. A hypergiant star can get up to 100-265 solar masses, which means that they can easily have diameters over 1,000 times that of the sun. That's big. The closest yellow hypergiant yet identified is in the "fried egg nebula", it's diameter would almost reach Jupiter if it were placed where our sun is now.
The Fired Egg nebula is actually two shells of debris surrounding a central yellow hypergiant.
There's an old saying, "the bigger you are, the harder you fall". This has never been more true than it is for hypergiants. Being so massive, the rate at which they burn through their fuel is amazing. Hypergiants can reach temperatures up to 50,000 Kelvin and output millions of solar luminosities (amount of light given off by the sun). All this means that hypergiants are relatively short lived stars, they may only live for a couple million years max, whereas our sun will live to the ripe old age of 5 or 6 billion years old.
When stars die, they often go nova, expelling their outer shells as they collapse in on themselves. As you might have guessed, hypergiants go hypernova. The death of a hypergiant star is one of the most powerful forces in the universe, with the power of over 100 supernovae. To give some perspective, Eta Carinae, the hypergiant star 75,000 light-years away, will give off enough light to read by at night when it goes nova.
By now it's only natural to be wondering how big stars can get. I often wonder that myself. So far, the largest star ever observed by man is VY Canis Majoris, weighing in at 15-25 solar masses. During it's main sequence, it may even have had a mass of 30-40 solar masses. VY Canis Majoris is by far not the heaviest star out there, but it has a radius of somewhere between 1,800 and 2,100 solar radii. It is certainly the largest.
VY Canis Majoris, not the heaviest, but certainly the largest.
The heaviest star known to man is R136a1, weighing in at a whopping 265 solar masses. This star also holds the record of the most luminous, being over 8,700,000 times as bright as the sun. I'm going blind by just thinking about it.
R136a1 seen in the R136 super cluster within the Large Magellanic Cloud.
The universe is a big place filled with big things. Objects like hypergiant stars really put things into perspective, and I'm betting that we find even bigger stars in the years to come.