When you head out the door to snap fantastic astrophotos, you’ve surely noticed that not all stars have the same color. Scientists have grouped stars based on size and color to help categorize the roughly 200 billion stars in our galaxy alone. Today’s article looks at blue giant stars and what makes them unique.
What Is a Star?
A star at its simplest is a giant ball of hydrogen and helium held together by its own gravity. These celestial objects are in the constant process of converting hydrogen to helium through nuclear fusion. This results in the non-stop emission of heat and light out into the cosmos.
A Star’s Color Tells Temperature
The known stars in our universe fall into one of seven different types, based solely on color and temperature. We often think of red or orange when we think of heat, but when it comes to stars, these are the coolest colors.
On the contrary, blue stars are the hottest in the spectrum. Where a star like our Sun has a surface temperature of around 5,700 Kelvin, blue stars hang out in the 28,000 – 50,000 Kelvin range.
Giant Refers to Physical Size
During the long period of time that stars convert hydrogen to helium, they are known as main sequence stars. Once a star consumes all its hydrogen, the core superheats and pushes its surface layers far out into space. The star has now become a giant.
It should come as no surprise that a giant star is significantly larger in size than when it was in the main sequence. As they push outward, giant stars can become 5 to 10 times larger than they once were. The largest blue giants are often referred to as supergiant stars.
Surprisingly, blue giants don’t swell up nearly as big as their red cousins do. It’s not uncommon for a red giant to inflate to 100 times its previous size, with some reaching 1000 times its previous diameter!
To stay alive, giant stars begin to fuse helium into other elements to maintain heat and light. Most giant stars cool off considerably and become red, but blue stars hold onto enough heat to keep their color.
Giant Can Also Mean Mass
An object’s size doesn’t necessarily translate to its mass or how heavy it is. Black holes are some of the smallest things known to humanity but are so massive that even light cannot escape.
Even if not as big as their red giant counterparts, blue giants do find themselves quite massive. The smallest blue stars are at least three times the mass of the Sun, whereas the largest on record is 300 times as massive as our star.
These Stars Are Very Luminous
In addition to being very hot, blue giant stars are also very bright. It’s not apparent to us from Earth, but blue giants make up the most luminous stars in the universe. The current record holder, R136a1, is about 9 million times more luminous than our Sun. This single star generates more energy in a few seconds than our Sun does in a year!
They Are Quite Rare
Blue stars make up a tiny percentage of the stars we can see in our Milky Way galaxy. It takes a lot of energy to reach such a level, and most stars simply don’t get there. We’re just starting to look beyond our galaxy, but this pattern will likely continue in others as well.
They Don’t Live Very Long
If a star has become a blue giant, it’s already reached at least the middle age of its lifespan. Because these stars burn through hydrogen so quickly, it doesn’t take long (from a stellar standpoint) to get there.
Our Sun is approximately 4.5 billion years old, about halfway through its life. Red stars burn fuel so slowly that they have the potential to last trillions of years. That’s 100 times longer than our Sun.
A blue star survives on average only 15 to 20 million years. They go giant after eight million years after having already burned through all the hydrogen it has. Blue stars die out 1000 times faster than even a yellow star like our Sun, let alone a red star!
They Don’t Have Planets
From what we’re able to understand, planets take a few billion years to form on their own. When a blue star only has 20 million years at best to live, there’s simply not enough time for a planet to come to be.
These fiery blue suns also generate powerful solar winds, making planetary formation that much harder. If there is somehow a blue star out there with a planet, we’ve yet to find it.
End of Life
At the end of a blue giant star’s life, things change very quickly. Because these stars are so massive, they collapse in on themselves in only a few short moments. This collapse leads to an enormous explosion called a supernova that throws stellar debris out into space.
These events are infrequent, and it’s estimated only a few happen every century in our galaxy. The end result of a supernova is often a cosmic cloud called a nebula that can potentially be the birthplace of new stars. The largest supernovae have the potential to turn into black holes.
Notable Blue Giants in the Milky Way Galaxy
There aren’t many blue giant stars that we’re aware of, but a few notable mentions live in our galaxy.
- Rigel in the constellation Orion
- Alnilam in the constellation Orion
- Zosma in the constellation Leo
- Naos in the constellation Puppis
- Alcyone in the constellation Taurus
- Spica in the constellation Virgo
Blue giant stars are true rarities in our galaxy and likely also in the rest of the universe. Their intense energy consumption leads to incredible temperatures and luminosities that are off the charts. Sadly, these stars only manage to survive 15 to 20 million years before giving their last.
Even though most blue giants are hundreds of light-years away, they provide enough light to make epic astrophotos. After all, what would Orion be without his knee or one of the stars on his belt?