There are some things in this universe that humans simply cannot comprehend, no matter how hard they try. Whether this is a result of the object’s innate nature or a limitation resulting from our narrow perception, these objects have always remained beyond our understanding. The concept of infinity is one of them. String Theory is another. Then you have this behemoth—the star, VY Canis Majoris (VY CMa). Its immense size will surpass anything you can envision, even in your wildest dreams.

Our star (the sun) is the perfect size—not large enough to overheat the earth and not small enough to freeze it. It provides just enough heat and light for life to thrive. For the early humans, the sun held tremendous respect and value. Indeed, some civilizations even said that it was the embodiment of a god. If you think about it, the sun is an incredible structure. It makes up nearly 99.9% of all the mass in our solar system! In fact, you would need 330,000 earths just to match the mass of the sun. Most of this mass comes from two key elements found in every star – hydrogen and helium. Stars have managed to harness the power of nuclear fusion (one of the greatest mysteries plaguing mankind today) to convert this hydrogen into helium. In this process, an unimaginable amount of energy is released.

So just how much is released? Let’s do some math (and imagining).

The atomic bomb dropped on Hiroshima releasing the same amount of energy as nearly 13.5 kilotons of TNT — the same as 13,500 tonnes of TNT. So right now, picture that gigantic atomic cloud shrouding the city and the force of the blast annihilating everything  in its path. Now multiply that picture in your mind by a factor of 75 — 75 times more dust, debris, and destruction. This gives you an image of a single 1-Megatonne bomb.

This is where it gets crazy. The sun releases the equivalent energy of 1,000,000,000,000 (one trillion) 1-Megatonne bombs. This is exactly what I defined earlier as “unimaginable”. No matter how hard you try, it’s impossible to even begin to picture this amount of energy. In fact, if we were able to harness all of that energy, we would be able to supply the needs of our civilization for the next 500,000 years. Now get this — the sun releases all of that energy in one second.

That’s right. One trillion 1-Megatonne bombs worth of energy per second! 

The phenomenon can be explained if we look at Einstein’s equation Energy = Mass x (Speed of Light)^2, aka. E = MC^2. Notice that the equation contains a constant: C^2. This means that for even an incredibly small mass, nuclear fusion releases a tremendous amount of energy because that mass is multiplied by 34,689,807,504. The derivation, as well as the explanation, of this equation will be covered in an upcoming article so stay tuned!

The astounding amount of energy released in such little time seems shocking right? Well that part was only the setup for the main attraction. Take a look at the “star” of the show, VY CMa:

You can try to imagine the amount of energy this giant releases, but I’ve already given up trying to bring it within my boundaries of my mind.

VY CMa is located in the Canis Major constellation, commonly represented as one of the “dogs” following  Orion, “The Hunter”. The star is located about 3,900 light-years from earth (about 22,907,207,980,800,000 miles). However as you can see, it’s most incredible feature lies within it’s dimensions, not distance. One of the most common methods for labeling the sizes of stars relies on how they compare to our very own sun. The unit, solar radius (SR), is equal to the current radius of the sun (432, 450 miles). This may seem like a gigantic number, but it’s nothing compared to the sizes of other stars. In fact, VY CMa has a radius of about 1420 SR, or 614,079,000 miles. That is, if you were to measure the distance from one end to the other through the center, it would be ”1 billlion, 228 million, 158 thousand miles” (diameter). Over a billion miles! In fact, if you were to replace our sun with VY CMa, it’s  radius would extend past the orbit of Jupiter!

Here’s another comparison to hit it home. Light travels at an incredible 186,282 miles per second. Well, it takes light about 0.1335 seconds to circle the entire Earth (at its equator) once. When circling around the sun once, light clocks in at about 14.58 seconds. However, to circle around VY CMa once, it takes light around 8.5  hours. In fact, when VY CMa was first discovered, astronomers thought there had been a mistake in their measurements since a star this big was “theoretically not possible”. That’s how big this thing is.

Whenever I talk about VY CMa, I like to end with a picture that truly represents the grandness of this star. When it explodes with all the beauty of a supernova, the universe will have lost one of it’s greatest prizes. But rest assured that VY CMa will never truly be gone. A star this big will continue to exist in the form of the universe’s most destructive, yet mysterious, force – a black hole…

Update (8/9/2012) :

I have seen a few comments regarding the title of my post. It is true that there may exist stars that are much larger than VY Canis Majoris that we have not yet found, which is why I added the “observable” into the title. However, there is an upper limit to how large stars can grow. This limit is known as the Eddington Limit.

The Eddington Limit forms it’s basis on the fact that all of a star’s nuclear fusion occurs at the core. The energy produced by fusion then “migrates” outwards towards the surface, and then escapes in the form of light. (This takes a very long time! The light that we see from the sun was actually produced by energy that was released anywhere from 10,000 to 180,000 years ago.)

At the core, tremendous amounts of pressure is constantly pushing outwards on the star. Under normal conditions, the gravity of the star pulling the elements inwards is enough to counter-act this force. Intuitively, we can say that larger stars will go through much faster and higher rates of fusion. This releases even more outwards pressure, until you get to a point when the star’s gravity is no longer strong enough to hold it together. Astronomers have established this limit at around 150 solar masses (150x more massive than our sun).