Stars

Question 1

Define planets

Answer 1

• has mass large enough for gravity to give it a round shape
• has no fusion reactions
• has cleared it orbit of other objects like asteroids

Question 2

What are planetary satellites?

Answer 2

• a body in orbit around a planet

Question 3

What’s an example of a planetary satellite?

Answer 3

Moon or Satellite

Question 4

Define a comet

Answer 4

Small irregular bodies made of ice, dust and rock.

They orbit the sun in elliptical orbits

Question 5

How do the majority of comets orbit?

Answer 5

Elliptical orbits

Question 6

Define a solar system

Answer 6

A system of plants that orbit a sun

Question 7

Define a galaxy

Answer 7

A collection of stars and interstellar dust.

Question 8

What does a Hertzsprung- Russell diagram show?

Answer 8

The relationship between the luminosity of a star and its temperature

Question 9

What star has a very high temperature but low luminosity?

Answer 9

White dwarf

Question 10

Name 3 characteristics of white dwarfs

Answer 10

• Very dense
• no fusion reaction occurs
• surface temperature up to 30000K

Question 11

Define the protostar stage

Answer 11

A sphere of hot gas that allows hydrogen gas to undergo fusion and produce helium nuclei

Question 12

Define electron degeneracy pressure

Answer 12

The pressure when electrons are squeezed together as the core of a star collapses. Which prevents further gravitational collapse

Question 13

Define Chandrasekhar Limit

Answer 13

The maximum mass of stars where electron degeneracy pressure applies.
(1.44M©️)

Question 14

What are the characteristics of a black hole

Answer 14

~very dense
~has mass greater than 3M
~has a gravitational field so strong light cannot escape

Question 15

How does a low mass star become a red giant?

Answer 15

A star runs low on Hydrogen and less energy is released by fusion so the core cools down and collapses.
Fusion occurs in the outer shell

Question 16

How is a planetary nebula formed?

Answer 16

When the outer shells of a red giant cools and drifts away

Question 17

What’s the mass of a massive star

Answer 17

> 10M

Question 18

State Wien’s Law

Answer 18

The maximum wavelength of a black body is inversely proportional to temperature
Lambda x Temperature = constant

Question 19

State Stefan’s Law

Answer 19

The total power radiated per unit surface area of a black body is directly proportional to the fourth power of temperature.
L=4πr²σT⁴

Question 20

What is the path difference of two adjacent waves at first order maxima?

Answer 20

λ

Question 21

Explain how absorption line spectra works

Answer 21

• Light with a continuous spectrum passes through a cooler gas.
• some photons are absorbed by the gas, making electrons excited
• specific wavelengths of photons are absorbed, creating dark lines in the continuous spectra

Question 22

Explain why a red giant is brightest when it is at its coolest

Answer 22

• Red giants have a large surface area
• and radiate large amounts of energy
• so greater intensity of light making it bright

Question 23

Explain how low mass stars like our Sun is formed

Answer 23

• Gravitational attraction forms clouds of dust which become denser.
• gravitational energy is transferred to thermal energy
• protostar- a sphere of hot gas allows hydrogen to fuse and form helium nuclei.
• a stable equiulibrium is formed where radiation pressure from fusion counteracts compression due to gravity.

Question 24

Explain how massive stars form red supergiants to supernova to black hole

Answer 24

• A hotter core means Helium nuclei fuse into heavier elements.
• Helium nuclei have enough KE to overcome repulsive forces.
• Massive nuclei fuse together so multiple shells form.
• The red supergiant has an iron core which doesnt fuse.
• The star becomes unstable and implodes forming a supernova
• Gravitational collaspe compresses the core, forming a black hole.

Question 25

How is a neutron star formed from a supernova?

Answer 25

From the supernova explosion, electrons and protons begin to form neutrons due to gravitational compression forming a dense neutron star.