1. Stars: Old Age, Death, and New Life
BC Science Probe 9
Section 13.4
Pages

2. Stars Stars age as they use up their hydrogen.
After millions or billions of years, a star will enter the last stages of its life.
At the end, a star can either fade out of existence, or explode in a life-renewing cycle!

3. Hertzsprung-Russell
A star’s mass determines its brightness, colour, size, and how long it will live.
This information is organized in a diagram called the Hertzsprung-Russell (H-R) diagram which plots the lives of stars.

5. Hertzsprung-Russell
An H-R diagram shows the temperature and luminosity of stars.
Luminosity is energy output and the Sun is assigned the value of 1.

6. Hertzsprung-Russell
Most stars fit into the main sequence of the H-R diagram.
This is the diagonal band on the diagram.
Where it fits on the main sequence depends on its mass.

7. Hertzsprung-Russell
Our Sun has 1 solar mass, and it is the star to which all others are compared.

8. Hertzsprung-Russell
In the lower right of the diagram are the cooler, reddish stars that are small and dim.

9. Hertzsprung-Russell
In the upper left are the massive, very bright, hot, bluish stars.
The blue giants.

10. Hertzsprung-Russell
The cooler red giants ( solar masses) and the super giants (10-70 solar masses) are found off the main sequence to the upper right.

11. Hertzsprung-Russell
The white dwarfs which are very hot and about 1/3 of a solar mass are in the lower left.

12. Hertzsprung-Russell
The stars in the H-R diagram represent different stages in the lives of stars as their fuel is consumed.

13. Red Giant to White Dwarf
After 10 billion years as a main sequence star, most of the Sun’s hydrogen will be converted to helium.
The helium forms a core inside a shell of the remaining hydrogen.

14. Red Giant to White Dwarf
Less hydrogen = less energy = less outward flow of energy.
This causes the core to shrink and the shrinking/contraction reheats the rest of the hydrogen and starts fusion again!

15. Red Giant to White Dwarf
Even though the core is shrinking, the outer layers will expand and then cool.
This expanded, cooler Sun will eventually be a red giant.

17. Red Giant to White Dwarf
The Sun will expand for millions of years.
It will engulf Mercury, Venus, and maybe even the Earth!

19. Red Giant to White Dwarf
Once the hydrogen is actually all used up, the core will heat to a temperature high enough to begin helium fusion.

20. Red Giant to White Dwarf
Helium fusion will continue the expansion.
It will also produce heavier elements like Carbon and Oxygen.

21. Red Giant to White Dwarf
Now it is a fully formed red giant.
It will have several thousand times its original brightness!

22. Red Giant to White Dwarf
Red giants give off dust and gas, so they begin to lose mass.
Even a star that starts at a mass of up to10 solar masses will eventually lose enough mass to become a stable white dwarf.

23. Red Giant to White Dwarf
A white dwarf will have a mass no larger than 1.4 solar masses and it is compressed to the size of the Earth.

24. Red Giant to White Dwarf
A star that has a mass over 10 solar masses will explode as a supernova.

25. Red Giant to White Dwarf
The Sun is 1 solar mass, so it will become a white dwarf.
It will release particles that will collide with the matter it shed during its last stages as a red giant.

26. Red Giant to White Dwarf
The energy from these collisions of particles will illuminate the clouds of gas and dust and create a nebula…
What can a nebula form?

28. Red Giant to White Dwarf
The white dwarf, or the remains of the Sun, will keep its place in the Milky Way until it burns out and becomes a black dwarf.
It will no longer be visible.

29. Supernovas
The explosion of a star in which the star may reach a maximum intrinsic luminosity one billion times that of the Sun.

31. Supernovas They may only last a few months.
The energy that they generate can drive the fusion and formation of all of the elements on the Periodic Table.

32. Neutron Stars
If a star starts out at solar masses, the supernova will produce a neutron star.

33. Neutron Stars The core of a neutron star is made mostly of neutrons.
They are so tightly packed together that 250 ml (1 cup) of the core would have a mass of millions of kilograms!

34. Neutron Stars
A pulsar is a kind of neutron star that sends out light and a beam of very high-energy radio waves.
It rotates giving off the beam of energy kind of like a light house.

35. Black Holes
If a star has an initial mass of over 50 solar masses, it will become a supernova and produce very heavy elements like iron and nickel.

36. Black Holes
If the mass left behind is more than 4 solar masses, the core will collapse in on itself.

37. Black Holes
The object’s mass is still immense, so its gravitational pull is also immense.
Not even light can escape.
It has become a black hole.

39. Black Holes
A black hole of 10 solar masses would only be 60 km in diameter!

40. Black Holes
Black holes are very difficult to find because they are small and do not give off light.
Many stars exist as binaries ( 2 stars circling each other), this was how the first black hole was discovered.
A blue giant and its invisible companion.

42. Black Holes
The first black hole was found in the constellation Cygnus.
The black hole pulls gas from the blue giant.
The gas heats up and emits X-rays which allowed the black hole to be detected.
The blue giant has a solar mass of 27 and the black hole (Cygnus X-1) has a solar mass of 14.