Life Cycle of a Massive Star
Stars are easily one of the most exciting things in all of space, possibly only second to one of the most intriguing and exciting phenomena in all of Astronomy; black holes!
As we’ve been reviewing in this series about the life cycle of stars, no matter their size, shape, location or astronomical genetics; they have very similar lives. It’s their deaths that differentiate them from one another.
In the life cycle of average stars (ones roughly the same size as our Sun), their lives end in an infinity of emptiness as a black dwarf.
In the life cycle of a big star (categorized as a star roughly 1.5 – 3 times the size of the Sun), their lives end in a much more exciting finale than average stars. Big stars end with a supernova which result in a Neutron star. One of the densest objects known.
As we’ve seen time and time again, in Astronomy, size matters. The life cycle of stars is no different and what we’re going to find out with the life cycle of a massive star; their size leads to one of the most exciting event in all of the Universe; black holes.
While average stars are less than or equal to 1.5 times the size of our Solar System’s star, and big stars are 1.5 – 3 times the size of our Sun; massive stars are in a league of their own, a floor and no ceiling.
Massive stars are no smaller than 3 times the mass of our Solar System’s star, the Sun and can be as much as 1,700 times or more the size of our Sun. To learn more about the biggest star in the Universe, check out this article and scroll to the bottom to see the chart with the largest known stars in the Universe.
UY Scuti is the most massive star and it’s 1,708 times the size of our Sun, 9.500 light years away and has a circumference of roughly 4,712,388,980 miles. As compared to our Sun which has a circumference of about 2,713,406 miles. LOL, just a little guy.
The Life Cycle of a Massive Star – Birth:
The birth of a massive star is really no different from any other star. It begins its life in a Giant Molecular Cloud, also referred to as a Nebula. These giant molecular clouds are mega collections of gas and dust, just floating around space doing their thing.
What are giant molecular clouds? Well, they are the birth places for stars, a stellar nursery. They’re essential to the creation of stars, solar systems, planets and possibly; life. They’re made of lots of little atoms which eventually turn themselves into hydrogen, which get to be so massive that they actually get too big and collapse. Boom!
Giant molecular clouds can be 100 to even 600 light years in width. That’s freakin’ huge! It’s basically equivalent to between 587,862,537,318,360 to 3,527,175,223,910,164 miles, in diameter. So, as the outer layers collapse on the inner layers of a giant molecular cloud, it begins the creation of what’s known as a protostar. Protostars are like little infant stars, they later grow up and become main sequence stars and eventually they die – more on that later.
So no matter what size a star is, their life cycle is basically the same at birth. They come from giant molecular clouds collapsing on itself and creating little baby stars, so cute!
The Life Cycle of a Massive Star – The Middle Years:
As a star matures and goes through its awkward stages of adolescence, it spends a great deal of time doing one thing; nuclear fusion. Stars fuse elements in the main sequence phase of their lives, which is estimated to be roughly 90% of their existence.
Nuclear fusion is the process a star goes through when it’s converting hydrogen into helium. You’re probably already very familiar with nuclear fusion, so we won’t go too deep into the details here.
Since you’ve heard E=mc2 a billion times, you know that (E) energy is equal to the (M) mass of an object(s) multiplied by the (C) speed of light in a vacuum, to the second power.
Give Me a Quick and Simple Example of Nuclear Fusion:
Nuclear fusion for a star is pretty simple, but totally complicated.
Here’s a quick and simple rundown. Stars have hydrogen atoms, lots of them and these atoms are flying all around in its core. Eventually, these atoms collide with one another at super fast speeds and fuse together (yeah, this is the part where you’re like, this is nuclear fusion taking place, right now).
These two larger and lighter elements (hydrogen) get super smashed into a new, single and heavier element; helium. A star will spend a great deal of time doing this process and eventually the balance of hydrogen and helium shift.
At the point where there is enough helium, this element starts to fuse together in the core of a star and when it smashes and collides two helium atoms with one another; it creates an even smaller and heavier element; carbon!
So What Does Nuclear Fusion Actually Do?
Nuclear fusion is what creates the heat and brightness of a star and helps us in determining how old and how big stars actually are. To learn more about the types of stars in Astronomy and the Hertzsprung–Russell diagram, check out this article.
Nuclear fusion is such an important component to the life cycle of a massive star, it helps us understand how much fuel a star has and how long its estimated life will be.
How Old Can Stars Actually Live?
For smaller and average sized stars (less than or equal to 1.5 times the size of our Sun), they can get to be as old as 2,000,000,000,000 and 2,000,000,000 years.
Think about that, the Universe is only 13.8 billion years old, so in theory some of the oldest stars can still be alive today from when the Universe was born.
Big stars that are 1.5 to 3 times the size of our Sun can live to be as old as 2,000,000,000 and 200,000,000 years old. Which is still pretty incredible; old enough to remember the Dinosaurs, if that’s even possible.
For massive stars between the size of 3 to 60 times the size of our Sun, they generally live between 200,000,000 and 3,400,000 years.
The Life Cycle of a Massive Star – The Golden Years:
At this point in the life cycle of a massive star, it’s been fusing hydrogen into helium for a long time. In fact, for millions of years this star has had so much fuel, hydrogen atoms, that it was able to spend all day, every minute smashing them together and creating new elements and energy.
Because of the increasing weight of the star’s core from fusing lighter elements into heavier ones, it’s starting to die. Even though this sounds sad, it’s actually the start of a very exciting and awesome process which ends in probably the most awesome event in all of astronomy; a black hole.
The Red Supergiant Phase:
As the star gets older and runs out of hydrogen and is mostly composed of helium, the star’s core gets heavier and begins to shrink. As the core shrinks, it gets hotter and hotter – denser and denser.
Eventually, the core is hot and dense enough to fuse the helium into carbon, the next heavy element in the chain of nuclear fusion and in the life cycle of a massive star.
Eventually, the massive star’s core will get so hot and dense that it’ll fuse the carbon into smaller and denser elements; neon, oxygen and silicon.
Think of this phase in the life cycle of a massive star like an onion. Each of the different layers of the “onion”, or star in this example, are fusing lighter elements into smaller, denser elements.
In the end, our big, bright and beautiful massive star will have fused its hydrogen ⇒ helium, helium ⇒ carbon, its carbon ⇒ neon, the neon ⇒ oxygen, all the oxygen ⇒ silicon and eventually we’re left with iron at the core.
Since we all know that the nuclei of iron are too heavy to fuse with one another, fusion after iron doesn’t produce a net effect of energy, therefore there’s nothing left to do expect move on to the next phase in the life cycle of a massive star.
The Supernova Phase
The next phase in the life cycle of a massive star is when all of the elements in the massive star’s core have been fused to the point where only iron is left. This is when a star has become so large it can no longer support itself.
At this point, in a single instant, a massive gravitational collapse takes place when the massive star’s core is nearing 100 billion degrees and its electrons get smashed into its protons, creating neutrons, gamma rays and neutrinos. Boom, collapse, it goes supernova!
When a star goes supernova it expels the brightness of over 100 million (our Solar System’s star) Suns. This event creates so much light, people on Earth have reported seeing them with just a naked eye.
As the supernova explosion is taking place, its burst of power spreads all of the star’s outer layer (full of elements) out into the voids of the Universe. After this awesome and exciting event takes place, it leads us to the next phase in the life cycle of a massive star; a black hole.
The Black Hole Phase:
Now that our massive star has fused all of its elements into iron (fusion can no longer occur), it ha become so damn big it collapsed on itself, causing a supernova.
Stars that are considered massive aren’t done with their life cycle just yet. There is one last event that needs to take place and it creates one of the most amazing and mysterious objects in all of Astronomy; black holes.
Due to the size of the massive star and the energy and power released from its supernova, a massive star will eventually become a black hole in the final phase of its life cycle.
The field of Astronomy and Science continues to investigate and learn about black holes. Today, there’s enough known to make you wonder and imagine all of the mysteries that these unique objects hold.
A black hole is an object which has such a strong gravitational effect that literally nothing can escape from inside it.
To put this into perspective, imagine you dig a hole in your backyard. Let’s say that it’s of decent size; a few feet wide and maybe 10 feet deep or so. If you were to take a bouncy ball, hold it directly over the hole and drop it straight down, it would hit the bottom and bounce back up. Gravity on Earth wouldn’t be strong enough to keep it from “escaping” and returning to you (above the hole).
Now imagine a second experiment, you set a piece of paper on fire and you drop it down in the hole. As the piece of paper, which is now burning and illuminating light, drops down, deeper and deeper into the hole you’ve dug, you’d still be able to see the light illuminating from the paper burning.
Now, let’s imagine the hole you dug was a black hole, the gravity would be much, much (and many more much’s) stronger than the gravity here on the surface of the Earth.
In your first experiment, the black hole’s gravity would have been so strong that the bouncy ball never would have even bounced. It would just be gone. And actually, if you were standing over the black hole, you’d be gone too, but that’s not the point.
In your second experiment, the gravity of the black hole would have been so strong, that the piece of paper you set on fire would have been gone and not observable the instant it passed the black hole’s event horizon. At the point of a black hole’s event horizon, there’s no turning back. Once an object enters this point, it’s gone. Nothing, not even light, can escape the gravitational power of its pull.
What Happens to Black Holes?
Black holes just chill out and consume things, possibly forever. Anything close enough to a black hole’s gravitational pull or in its path gets sucked up into the black hole’s singularity and increases the mass of the black hole.
Black holes devour anything in its proximity; stars, planets, smaller astronomical objects and yeah, even other black holes.
When black holes consume enough and get large enough, they eventually become what’s known as supermassive black holes. These supermassive black holes can be millions of times the size and mass of our Sun.
Most Astronomers believe that supermassive black holes are found at the center of most galaxies. In fact, our galaxy, the Milky Way has its own supermassive black hole; Sagittarius A*. It’s huge, basically 4.3 million times the mass of our Sun. Thank goodness we’re not there, or we’d be goners.
Well, that’s the last phase in the life cycle of a massive star. There’s likely no better way to die, than to become a black hole.