Brief Information about Stars

1. TUMKUR UNIVERSITY
DEPARTMENT OF STUDIES AND RESEARCH IN PHYSICS
SEMINAR
SUBJECT:- ASTROPHYSICS
TOPIC:- THE LIFECYCLE OF A STARS
SUBMITTED BY:
ASHA.C
3RD SEM SUBMITTED TO:
REG NO: 20PPH202 SANDEEP .D.H
DOSR IN PHYSICS FACULTY OF PHYSICS
DOSR IN PHYSICS

2. THE LIFECYCLE OF A
STARS

3. WHAT IS STAR ?
A Star is any massive self luminous celestial body of gas, mostly hydrogen
and helium that shines by radiation derived from its internal energy
sources.
Stars are found in huge groups called Galaxies . A galaxy is collection of
stars and planets that are held together by gravity.
The galaxy contains hundreds of billions stars . there are many billions of
galaxies in the universe.
Only a very small percentage are visible to the naked eye.
The nearest star to Earth is the sun.

5. Birth of stars
Interstellar space is filled with particles of dust and gases , mostly hydrogen
and helium . these particles comes together to form a gas cloud called nebula.
When this gas cloud attains mass more than one thousand solar mass , it
begins to contract under the effect of its own gravitational force.
 As cloud contracts, its temperature rises to very high value and it begins to
radiate energy due to nuclear fusion which helps the cloud contracts
further.
Nuclear fusion is a reaction in which two or more atomic nuclei of low
atomic number are combined to form heavier nucleus with the release of

9. What happens during the stages
Stage 1 :- Nebula
 A cloud of dust and gas.
 When the gas and dust contracts under gravity ,
a protostar is born.
 Some nebulas are several light years in diameter and could be 100 times
bigger than our solar system.

10. Protostar
The cloud of gas and dust begins to clump together due to gravity , and
gives off light due to internal heating. This clump is called Protostar.
The interior of the cloud has heated to over 10,000kand a protostar
forms at the center .
Earliest stage of a stars life.

11. Stage 2:- Main sequence
 Second stage of life Nuclear fusion starts as gas cloud becomes
denser and hotter.
 The internal heat pressure outward balances the inward
gravitational pressure.
 Star stops collapsing and is stable . creates the Intense energy found
in stars.
 This is the longest stage of life of star.
 How long the stars stays on the main sequence fusing hydrogen
depends on its mass.

12.  Larger stars (up to 20 times the size of our sun) are hotter and burn
up their fuel faster ,have shorter lives(million of years).
 Low mass stars lives longer than high mass star.
 This is the stage our Sun is currently in.
 Main Sequence stars are the central band of stars on the
Hertzsprung-Russell Diagram.
 90% of all stars are Main Sequence stars.
 It takes about 10 billion years to consume all the hydrogen in a Main
Sequence star.

14. Stage 3 :- Red giant and Red super giant
 When the hydrogen in a main sequence star is consumed the forces
suddenly become unbalanced . Mass and gravity cause the
remaining gas to collapse on the core.
 A red giant is formed when a star runs out of hydrogen at its core
and stars fusing hydrogen into helium just outside the core releasing
energy and expanding the star.
 Fusion of helium into carbon begins. Forces regain balance.
 Outer shell expands from 1 to at least 40 million miles across.
 Red Giants last for about 100 million years.

16. Red super giant
 If the mass of a star is 3 times that of our sun or greater, then the
Red Giant will become a Red Supergiant.
 When a massive Red Giant fuses all of the helium into carbon ,
fusion stops and the outer layers collapse on the core.
 This time, there is enough mass to get the core hot enough to start
the fusion of carbon into iron.
 Once fusion begins , the star will expand to be between 10 and
1000 times larger than our sun.

18. Stage 4 :- Planetary Nebula
 The Planetary Nebula phase is a final stage in a low mass star’s life.
 When the star runs out of helium , it gives out a large burst of
energy and pushes its atmosphere into space, creating a planetary
nebula.

20. Stage 5:-Supernova
 A Supernova is a explosion of a massive Supergiant star. It may shine
with the brightness of 10 billion suns.
 The total energy output may be 10^44 joules , as much as the total
output of the sun during its 10 billion year lifetime.
 All matter heavier than carbon was produced in the cores of the
stars that exploded as supernova.
 Distribution of heavy elements into space.
 Recent supernova : 1987 Large Magellanic cloud

22. Stage 6 :- White dwarf
 This is next Phase of the Red giant.
 A white dwarf is very dense , its mass is comparable to that of the
sun, while its volume is comparable to that of earth.
 White dwarfs form after the helium flash, where the helium ash at
the core of the star ignites . This usually leads to enough increase in
energy to further fuse atoms into carbon, nitrogen, and oxygen.
 The outer layer of the red giant explodes out into space leaving the
white core behind. Has no energy but glows faintly from left over
heat.
 When a White dwarf stops glowing it becomes a black dwarf , the
star is dead( temperature-15,000k).

24. Stage 7 :- Neutron star
 If the collapsing stellar core at the center of a supernova contains
between about 1.4 and 3 solar masses, the collapse continues until
electrons protons neutrons are expelled, producing a neutron star.
 Protons and electrons left after a supernova are forced to combine to
produce very dense neutron star.
 The temperature inside a newly formed neutron star is from around
10^11 to 10^12.

26. Stage 8:- Black hole
 Black hole is formed by the gravitational collapse of a massive
star.
 A Black hole is a region of spacetime where gravity is so strong that
nothing – no particles or even light can escape from it .The
boundary of no escape is called event horizon.
 This star ranges from the mass of about 3 to several tens of solar
masses.

28. Thank You