welcome to new episode of Space Science Series
today's episode is stars in this episode
we are going to understand what are the
stars how they take birth and different
phases of their life at dark night if we
look at the sky we see stars scattered
everywhere across the sky what are the
stars actually they are huge spheres of
hot gases held together by their own
gravity estimated stars in the
universe till date are 3 × 10 raise to 23 only six to ten thousands of them are
visible by naked eye they are at
different distances from us as well as
they are of different sizes temperatures
colors and brightness star takes birth
inside hydrogen dust clouds called
nebulae thousands of year it takes to
contract and form a dense core because
of huge density of core it's pressure
and temperature rising so high this
phase of generation of star is called as
T-Tauri phase millions of years later
when temperature becomes about 15
million degree Celsius nuclear fusion
begins to set a longest phase of star's
life called main sequence let's see why
stars have different brightness and
colors stars are hot dense spheres of
hydrogen and helium gas the light and
heat they produce because of nuclear
chain fusion reaction
two hydrogen atoms are fusing together
to produce one helium atom and giving up
tremendous amount of energy the nuclear
fusion occurs at the core of the star
the amount of heat and light produce is
depend on how much fuel they have faster
the rate of fusion brighter the star the
denser the core
that means massive the star higher will
be the rate of fusion and brighter will
be the star stars have atmosphere too the
gases present in their atmosphere
outside the core absorbs light produced
in core and gives at specific wavelength
depending upon elements of gases the
atmosphere because of that continuous
spectrum of light has gaps in it German
physicist Max Planck proved that stars
gives off light of different colors based on
their temperature hotter star gives blue
line spectrum while cooler star gives
red color light Cecilia Payne-Gaposchkin
proved that color of the light comes out
from a star is dependent on both the
things temperature as well as element of
the stars atmosphere even if stars like
sun are giving green color spectrum more
than any other color but our eyes see mixed
colors together as white some light of
shorter wavelength like purple blue and
green get scattered away by nitrogen
molecules from Earth's atmosphere sunset
looks orange or red because very thick
layer of atmosphere is there between our
eyes and sun at the horizon
so all blue light scattered away and we
see sky and Sun red or orange
Star classification system given by
Cannon and Payne-Gaposchkin is still
used today according to the temperature
stars are classified assigning letters
from o to Y hottest stars are of type O
slightly cooler stars are of type B and
followed by a F G K and M each group
divides into ten subgroups like G group
is divided into subgroups G1 G2 up to
G10 in past few decades even cooler
stars are discovered they are assigned
letters L P and . Y type of stars has
minimum temperature our has surface
temperature 5500 degree Celsius
and it is G2 type of star the brightest
star will look in the night sky is
Sirius which is A0 type of star two
things are very necessary to know about
any star those are temperature of the
star and its distance from us by knowing
these two things we can measure its size
also how much amount of energy that star
is giving off nothing but luminosity can
be calculated easy in 1910 a Jenner
Ejnar Hertzsprung and Henry Russel created
one diagram which was major step towards
stellar evolution the diagram known as
H-R diagram which shows relationship
between stars magnitude or luminosity
versus effective surface temperature
more simply to say brightness versus
temperature every star can be plotted on
this diagram Sun is plotted on this diagram
with luminosity equals to 1 and surface
temperature equals to 5500 degree celcius
the most prominent region is diagonal
going from upper left hot and bright
stars to lower right cooler and less
bright stars and as main-sequence in
lower left stars are hot and blue but
very faint that's why they must be
dwarfs, above the main sequence there
are giant stars and at upper right
region there are stars which are cooler
but still bright that's why they must be
super Giants the smallest star found in
universe is OGLE-TR-122b which is a
red dwarf having diameter only 0.12 times the Sun diameter the biggest
star found in the universe is uy scuti
which is a red supergiant having
diameter 1708 times the Sun
diameter stability of main sequence
stars for billions of years is because
of balance of two forces acting in
opposite direction to each other one is
gravity which acts towards the core and
the force because of tremendous pressure
of gases inside or acts away from core
opposite to gravity what happens with
stars then their fuel come to an end
fusion reaction stops with the end of
hydrogen in the core but because of
higher temperature it continues to emit
energy into the space as fuel has been
ended already and energy emission is
continued temperature of star begin
decreasing as nuclear fusion has stopped
pressure of gases inside core starts
reducing gravitational force dominates
this opposing force and star begins
contracting its pressure and
temperatures start to increase if this
temperature goes beyond the temperature
requirement of helium fusion reaction
then the core starts
nuclear fusion again
helium is converted into carbon and
oxygen by giving out tremendous amount
of energy which is even more than
hydrogen fusion reaction this effect
further expansion of star star becomes
bigger as compared to its previous sites
in expanded condition star becomes
stable again it begins contracting when
helium fuel ends and new cycle begin in
which carbon fuses into neon and
magnesium again star expands its surface
temperature becomes though and as low
temperature sources in its red light it
looks as red and huge so named as red
super shine in fact each star doesn't
become red supergiant what will be its
future after hydrogen fuel ends is
depend on the mass of star if the mass
of star is less than 0.008 times the mass of Sun then it
remains brown dwarf if mass of star is
in between 0.008
and 8 times the mass of Sun then it
becomes white dwarf if mass of star is
in between 8 and 25 times
the mass of Sun then it becomes neutron
star and if mass of star is above 25
times the mass of Sun then it becomes
black hole that's all for this episode
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comment below thanks for watching
