The Largest Star in the Universe – Size Comparison

Summary

This script delves into the cosmic scale of stars, from the smallest gas giants to the largest hypergiants. It explains the progression from brown dwarfs to main sequence stars, highlighting the differences in size, brightness, and lifespan based on mass. The script introduces the most massive known star, R136a1, and the largest, Stephenson 2-18, illustrating the rarity and short lives of such celestial behemoths. It concludes with the cyclical nature of star birth, death, and the formation of new stars, emphasizing the universe's vastness and the ongoing cosmic dance.

Takeaways

• 🌌 The universe contains the largest star known as R136a1, which has 315 solar masses and is 9 million times brighter than the Sun.
• 🔥 Stars are massive celestial bodies that undergo nuclear fusion in their cores, converting hydrogen into helium and releasing energy.
• 🌑 Sub-brown dwarfs, like Jupiter, are the smallest objects with star-like properties but lack the mass to ignite nuclear fusion.
• 🌟 Brown dwarfs are sometimes called 'failed stars' and have a mass between 13 and 90 times that of Jupiter, capable of slow nuclear fusion.
• ✨ Main sequence stars are the most common type of star, including our Sun, and they fuse hydrogen into helium in their cores.
• 🌕 Red dwarfs are the smallest and most abundant main sequence stars, with a long lifespan due to their slow fuel consumption.
• 🌞 The Sun is a G-type main sequence star, larger and brighter than red dwarfs, with a lifespan of about 10 billion years.
• 🌌 Sirius, the brightest star in the night sky, is twice as massive as the Sun and shines 25 times brighter, with a shorter lifespan.
• 🌀 Stars with around 10 solar masses have surface temperatures near 25,000°C and are extremely luminous but short-lived.
• 💥 The most massive stars, like R136a1, are rare and lose a significant amount of material through stellar winds due to their extreme properties.
• 🌀 Red giants are a phase in a star's life when it exhausts hydrogen in its core, leading to a significant increase in size.
• 🌀 Hypergiants are the largest and rarest type of stars, with immense surface areas and powerful stellar winds that can blow themselves apart.
• 🌌 The largest known star, Stephenson 2-18, is estimated to be around 2150 times the size of the Sun and shines with almost half a million times the power of the Sun.

Q & A

What is the largest star in the universe currently known?

The largest star currently thought to be among the largest we've found is Stephenson 2-18, which is estimated to be around 2150 times the size of the Sun.

Why are stars like R136a1 rare and short-lived?

Stars like R136a1 are rare because they form through the merger of several high mass stars in dense star-forming regions. They are short-lived because they burn their core hydrogen in only a few million years.

What is the difference between a brown dwarf and a main sequence star?

A brown dwarf is a failed star that has between 13 and 90 times the mass of Jupiter and can undergo slow nuclear fusion reactions, but it doesn't ignite like a main sequence star. Main sequence stars have enough mass to ignite hydrogen into helium in their cores, releasing tremendous amounts of energy.

What happens to a star when it exhausts hydrogen in its core?

When a main sequence star exhausts the hydrogen in its core, it contracts, making it hotter and denser, leading to a faster fusion process that pushes back against gravity and causes the outer layers to swell, entering a giant phase.

How do hypergiants differ from other types of stars?

Hypergiants are the giant phase of the most massive stars in the universe. They have an enormous surface area that can radiate an insane amount of light and are so large that they are essentially blowing themselves apart due to the weak gravity at the surface.

What is the role of the stellar wind in supermassive stars?

The stellar wind in supermassive stars is responsible for losing a significant amount of material from the star every second. For example, R136a1 loses 321 thousand billion tons of material through its stellar wind every second.

Why are red dwarfs the most abundant type of star in the universe?

Red dwarfs are the most abundant type of star in the universe because they burn their fuel very slowly, which allows them to last up to ten trillion years, a thousand times the current age of the universe.

How does the mass of a star affect its brightness and lifespan?

The more massive a main sequence star is, the hotter and brighter it burns, but the shorter its life is. For instance, Sirius, with 2 solar masses, shines 25 times brighter than the Sun but has a lifespan reduced to 2.5 billion years.

What is the significance of the Sun's mass in the solar system?

The Sun is significant in the solar system as it makes up 99.86% of all its mass, dominating and influencing the dynamics and environment of the entire system.

How does the size of a star relate to its life cycle?

The size of a star is directly related to its life cycle. Larger stars burn hotter and brighter, leading to shorter lifespans. Conversely, smaller stars like red dwarfs have longer lifespans due to their slower fuel consumption.

What is the Universe In A Nutshell app, and how does it relate to the script?

The Universe In A Nutshell app is a tool created by Kurzgesagt in collaboration with Tim Urban, which allows users to explore the scale of the universe, from the smallest particles to the largest stars and galaxies, inspired by the concepts discussed in the script.

Outlines

00:00

🌌 Introduction to Stars and Their Scales

This paragraph introduces the topic of stars, questioning what the largest star in the universe is and why it is so large. It starts by giving a sense of scale with Earth and then discusses the properties of gas giants and sub-brown dwarfs, like Jupiter. The script explains the transition to stars with brown dwarfs, which are considered 'failed stars.' It details the process of nuclear fusion in main sequence stars and how their mass affects their brightness and lifespan. The paragraph also touches on the different stages of a star's life, from red dwarfs, which are the smallest and most abundant, to stars like our Sun and even larger stars like Sirius and Beta Centauri, which have shorter lifespans due to their higher mass and brightness.

05:01

🌠 The Extremes of Stellar Mass and Size

This paragraph delves into the upper limits of stellar mass and size, focusing on the most massive known star, R136a1, which has 315 solar masses and is nearly 9 million times brighter than the Sun, yet only about 30 times the Sun's size. It discusses the rarity and short lifespan of such stars, which are believed to form through the merger of several high-mass stars. The script also explores the process of red giants, which are main sequence stars that have exhausted their core hydrogen and begin to swell due to increased fusion in their cores. Hypergiants are introduced as the largest stars, with Pistol Star and Rho Cassiopeiae being highlighted for their immense size and brightness. The paragraph concludes by discussing the current understanding of the largest stars, such as Stephenson 2-18, and the cyclical nature of star birth and death in the universe.

10:03

📲 Universe Exploration Through Kurzgesagt's App

The final paragraph shifts focus from the stars to an invitation to explore the universe using Kurzgesagt's first app, 'Universe In A Nutshell,' created in collaboration with Tim Urban of Wait But Why. The app allows users to journey through the observable universe, from the smallest particles to the largest celestial bodies. It provides information about each object and emphasizes the sheer scale of the universe. The paragraph also mentions the app's availability in app stores, its lack of in-app purchases or ads, and the creators' desire for feedback to improve the app. The script ends by acknowledging the support of viewers and the funding of Kurzgesagt projects, encouraging viewers to download the app and leave a positive review.

Keywords

💡Star

A star is a massive, luminous sphere of plasma held together by its own gravity. In the context of the video, stars are the primary focus, representing celestial bodies that undergo nuclear fusion to emit light and heat. The script discusses various types of stars, their sizes, and their lifecycles, emphasizing the vastness and variety within the universe.

💡Brown Dwarf

A brown dwarf is a celestial object that is larger than a planet but not massive enough to sustain the nuclear fusion of hydrogen in its core, which is the process that powers stars. The script introduces brown dwarfs as 'failed stars' that are a transition between planets and stars, with masses between 13 and 90 times that of Jupiter.

💡Main Sequence Star

Main sequence stars are stars, like our Sun, that are in the stable phase of their life cycle where they are fusing hydrogen into helium in their cores. The video explains that the mass of a main sequence star determines its size, temperature, brightness, and lifespan, with more massive stars burning hotter and shorter lives.

💡Red Dwarf

Red dwarfs are the smallest and most abundant type of main sequence stars. They have a mass of about 100 times that of Jupiter and are characterized by their long lifespan due to slow fuel consumption. The script mentions Barnard's Star as an example of a red dwarf, which is too dim to be seen without a telescope.

💡Sirius

Sirius is the brightest star in the night sky and is used in the script as an example of a main sequence star with a mass of about 2 solar masses. It has a higher surface temperature and shines 25 times brighter than the Sun, which also shortens its lifespan to 2.5 billion years.

💡Beta Centauri

Beta Centauri is a star system mentioned in the script that contains two stars, each with a mass close to 10 times that of the Sun. These stars are extremely bright and powerful, shining with about 20,000 times the power of the Sun, but they have a much shorter lifespan of about 20 million years.

💡R136a1

R136a1 is the most massive star known to humanity, with 315 solar masses and nearly 9 million times the brightness of the Sun. The script describes it as an extreme star that is barely held together by gravity and loses a significant amount of material through its stellar wind every second.

💡Hypergiant

Hypergiants are a class of stars that represent the giant phase of the most massive stars in the universe. They have enormous surface areas and radiate an immense amount of light. The script discusses two types of hypergiants: blue and yellow, with the latter being exemplified by Rho Cassiopeiae, which is 500,000 times brighter than the Sun.

💡Red Giant

A red giant is a stage in the life cycle of a star that has exhausted the hydrogen in its core. The core contracts, leading to a hotter and denser environment that causes the outer layers to swell. The script uses Gacrux and the future state of the Sun as examples of red giants, which can become hundreds of thousands of times their original size.

💡Stephenson 2-18

Stephenson 2-18 is mentioned in the script as one of the largest stars currently known, possibly a red hypergiant. It is estimated to be around 2150 times the size of the Sun and shines with almost half a million times the power of the Sun. This star exemplifies the extreme scales of celestial objects in the universe.

💡Stellar Wind

Stellar wind refers to the continuous outflow of gas from the outer atmosphere of a star. In the context of the script, it is particularly relevant for massive stars like R136a1, which loses a significant amount of material through its stellar wind every second, demonstrating the dynamic and volatile nature of such stars.

Highlights

The largest star in the universe is R136a1, with 315 solar masses and nearly 9 million times brighter than the Sun.

Stars are celestial bodies that undergo nuclear fusion in their cores, converting hydrogen into helium and releasing energy.

Sub-brown dwarfs, like Jupiter, are large gas giants with star-like properties but lack the mass to ignite nuclear fusion.

Brown dwarfs, with 13 to 90 times the mass of Jupiter, are failed stars that can undergo slow nuclear fusion reactions.

Main sequence stars range from red dwarfs, the smallest and longest-lived stars, to massive stars like R136a1 with short lifespans.

Red dwarfs are the most abundant stars in the universe due to their slow fuel consumption, lasting up to ten trillion years.

The Sun, a G-type main sequence star, has a lifespan of about 10 billion years and is 99.86% of the solar system's mass.

Sirius, the brightest star in the night sky, is twice as massive as the Sun and shines 25 times brighter.

Beta Centauri contains two stars, each with 20,000 times the power of the Sun, but with a lifespan of only 20 million years.

Hypergiants are the largest stars, with enormous surface areas and intense radiation, often blowing themselves apart.

Pistol Star, a blue hypergiant, is 25 solar masses with a radius 300 times that of the Sun.

Rho Cassiopeiae, a yellow hypergiant, is 40 solar masses and 500,000 times brighter than the Sun.

Stephenson 2-18 is among the largest known stars, estimated at 2150 times the size of the Sun and half a million times brighter.

Stars go through cycles of birth, death, and rebirth, contributing to the ongoing formation of new stars in the universe.

Kurzgesagt's Universe In A Nutshell app allows users to explore the scale of the universe from the smallest to the largest objects.

Transcripts

What is the largest star in the universe

and why is it that large?

And what are stars anyway?

Things That Would Like To Be Stars

We begin our journey with Earth.

Not to learn anything,

just to get a vague sense of scale.

The smallest things that have some star-like properties

are large gas giants, or sub-brown dwarfs.

Like Jupiter, the most massive planet in the solar system.

Eleven times larger and 317 times more massive than Earth,

and more or less, made of the same stuff as our Sun.

Just much, much less of it.

The transition towards stars begins with brown dwarfs,

failed stars, that are a huge disappointment to their moms.

They have between 13 and 90 times the mass of Jupiter.

So even if we took 90 Jupiters and threw them at each other,

although fun to watch,

it wouldn't be enough to create a star.

Interestingly, adding lots of mass to a brown dwarf

doesn't make it much bigger,

just its insides denser.

This increases the pressure in the core enough

to make certain nuclear fusion reactions happen slowly,

and the object glow a little.

So brown dwarfs are a sort of glowy gas giant,

that don't fit into any category very well.

But we want to talk about stars,

not failed wannabe stars, so let's move on.

Main Sequence Stars

Once large gas balls pass a certain mass threshold,

their cores become hot and dense enough to ignite.

Hydrogen is fused to helium in their cores,

releasing tremendous amounts of energy.

Stars that do that are called main sequence stars.

The more massive a main sequence star is,

the hotter and brighter it burns,

and the shorter its life is.

Once the hydrogen-burning phase is over,

stars grow up to hundreds of thousands of times their original size.

But these giant phases only last for a fraction of their lifespan.

So we'll be comparing stars at drastically

different stages in their lives.

This doesn't make them less impressive,

but maybe it's good to keep in mind that we'll be

comparing babies to adults.

Now back to the beginning,

the smallest real stars are red dwarfs.

About 100 times the mass of Jupiter;

barely massive enough to fuse hydrogen to helium.

Because they are not very massive

they are small, not very hot, and shine pretty dimly.

They are the only stars in the main sequence that

don't grow once they die

but sort of fizzle out.

Red dwarfs are by far the most

abundant type in the universe,

because they burn their fuel so slowly,

it lasts them up to ten trillion years -

a thousand times the current age of the universe.

For example, one of the closest stars to Earth is a red dwarf star,

Barnard's Star,

but it shines too dimly to be seen without a telescope.

We made a whole video on red dwarfs if you want to learn more.

The next stage are stars like our Sun.

To say the Sun dominates the solar

system is not doing it justice

since it makes up 99.86% of all its mass.

It burns far hotter and brighter than red dwarfs,

which reduces its lifetime to about 10 billion years.

The Sun is 7 times more massive than Barnard's Star,

but that makes it nearly 300 times brighter with

twice its surface temperature.

Let's go bigger!

Small changes in mass produce enormous

changes in a main sequence star's brightness.

The brightest star in the night sky, Sirius, is 2 solar masses

with a radius 1.7 times that of the Sun,

but its surface is nearly 10,000°C,

making it shine 25 times brighter.

Burning THAT hot reduces its total

lifespan by 4 times to 2.5 billion years.

Stars close to 10 times the mass of our sun

have surface temperatures near 25,000°C.

Beta Centauri contains two of these massive stars,

each shining with about 20,000 times the power of the Sun.

That's a lot of power coming from

something only 13 times larger,

but they'll only burn for about 20 million years.

Entire generations of the blue stars die in the time

it takes for the Sun to orbit the galaxy once.

So is this the formula?

The more massive, the larger the star.

The most massive star that we know is R136a1.

It has 315 solar masses

and is nearly 9 million times brighter than the Sun.

And yet, despite its tremendous mass and power,

it's barely 30 times the size of the Sun!

The star is so extreme and barely held together by gravity

that is loses 321 thousand billion tons

of material through its stellar wind

every single second.

Stars of this sort are extremely rare because they

break the rules of star formation a tiny bit.

When supermassive stars are born

they burn extremely hot and bright

and this blows away any extra gas

that could make them more massive.

So the mass limit for such a star is

around 150 times the Sun.

Stars like R136a1 are probably formed through

the merger of several high mass stars

in dense star-forming regions

and burn their core hydrogen in only a few million years.

So this means they are rare and short lived.

From here the trick to going bigger isn't adding more mass.

To make the biggest stars we have

to kill them.

Red Giants

When main sequence stars begin to

exhaust the hydrogen in their core

it contracts making it hotter and denser.

This leads to hotter and faster fusion

which pushes back against gravity

and makes the outer layers swell in a giant phase.

And these stars become truly giant indeed.

For example, Gacrux.

Only 30% more massive than the Sun,

it has swollen to about 84 times its radius.

Still, when the Sun enters the last stage of its life,

it will swell and become even bigger;

200 times its current radius!

In this final phase of its life

it will swallow the inner planets.

And if you think THAT'S impressive

let's finally introduce the largest stars in the universe:

Hypergiants

Hypergiants are the giant phase of the most massive stars in the universe.

They have an enormous surface area

that can radiate an insane amount of light.

Being so large they're basically blowing themselves apart

as gravity at the surface is too weak to hold on to the hot mass

which is lifted away in powerful stellar winds.

Pistol Star is 25 solar masses

but 300 times the radius of the sun;

a blue hypergiant aptly named for its energetic blue starlight.

It's hard to say exactly how long Pistol Star will live

but probably just a few million years.

Even larger than the blue hypergiants

are the yellow hypergiants.

The most well studied is Rho Cassiopeiae;

a star so bright it can be seen with the naked eye although

it's thousands of lightyears from Earth.

At 40 solar masses,

this star is around 500 times the radius of the Sun,

and 500,000 times brighter.

If the Earth were as close to Rho Cassiopeiae as it is to the Sun

it'd be inside it and you would be very dead.

Yellow hypergiants are very rare though.

Only 15 are known.

This means they're likely just a short-lived intermediate state

as a star grows or shrinks between other phases of hypergiantness.

With red hypergiants we reach the largest stars known to us.

Probably the largest stars even possible!

So who's the winner of this insane contest?

Well the truth is we don't know.

Red hypergiants are extremely bright and far away

which means the even tiny uncertainties in our measurements

can give us a huge margin of error for their size.

Worse still are solar system sized behemoths

that are blowing themselves apart

which makes them harder to measure.

As we do more science and our instruments improve

whatever the largest star is will change.

The star that is currently thought to be among the largest we've found

is Stephenson 2-18.

It was probably as a main sequence star a few tens

of times the mass of the sun

and has likely lost about half its mass by now.

While typical red hypergiants are 1500 times the size of the Sun,

the largest rough estimate places Stephenson 2-18 at 2150 solar radii,

and shining with almost half a million times the power of the Sun!

By comparison the Sun seems like a grain of dust.

Our brains don't really have a way of grasping this kind of scale.

Even at lightspeed it would take you 8.7 hours to travel around it once.

The fastest plane on Earth would take around 500 years!

Dropped on the Sun it would fill Saturn's orbit!

As it evolves it would probably shed even more mass

and shrink down into another hotter hypergiant phase,

accumulate heavy elements in its core,

before finally exploding in a core collapse supernova,

giving its gas back to the galaxy.

This gas will then go on to form another generation

of stars of all sizes.

Starting the cycle of birth and death again

to light up our universe.

Let's make this journey again

but this time without the talking.

The universe is BIG.

There are many large things in it.

If you want to play a bit more with size stuff

we have good news!

We've crated our first app, Universe In A Nutshell,

together with Tim Urban, the brain behind Wait But Why.

You can seamlessly travel from the smallest things in existence,

past the coronavirus,

human cells and dinosaurs,

all the way to the largest stars and galaxies,

and marvel at the whole observable universe!

You can learn more about each object,

or simply enjoy the sheer scale of it all.

The app is inspired by the Scale Of The Universe website

by the Huang twins,

that we spent a lot of time with when it came out years ago,

and felt that it was finally time to create a

Wait But Why and Kurzgesagt version.

You can get it in your app store,

there are no in-app purchases, and no ads.

All future updates are included.

And since this is our first app

we'd love to hear your feedback

so we can improve it over time.

If this sounds good to you

download the Universe In A Nutshell app now

and leave us a 5-star review if you want to support it.

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So if you like the app we'll make more digital things in future.

Thank you for watching!