How do Stars Work?

Summary

This script explores the life cycle of stars, from birth in molecular clouds to death as red giants, supernovae, or black holes. It explains how stars, like our Sun, are crucial for life and how they evolve through stages like protostars and main sequence dwarfs. The script also touches on the potential limits of star size and the endless possibilities within the universe's countless stars.

Takeaways

• 🌟 Stars have fascinated humanity for centuries, shaping culture, religion, and scientific progress.
• 🔭 While only a few stars are visible to the naked eye, the universe contains an unimaginable number of them—hundreds of sextillions.
• ☀️ Stars, like our Sun, are massive spheres of plasma that produce energy through nuclear fusion, primarily turning hydrogen into helium.
• 🌌 Galaxies, including the Milky Way, contain billions of stars, with many stars forming in clusters or from molecular clouds of dust and gas.
• 💥 Stars go through life cycles, from formation in molecular clouds to becoming protostars, then maturing into main sequence stars powered by fusion.
• 🔥 Larger stars eventually expand into red giants or supergiants when their hydrogen is exhausted, and they can grow to massive sizes like UY Scuti, 1,700 times larger than the Sun.
• 🌠 Supernovae occur when massive stars implode, leading to a brilliant explosion, dispersing elements that form new stars and planetary systems.
• 🌀 Some collapsed stars form neutron stars or black holes, with extreme gravitational fields that warp space-time itself.
• 🧬 Many of the elements that make up planets and life, including Earth, are created in the nuclear reactions inside stars, meaning we are all made of stardust.
• 🌍 Our own Sun will eventually become a red giant in about 5.5 billion years, which will have significant impacts on our solar system, potentially engulfing Mercury and Venus.

Q & A

What is the significance of stars in shaping our culture, religion, and scientific progress?

Stars have been a source of fascination since mankind first comprehended our existence. They have shaped our culture, religion, and scientific progress by inspiring myths, legends, and scientific inquiry. Their presence in the night sky has been a constant reminder of the vastness of the universe and our place within it.

How many stars can be seen with the naked eye and how does this compare to the total number in the universe?

With the naked eye, one can see a handful of stars, but the universe contains more stars than one can imagine. The exact number is incomprehensible, but it's estimated that there are hundreds of sextillions of stars shining throughout galaxies.

What is the role of nuclear fusion in stars and how does it relate to our energy needs on Earth?

Nuclear fusion is the process that powers stars for the majority of their lives, turning hydrogen into helium at their core. This process releases energy that moves to the surface and emits as stellar radiation. On Earth, scientists are trying to recreate nuclear fusion to solve our energy demands because it has the potential to provide a nearly limitless, clean energy source.

What is the mass of our Sun and how is it used to measure other stars?

The mass of our Sun is approximately 1.989 times 10 to the 27 tons, which is characterized as one solar mass. This unit of measurement is used to assess the mass of other stars in comparison to our own Sun.

How many stars are estimated to be in the visible universe and in our own galaxy, the Milky Way?

There are estimated to be as many as 300 sextillion stars in the visible universe, with approximately two to four hundred billion of these stars lying within our own galaxy, the Milky Way.

What is the role of constellations in astronomy and how are they formed?

Constellations are groups of particularly bright, local, and luminous stars that are grouped into shapes resembling humans, objects, and animals. They are useful for mapping the positions of nearby stars in the night sky.

How does a star form and what are the four main stages of its life cycle?

Star formation begins with molecular clouds, which are clouds of dust and atoms. These clouds collapse into a dense core due to gravity, forming a protostar. The protostar then incubates, trapping more hydrogen and helium within the core. Once sufficiently developed, it begins to emit gas and forms a planetary system. The four main stages of a star's life cycle are the protostar phase, main sequence, red giant phase, and the final stage which could be a white dwarf, neutron star, or black hole, depending on the star's mass.

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

Stars are massive enough to sustain nuclear fusion of hydrogen in their cores, while brown dwarfs have a mass more comparable to Jupiter and are unable to do so. Instead, they can fuse lithium and are often found between the size of an extremely large gas giant planet and an extremely light mass star.

What happens to a star during the red giant phase and what is the significance of this phase?

During the red giant phase, a star exhausts its hydrogen fuel and begins to fuse helium into heavier elements. The outer layers expand and cool, increasing the star's size dramatically and giving it a red color. This phase is significant as it marks the transition from the star's main sequence life to its dying phase.

What is a supernova and how does it relate to the life cycle of a massive star?

A supernova is a brilliant explosion that occurs when a massive star's core collapses under its own gravity after it has exhausted its nuclear fuel. This explosion disperses the star's outer layers, leaving a remnant such as a neutron star or a black hole. Supernovae are among the brightest events in the universe and play a crucial role in distributing heavy elements throughout space, which are necessary for the formation of planets and life.

What is the theoretical upper limit for the size of stars and why?

Theoretically, there should be an upper limit to the size of stars due to the properties of the star-forming molecular clouds, which cannot exceed a certain mass. However, the exact limit is not definitively known, with some stars like the Pistol Star estimated to be around 200 solar masses. The largest known star, UY Scutyi, is about 1,700 times the diameter of the Sun, and there are predictions that cool supergiant stars could grow up to 2,600 times the Sun's size.

Outlines

00:00

🌟 The Importance and Vastness of Stars

05:01

💫 The Formation of Stars: From Gas Clouds to Fusion

10:02

☀️ The Main Sequence and Life Stages of Stars

15:04

🔥 The Future of Our Sun and the Fate of Massive Stars

20:05

🌌 Supernovae, Neutron Stars, and Black Holes

Keywords

💡Star

A star is a massive celestial body composed mostly of hydrogen and helium in plasma state, held together by its own gravity. In the context of the video, stars are the fundamental building blocks of the universe, radiating light and heat that can influence entire galaxies. They are the source of life on Earth, with the Sun being a prime example. The video discusses the life cycle of stars, from their formation in molecular clouds to their eventual death.

💡Nuclear Fusion

Nuclear fusion is the process by which atomic nuclei combine to form heavier elements, releasing vast amounts of energy in the process. The video explains that stars, including our Sun, generate their energy primarily through nuclear fusion, where hydrogen is converted into helium, powering the star for most of its life.

💡Solar System

A solar system is a group of celestial bodies, including planets, asteroids, comets, and a star, bound together by gravity. The video uses our solar system as a reference point, highlighting the Sun's dominance in mass and its role in sustaining life and shaping the system.

💡Galaxy

A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants, interstellar gas and dust, and dark matter. The Milky Way, mentioned in the video, is an example of a galaxy that contains billions of stars, including our Sun. Galaxies are crucial in understanding star formation and distribution in the universe.

💡Constellation

A constellation is a group of stars that form a recognizable pattern and are traditionally named after their apparent shape or associated with mythological figures. The video mentions constellations as a way humans have historically mapped and named stars in the night sky.

💡Protostar

A protostar is an early stage in the formation of a star, where the cloud of gas and dust has begun to collapse under gravity but has not yet reached the temperatures and pressures to ignite nuclear fusion. The video describes the process of star formation, including the transition from a molecular cloud to a protostar.

💡Main Sequence

The main sequence is the phase in a star's life when it is fusing hydrogen into helium in its core. This is the longest phase in a star's life, during which it spends about 90% of its time. The video explains that stars like our Sun are currently in the main sequence phase.

💡Red Giant

A red giant is a massive star in a late phase of its evolution, where it has exhausted the hydrogen fuel at its core and begun fusing helium into heavier elements. The video describes the Sun's future as a red giant, expanding significantly and potentially engulfing nearby planets.

💡Supernova

A supernova is a powerful and luminous explosion that occurs at the end of a massive star's life, marking its death. The video discusses how supernovae can outshine entire galaxies and result in the formation of nebulae, which can eventually form new stars.

💡Black Hole

A black hole is a region of spacetime exhibiting gravitational acceleration so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it. The video explains that after a supernova, if the core is massive enough, it can collapse into a black hole, which has an immense gravitational pull.

💡Stardust

Stardust refers to the fine particles of dust and gas, often composed of elements created in stars, that can be found in space. The video uses the term 'stardust' poetically to describe the origins of the Earth and all life on it, emphasizing the cosmic origins of all matter.

Highlights

Stars have shaped human culture, religion, and scientific progress since the beginning of human history.

The universe contains an unimaginable number of stars, estimated in the sextillions, providing essential warmth and energy to planets like Earth.

Stars are powered by nuclear fusion, converting hydrogen into helium, generating massive amounts of energy in the process.

The sun, a yellow dwarf star, accounts for 99% of the mass in our solar system and is used as a reference point for measuring other stars.

Stars form in molecular clouds, made primarily of hydrogen and helium, through gravitational collapse that leads to the formation of protostars.

The life cycle of a star can be broken into four stages: star formation, the main sequence, the red giant phase, and eventual collapse or explosion.

Some stars fail to ignite nuclear fusion and instead become brown dwarfs, which sit between a large gas giant and a light mass star.

Main sequence stars, including the sun, spend 90% of their lifespan converting hydrogen to helium in a stable fusion process.

As stars age and use up their hydrogen, they can expand into red giants, which dramatically increase in size and cool down, signaling the end of their life cycle.

Supermassive stars can evolve into blue supergiants, hypergiants, or even Wolf-Rayet stars, which emit heavier elements during their dying stages.

Some stars, like Betelgeuse, are expected to go supernova, becoming incredibly bright and visible from Earth, possibly outshining the moon.

The collapse of a massive star can lead to the formation of neutron stars or even black holes, which have extremely high density and intense gravitational fields.

Supernovae explosions can outshine entire galaxies and leave behind nebulae, such as the famous Crab Nebula.

The largest known star, UY Scuti, is over 1,700 times the size of the sun, and if placed in the solar system, would engulf all planets up to Saturn.

The upper mass limit for stars is theorized to be around 150 solar masses, although some stars exceed this, challenging existing theories about star formation.

The future of star research is still uncertain as ongoing discoveries continue to challenge previous assumptions, revealing the endless possibilities of stellar evolution.

Transcripts

stars are awesome since mankind first

became able to comprehend our existence

we've looked up at the night sky and

seen these distant glimmers of light

and they've shaped our culture religion

and scientific progress

while you can only see a handful of

stars with the naked eye the universe

has more stars than one could possibly

imagine

shining and radiating light and heat

throughout entire galaxies and they

provide the essential warmth that

cradles life

all life on earth owes to the sun even

the animals at the sunless depths of our

ocean would not exist where not for the

sun's gravity

and the dust that once surrounded it

forming the ground we now stand on

but putting its existential

considerations aside how do stars

actually work

why is it the universe is so full to the

brim of hundreds of sextillions of stars

what makes them so common and why are

they so massive and powerful

well to understand the answer to these

questions is to understand

creation and the story of a star from

birth to death

is unparalleled in astronomy today we'll

be journeying back billions of years

as we uncover the mysteries wonders and

timelines of our own sun

and the other stars that characterize

our galaxy and the universe

firstly before we begin to look at how

they form what exactly is a star

well in short stars are massive spheres

of matter in plasma state

essentially a giant continuous explosion

of molten soup

held together by its own gravity stars

are powered for the vast majority of

their lives by nuclear fusion

an energy generating process we are

trying to recreate here on earth to

solve our energy demands

for about 90 of a star's life it turns

hydrogen into helium at its core

and the energy this releases moves to

the surface and emits stellar radiation

when it comes to our own sun we call

this emission solar winds

light heat and matter radiating across

space over billions of kilometers

for billions of years at a time stars

are the most massive component of any

given stellar system

like our own solar system the sun

accounts for even 99

of the mass of everything in our solar

neighborhood and as such we often use

measurements of the sun's mass to

estimate and categorize the weights

of various other astronomical features

the mass of our sun

is approximately 1.989 times 10 to the

27 tons

which is a number i'm not even going to

try and pronounce however

this figure characterizes one solar mass

a unit of measurement we use to assess

the mass

of other stars to that of our own and

we'll be using this measurement a lot

today

there are estimated to be as many as 300

sextillion stars in the visible universe

that's three with 23 zeroes

approximately two to four hundred

billion of these stars lie within our

own galaxy

the milky way and each mature galaxy

usually has anywhere between 100 billion

to 100 trillion stars

around 2000 of the stars in our own

galaxy are visible from earth in the

night sky

with these particularly bright local and

luminous stars being grouped into shapes

that resemble humans

objects and animals known as

constellations

which are really useful when it comes to

mapping the positions of these nearby

stars

stars can form in groups of dozens

hundreds or thousands

and these can form star clusters thanks

to the gravity of these clusters and

with a bit of help from dark matter

these clusters then combine to form

dwarf galaxies

and the dwarf galaxies then combine to

form spiral galaxies

such as the milky way spiral galaxies

retain the hydrogen and helium gas

clouds that form the earliest stars

and as such these spiral galaxies are

essentially gigantic star producing

factories

these galaxies then collide to form

giant elliptical galaxies

where some of the highest concentrations

of stars in the known universe are found

but thinking smaller than star

production on a galactic scale

how does an individual star actually

form well its life cycle is fascinating

and can be broken down into four main

stages

star formation begins with molecular

clouds

these are clouds of dust and atoms that

have been around since the earliest days

of the universe

and they have higher densities than

their surrounding space and so are held

together by their own gravity

these clouds consist of mostly hydrogen

the most abundant element in the

universe

and usually about a quarter helium with

a small fraction consisting of a few

other heavier elements

these clouds come in many different

shapes and sizes one such form is

nebulae

the orion nebula is a giant star-forming

region in the constellation of orion's

sword which is visible from earth

other areas of star formation include

the interstellar medium

clouds of hot gases and atoms that

occupy the space between stars and

galaxies

and in certain regions of colliding

galaxies where multiple hot gas clouds

collide

invariably making them much more

productive often forming what is known

as a starburst galaxy

no matter what form these clouds take

eventually they collapse into a dense

core

due to their own gravity and this

gravitational energy then turns to heat

when this collapsing cloud reaches a

relatively stable point

the embryo of a star forms known as a

protostar

these infant stars are then cooked in

this giant gaseous oven forming around

it

trapping more hydrogen and helium within

the core this process of incubation

in this manner takes about 10 million

years and when the protostar is

sufficiently developed

it begins to emit plumes of gas which

alongside external radiation helps to

drive away the gas clouds around the

outside

essentially the shell of the star these

shell gases that are driven away are

mostly dust

and are ejected outwards but still orbit

this new star

this dust begins to clump together

forming rocks and these rocks smash

together to form planetary embryos

which have the potential to become

planets earth was formed in this way

after the sun formed and complex carbon

chemistry did the rest

so essentially we all came from stardust

once

this is the beautiful process that

fragments massive gas clouds

turning them into dozens hundreds and

thousands of new stars

with child planets to watch over and

keep warm these stars are then ready to

enter the next phase

of their lives however not all stars get

this far

those stars with a particularly low mass

more comparable to the mass of jupiter

than the mass of the sun

are unable to sustain nuclear fusion of

hydrogen in their cause

an essential process for a star in the

main stage of his life

these light stars can however fuse

lithium and instead of becoming a star

they become what are known as brown

dwarfs contrary to the name

they often appear magenta in color and

often sit somewhere between

extremely large gas giant planet and

extremely light mass star

they also typically have no difference

in structure between their cores and

their utter layers

and so these failed stars never get to

become the giant radiating beacons we

see in the night sky

but for those that are massive enough to

sustain their fusion reactions

these stars burn away their incubating

molecular ovens

and enter the second and main stage of

their lives the thermonuclear fusion

stage

otherwise known as the main sequence

the main sequence accounts for about 90

of a star's lifespan

and is the point when fusion begins to

take place with the vast quantities of

hydrogen that has been trapped in the

core being fused into helium

releasing massive amounts of energy this

is what gives stars their immense heat

blinding light and incredible radiation

that travels billions of kilometers

across the near vacuum of space

a star that has just entered the main

sequence is usually in the form of a

dwarf star

the sun is a main sequence yellow dwarf

star currently

these stars are small compared to some

of the other older stars

and contain much more hydrogen than they

do helium however

fusion converts hydrogen into helium and

so the share of helium within the star

begins to rise

this increases not only the brightness

and temperature of the star itself

but the rising helium also increases the

rate of fusion in a somewhat compound

process

this process coupled with the emission

of solar winds and radiation

causes some mass to be lost however this

usually

equates to only about a fraction of a

percentage of the total mass

over a star's entire life so it's

nothing to worry about

however much more massive stars can lose

a more significant percentage of their

mass during the main sequence and beyond

because they are much less efficient how

long the main sequence lasts for depends

on the size and mass of the star and the

amount of hydrogen that star was formed

with

our sun is expected to live for around

10 billion years

whereas some supergiant stars with more

mass will be considerably less stable

and last nowhere near as long the

smallest possible main sequence stars

are known as red dwarfs

and these can fuse all of their mass

fairly efficiently and so stand to live

the longest

we don't know how long for sure but we

theorized that it could be up to one

trillion years

when these smaller and less volatile

stars have burned up their hydrogen

they will collapse into white dwarfs and

the temperature will fall

circumventing any other postman sequence

process

as for the more massive stars these are

less efficient and less stable

they fuse their hydrogen at a certain

pace and can last for billions of years

but after the hydrogen fuel at the core

has been used up

helium will start fusing into carbon and

this is where things start to get

interesting

[Music]

if a star is approximately 40 percent of

the mass of the sun or above

then when the hydrogen fuel within the

core is exhausted the star will begin to

fuse hydrogen outside of the core which

is now all helium

heavier elements are being fused in the

core as a result and these newly fusing

outer layers expand and cool down

dramatically increasing the star's size

and giving it a red color

it has entered the red giant phase this

is the stage we all love

because it is the stage that forms the

titans of the galaxy

the size of the star in its red giant

phase depends on its mass

but regardless it is ironic to think

that when a star grows to become a giant

it is actually in the stage of its life

where it's starting to die

our sun is no exception either in an

estimated five and a half billion years

the sun will exhaust its hydrogen and

balloon in size

expanding to about 250 times its current

diameter

while ejecting over a third of its mass

this will mean that mercury and venus

will both be engulfed and destroyed by

the giant

and while earth may just escape this

fiery ending the planet's surface will

be fried

as surface conditions will become

similar to that of venus

and will never be able to support life

again

red giants aren't the only things that

can be formed in this post-production

phase either stars with a mass several

times larger than the sun will expand

so much that they are classified as

supergiant stars

and stars with a mass in excess of nine

solar masses

can expand to form blue supergiants

before evolving into red supergiants

if the star is abnormally massive for

example much more than nine solar masses

we tend to classify these as hypergiants

particularly massive stars can also

evolve to become what is known as a wolf

rayet star

which emits elements heavier than

hydrogen and helium from the core

due to the intense mass loss after the

main sequence

the biggest known star in the galaxy is

commonly attributed to the beast that is

uy scooty

a more recently classified giant of the

milky way

before that it was a v-y canis majuris

which may still actually be the largest

star we've ever discovered

because all of the stars estimated to be

larger have much less accurate estimates

of their radius

but taking uy scooty as an example it is

estimated to have a radius of about 1

700 solar radii that's 1 700 times the

size of the sun

which sits at about 1.3 million

kilometers in diameter

this mind-boggling size means that where

you to place ui scooty at the center of

our solar system

it would engulf every planet asteroid

and moon as far out as saturn

to put that size in another kind of

perspective if you were to fly an

airplane around its surface

at just under 1 000 kilometers an hour

it would still take well over 1

100 years to circle it just once some of

the biggest stars we've ever discovered

have crazy numbers associated with their

size

and given that this is just within the

immediate vicinity of the milky way

you have to wonder what else could be

lurking out there

as mentioned even though these stars are

awesome they are in the dying phase of

their lives

as the outer shell layers fuse hydrogen

in these massive stars

the core becomes heavier and its

temperature rises when the temperature

is at high enough level

helium fusion begins violently which is

known as a helium flash

this causes the star to shrink in size

very quickly

and even with some variations of the

process all red giant cores

eventually become degenerate as the star

begins to die

entering the final fantastic phase of

its life

after a star's core becomes degenerate

it starts to shrink

the radiation from the surface increases

dramatically

creating pressure on the outer shell

which in turn strips back the outer

shell

layers depending on the mass of the star

in question

a number of very different outcomes can

then occur

if what is left of the stripped back

star is now less than 1.5 solar masses

then the star will shrink to a size

comparable to the earth

and will become a white dwarf white

dwarfs are not heavy enough for gravity

to continue compressing them

and the electron matter inside the star

is no longer in plasma state

eventually white dwarfs burn themselves

out emitting no more light or heat

and enter a theoretical stage known as a

black dwarf

or a cold star the lightest stars end

their lives fairly tamely

after they have finished their main

sequence they become far smaller and

from there they just

fade away when it comes to more massive

stars

these can start to produce iron in their

cores by fusing helium into heavier

elements

if the iron core is above 1.5 solar

masses then the shrinking and receding

star will no longer be able to support

its own mass

it will begin fusing heavier elements

iron nickel and cobalt

and this will mark the final moment

before a fantastic death

no heavier elements can be fused and so

no new radiation is produced to

counterbalance the gravity of the core

keeping the star intact the star can no

longer keep itself hot enough

and electrons will be driven into

protons forming neutrons neutrinos and

gamma rays

causing the star to violently implode

this collapse causes a shock

wave which causes the outer layers of

the star to blow up in a brilliant

explosion

known as a supernova supernovae

are among some of the brightest things

in the universe sometimes they are so

bright that they even outshine their

entire

galaxy the explosion disperses the

star's outer layers

leaving a remnant in the surrounding

area these remnants are called nebulae

one such stellar ghost is the crab

nebula

in fact this is exactly what is

predicted to happen to a nearby

supergiant star in the milky way very

soon

beetlejuice is an extremely luminous red

supergiant star

over 900 times larger than the sun

located 640 light years away from earth

it is one of the 10 brightest visible

stars in the night sky

and is highly unstable and beginning to

shed its outer layers

when it finally enters the iron fusing

process and implodes

it will go supernova and its brightness

will rise to billions of times brighter

than our sun

documented cases of supernova explosions

have only happened a few times

throughout history

and none have been as close to us as

beetlejuice is

so when it finally does blow its banks

the resulting brightness will be visible

from earth during the daytime

and the night time with some predicting

that it will even outshine the moon for

the best part of the year

given that the light delay is over 600

years it could have already happened and

the light is traveling towards us now

so there's a slim chance that uri

watching this video may be able to

witness

beetlejuice go supernova and outshine

the rest of the galaxy

in our lifetimes as for when it will

happen well we simply cannot tell

after the brilliant visual display of

the supernova has occurred

the cause of these stars can still

continue to evolve

in some cases the core will collapse in

on itself and form a very dense

comparatively minuscule object with an

immense gravitational field relative to

its size

known as a neutron star what was once a

massive star capable of engulfing

millions of kilometers

collapses in on itself to form an object

no more than 30 kilometers wide

in some cases these celestial bodies

will rotate rapidly

and sometimes emit beams of radiation

detectable from the earth

called pulsars it was through this

phenomenon

that in 1967 a signal named lg m1 was

discovered

a radio signal from a pulsar that was

initially attributed

to a transmission from an alien

civilization

most neutron stars have such strong

gravity fields that were you to drop a

teaspoon from shoulder height to the

ground while standing on one

the spoon would reach speeds in excess

of 22 000 kilometers per hour

before it collided with the ground

however that still isn't the most

extreme thing massive dying stars can

form

not all post supernova stars collapse to

form a dense neutron star

some take it a step further if the strip

back core in question is in excess of

four times the mass of the sun

then the resulting force of the

implosion will be so great

that it will compress the entire core

into a single microscopic point with

near infinite density

known as a singularity the resulting

gravity field is so strong

that past a certain point not even light

can escape

the massive collapsing star has now

formed a black hole

black holes are some of the strangest

things in the universe and are the

ultimate all-consuming eventuality for

the most massive stars

while these black holes aren't usually

the supermassive black holes at the

centers of galaxies

they can still achieve some pretty

impressive sizes

whatever happens to a star when it dies

it's never usually boring

so there you have it we've now covered

the lifecycle of a star

from its formation to its death these

massive thermonuclear explosions are

responsible for shaping so much of the

universe you see around you

where galaxies are the legions of the

cosmos stars of the centurions

but the question is is there a size

limit that stars cannot exceed

well theoretically yes there should be a

size limit for stars

and this is not due to the mechanics of

the star itself but is more to do with

the star-forming molecular clouds

these clouds cannot exceed a certain

mass when incubating stars or they would

lose their star-forming properties

so with this in mind some papers have

speculated

that the upper bound for stars should be

about 150 solar masses

but then again we've discovered stars

such as the blue hypergiant pistol star

which are estimated to be closer to 200

solar masses

so no one really knows for sure

ultimately we can conclude

on an upper bound limit for mass but

when it comes to size

there are a few more variable factors

the largest known star is about 1

700 times the diameter of the sun and

some predict that cool supergiant stars

could grow to as big as 2

600 times the sun's size but others

dispute this

principally there is no absolute cut-off

point that we can send the benchmark out

because we simply don't know enough

about the detailed long-term process of

star formation and evolution

and who's to say that in the future an

abnormal style won't be formed which is

greater than any other style that has

ever existed

the idea of an upper size limit hinges

on the assumption

that the number isn't fluid but we

simply don't know

and even a survey sample of an entire

galaxy doesn't really provide the clear

picture we need to gauge a better

understanding of star metrics

however every discovery we make

challenges old ideas

and so the only way we can ever conclude

on star size limits

is to continue to discover observe and

research these giants of creation

stars are truly some of the most

wonderful things in the universe

with our wealth of knowledge now it's

easy to lose sight of them

as we think bigger galaxies galaxy

clusters and the rest of the universe

but when you break a galaxy down to its

key component you see the root cause of

so many defining features of our

universe

all because gravity attracts hydrogen

and helium atoms together

and given enough time complex processes

produce these brilliant stellar firework

displays

from the dwarfs right up to the

hypergiants each star has its own story

to tell

its own solar system and its own

possibilities for supporting life

and with 306 tillion stars out there

and hundreds of six billions more beyond

the boundary of the observable universe

the possibilities really are endless

[Music]

you