Life cycle of 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