Have you ever wondered what the largest star in the universe is and why it holds such a title? To understand this, we must first explore the nature of stars and their fascinating journey from formation to their ultimate fate.
Our journey begins with Earth, not to learn anything specific, but to gain a sense of scale. The smallest objects with star-like properties are large gas giants, such as Jupiter, the most massive planet in our solar system. Jupiter is eleven times larger and 317 times more massive than Earth, composed of similar elements as our Sun, but in much smaller quantities.
The transition towards stars begins with brown dwarfs, often referred to as failed stars. These celestial bodies have between 13 and 90 times the mass of Jupiter. Even if we combined 90 Jupiters, it wouldn’t be enough to create a star. Brown dwarfs are dense, with certain nuclear fusion reactions occurring slowly, causing them to glow faintly. However, they don’t fit neatly into any category.
Once a gas ball surpasses a certain mass threshold, its core becomes hot and dense enough to ignite. Hydrogen fuses into helium, releasing tremendous energy, marking the birth of a main sequence star. The more massive the star, the hotter and brighter it burns, but its lifespan is shorter.
The smallest real stars are red dwarfs, barely massive enough to fuse hydrogen into helium. They burn their fuel slowly, lasting up to ten trillion years. In contrast, stars like our Sun, which dominates our solar system, burn hotter and brighter, reducing their lifespan to about 10 billion years.
As stars exhaust their hydrogen, they enter a giant phase, swelling to enormous sizes. For example, Gacrux, only 30% more massive than the Sun, has expanded to 84 times its radius. Eventually, our Sun will also become a red giant, expanding to 200 times its current size.
Hypergiants represent the largest stars in the universe. These stars have vast surfaces that radiate immense amounts of light. Pistol Star, a blue hypergiant, is 25 solar masses but 300 times the radius of the Sun. Even larger are yellow hypergiants like Rho Cassiopeiae, which is 500 times the radius of the Sun and 500,000 times brighter.
Among the largest stars known is Stephenson 2-18, a red hypergiant. Initially a main sequence star with a mass several times that of the Sun, it has likely lost about half its mass. Its estimated size is 2150 solar radii, shining with almost half a million times the power of the Sun. To put this in perspective, if placed in our solar system, it would extend beyond Saturn’s orbit.
As Stephenson 2-18 evolves, it will shed more mass, eventually exploding in a core-collapse supernova, contributing its gas back to the galaxy. This gas will form new stars, continuing the cycle of stellar birth and death.
The universe is vast, filled with objects of unimaginable size. To explore this further, you can use the “Universe In A Nutshell” app, created in collaboration with Tim Urban from Wait But Why. This app allows you to travel from the smallest particles to the largest stars and galaxies, marveling at the scale of the observable universe.
Download the app from your app store for an ad-free experience with no in-app purchases. Your feedback is valuable as we continue to improve and create more digital experiences. Thank you for supporting our projects and exploring the wonders of the universe with us!
Using everyday objects like fruits, balls, and marbles, create a scale model of our solar system. This will help you understand the relative sizes of planets and stars. Compare these objects to the sizes of stars mentioned in the article, such as red dwarfs and hypergiants.
Draw a comic strip that illustrates the lifecycle of a star, from its formation as a gas giant to its potential end as a supernova. Include stages like brown dwarfs, main sequence stars, and hypergiants, using the information from the article to guide your story.
Choose a star mentioned in the article, such as Stephenson 2-18 or the Pistol Star, and research more about it. Prepare a short presentation or poster that includes its characteristics, size, and significance in the universe.
Download the “Universe In A Nutshell” app and explore the scale of the universe. Write a reflection on your experience, noting any surprising facts or insights about the size of stars and other celestial bodies.
Create a chart that classifies different types of stars based on their size, brightness, and lifespan. Use the article to help categorize stars like red dwarfs, main sequence stars, giants, and hypergiants, and include a brief description of each type.
Star – A massive, luminous sphere of plasma held together by gravity, often visible in the night sky. – Example sentence: The Sun is the closest star to Earth and provides us with light and warmth.
Universe – All of space and everything in it, including stars, planets, galaxies, and all forms of matter and energy. – Example sentence: Scientists use powerful telescopes to explore the vast universe and discover new galaxies.
Hydrogen – The lightest and most abundant chemical element in the universe, often found in stars and gas clouds. – Example sentence: Hydrogen is the primary fuel for stars, allowing them to shine brightly for billions of years.
Helium – A chemical element that is the second lightest and second most abundant in the universe, often produced in stars. – Example sentence: As stars burn hydrogen, they create helium through a process called nuclear fusion.
Mass – The amount of matter in an object, which affects its gravitational pull. – Example sentence: The mass of a planet determines how strong its gravity is, affecting how much you would weigh there.
Giant – A term used to describe a very large star that is much bigger than the Sun. – Example sentence: A red giant is a type of star that has expanded and cooled, becoming much larger than it was originally.
Solar – Relating to the Sun or derived from the Sun’s energy. – Example sentence: Solar panels capture sunlight and convert it into electricity to power homes and devices.
Light – Electromagnetic radiation that is visible to the human eye, allowing us to see the world around us. – Example sentence: Light from distant stars takes many years to reach Earth, allowing us to see them in the night sky.
Gas – A state of matter consisting of particles that have neither a defined volume nor shape, often found in stars and planets. – Example sentence: The atmosphere of Jupiter is mostly made up of hydrogen and helium gas.
Galaxy – A large system of stars, gas, dust, and dark matter bound together by gravity. – Example sentence: The Milky Way is the galaxy that contains our solar system, along with billions of other stars.
