1. The Life Cycle of a star
By Ramunė Stabingytė and Kotryna Bieliauskaitė
Kaunas “Vyturys” cathalic secondary school

4. What is a Star? A star is a huge sphere of very hot glowing gas.
When stars are grouped together we call them constellations.
The big dipper is constellation that we see often.

5. The Sun The Sun is the only star in our solar system
All eight planets, comets, and an asteroid belt, revolve around the Sun.
The Sun is a yellow, medium sized star.

6. Classifying Stars
Stars are classified according to their temperature and brightness.
Hot Stars are Blue or White
Cooler Stars are Red or Orange

7. Classifying Stars Cont…
A young star is called a dwarf star
They can be colored red, yellow, or white.
Our Sun is a yellow dwarf
Older Stars are called Supergiants
They can be colored red or blue.

8. The Timeline of a Star
Our Sun is an average star. The chart below shows the lifecycle of our sun over billions of years.

9. Birth of a star
In space, there are huge clouds of gas and dust called nebulas.
These clouds are made up of hydrogen and helium and are the birthplace of new stars.
Gravity pulls the hydrogen gas in the nebula together and it begins to spin,
As the gas spins faster and faster, it heats up and is known as a protostar.

10. Protostar The second stage of star creation.
At this point the temperature eventually reaches 15,000,000 °C.
The cloud begins to glow brightly.
At this stage, it contracts a little and becomes stable and is called a main sequence star.

11. Main sequence star
A star will remain in this stage, shining for millions or billions of years to come.
As the main sequence star glows, hydrogen in the core is converted into helium by nuclear reactions.
Our sun is a main sequence
star.

12. Red giant phase
When the hydrogen supply in the core begin to run out, the core becomes unstable and contracts.
The outer shell of the star starts to expand.
As it expands, it cools and glows red.
The star has now reached the red giant phase.

13. White dwarfs
Gravity causes the last of the star’s matter to collapse inward and compact, this is the white dwarf stage.
At this stage the star’s matter is extremely dense.
White dwarfs shine with a white hot light.
The star has now reached the black dwarf phase in which it will forever remain.

14. Massive stars
Once massive stars reach the red giant phase, the core temperature increases.
Gravity continues to pull carbon atoms together as the temperature increases forming oxygen, nitrogen, and eventually iron.
At this point, fusion stops and the iron atoms start to absorb energy.
This energy is eventually released in a powerful explosion called a supernova.

15. Supernova A supernova can light up the sky for weeks.
The temperature in one can reach 1,000,000,000 °C.
The supernova then either becomes a neutron star or a black hole.

17. Neutron star Neutron stars spin rapidly giving of radio waves.
If the radio waves are emitted in pulses, the neutron star is called a pulsar.

18. Black hole
The core of a massive star that has 8 or more times the mass of our Sun remains massive after the supernova.
It has now become a black hole which readily attracts any matter and energy that comes near it.
Black holes are not visible, they are detected by the X-rays which are given off as matter falls into the hole.

20. How do the sizes of the stars compare?

21. Thank you for attention 