How do Stars Work?
Summary
TLDRThis 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
🌟 The Importance and Vastness of Stars
💫 The Formation of Stars: From Gas Clouds to Fusion
☀️ The Main Sequence and Life Stages of Stars
🔥 The Future of Our Sun and the Fate of Massive Stars
🌌 Supernovae, Neutron Stars, and Black Holes
Mindmap
Keywords
💡Star
💡Nuclear Fusion
💡Solar System
💡Galaxy
💡Constellation
💡Protostar
💡Main Sequence
💡Red Giant
💡Supernova
💡Black Hole
💡Stardust
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
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