Chapter 19 Past Lifetime Of Stars To End

Question 1

What is the hertzprung Russel diagram about

What is on y and x axis
- what to take care about x axis
- what if it’s log?

Answer 1

It’s a diagram to represent the Lifecycle of stars , as they change in luminosity and Temperature

Y axis is luminosity, and x axis is temperature, but the TEMPERTAURE is in REVERSE order

2) also take care if it’s logarithmic form, the change in 5 to 4.9 is many orders for example

Question 2

How to think about TEMPERTAURE change on the hertprung Russel (what causes temp to increase and decrease)?

Answer 2

VOLUME
- as a star expands due to radiation pressure, the energy gonna be dispersed over larger volume so temo DECREASES
- thus when it goes red giant and fully expands, the TEMPERTAURE will decreases as its same energy output ish over a LARGER VOLUME

• or when volume decreases ( so in collapse), the temp INCREASES! So white dwarf example will have very high temp,

Question 3

What is luminosity on the y axis compared to

So if it’s in Log form , how to get the actual luminosity?

Answer 3

This is standard to the SUNs luminosity

2) will have to e value, then multiply this by the LUMINOSITY OF THE SUN

Question 4

What even is luminosity

How can we think about it

Answer 4

This is the total power radiated out if thr star and related to its BRIGHTNESS

Can think about in terms of energy output, so to do with fusion etc

Question 5

Explain all the positions of the sections of the hertepsunr diagram,

Answer 5

From bottom right to top left, it is kinda straight line . These are all MAIN SEQUENCE STARS

Then bottom left is WHITE DWARF

Then half way through main sequence towards top right are RED GIANTS

and line on top is SUPER RED GIANTS

Question 6

explain why TEMPERATURE increases with mass too?

1) main sequence stars

-explain luminosity and why it goes up top left
So which stars are heaviest

Answer 6

The line in the middle represents these, all stars here are stable as they fuse hydrogen to counter the grav pull

• here the MASS IS PROPRTIONAL TO LUMINOSITY, because the more mass (going towards top left), the more grav pull, and thus more fusion needs to be done to counter grav pull and thus has MORE LUMINOSITY

2) therefore biggest stars heaviest are top left with most mass, and likely these ones will become super red giants after supernova

3) temp increases bevause heavier stars are more hot as more gpe can be converted to Ke = have hotter cores

Question 7

Why does when a main sequence star become a red giant it move towards too right?

• more luminous?
• colder?

Answer 7

1) increase in luminosity due to it using hydrogen in shells for hydrogen , rate of fusion increases , so more energy output
2) however this causes the star to expand , and so more energy over larger volume decrease temp , thus it moves up and to the right

Question 8

Why does after a red giant collapse and release planetary nebulae and become a white dwarf is it bottom left ?
- luminosity decrease?
- temp increase

Answer 8

1) luminosity devreased to very very small values. This because no more FUSION Takes place = no more energy release
2) VERY hot as it’s very dense and small, after the collapse to leave the core

Thus bottom right

Question 9

Why do super red giants move from top left to top right as they live ?

• why does luminosity stay pretty high
• why does temp decrease to very low

Answer 9

1) LUMINOSITY stays the same . As the life continues, fusion of heavier elements keep happening before supernova, and thus the energy output is mainiter

2) temp DECREASES!
- the fusion of heavier elements actually results in the red supergiant to EXPAND AND ESPAND.
- more energy over huger volume = less TEMP