9.2 Classification of stars

• Main sequence stars lie on the H-R diagram with high temperature and moderate luminosity.
• Match the star type with its description:

  Main Sequence ↔️ High temperature, moderate luminosity

  Giant Stars ↔️ High luminosity, low temperature

  Dwarf Stars ↔️ Low luminosity, high temperature
• Where do most stars lie on the H-R diagram?

  Main Sequence
• Red giants have high luminosity but low surface temperature.
• What does the Hertzsprung-Russell (H-R) diagram show the relationship between?

  Luminosity and temperature
• Giant stars have high luminosity but low surface temperature.


  True
• The main sequence is a diagonal band on the H-R diagram.


  True
• Red giants are more luminous than main sequence stars but have lower surface temperatures.


  True
• Where are white dwarfs located on the H-R diagram?

  Bottom left
• What is the final stage of stellar evolution for neutron stars?

  Pulsars
• Stages in the formation of a neutron star

  1️⃣ Massive star exhausts its fuel

  2️⃣ Core collapses

  3️⃣ Supernova explosion

  4️⃣ Formation of a neutron star
• What is the approximate diameter of a neutron star?

  20 km
• The H-R diagram plots a star's luminosity against its surface temperature.


  True
• The main sequence on the H-R diagram represents the longest and most stable phase of a star's life.


  True
• What two properties characterize white dwarfs?

  Extremely high density and small size
• What event leads to the formation of neutron stars?

  Supernova explosion
• The spectral classification of stars is based on their surface temperature and absorption lines in their spectra.
• What is the hottest spectral class of stars?

  O
• What type of star forms from the collapsed core of a supernova explosion?

  Neutron Star
• Main sequence stars fuse hydrogen into helium in their cores.
• The surface temperature of main sequence stars ranges from 3,000 K to 50,000 K.

  True
• What is the typical surface temperature range for supergiants?

  3,500-8,000 K
• The density of a neutron star is approximately $10^{14}$ g/cm³.
• Match the star type with its property:

  White Dwarfs ↔️ Low luminosity, high density

  Neutron Stars ↔️ Collapsed cores of supernovae
• White dwarfs cool over billions of years
• White dwarfs have low luminosity but high surface temperature.


  True
• Match the feature of the H-R diagram with its description:

  Main Sequence ↔️ High temperature, moderate luminosity

  Giant Stars ↔️ High luminosity, low surface temperature

  Dwarf Stars ↔️ Low luminosity, high surface temperature
• Main sequence stars fuse hydrogen into helium
• Red giants and supergiants have lower surface temperatures than main sequence stars
• Neutron stars have higher density than white dwarfs.


  True
• Order the steps in the formation of a neutron star:

  1️⃣ Massive star exhausts its fuel

  2️⃣ Core collapses

  3️⃣ Supernova explosion occurs

  4️⃣ Collapsed core forms a neutron star
• Match the spectral class with its surface temperature:

  O ↔️ > 30,000 K

  G ↔️ 5,200 - 6,000 K

  M ↔️ 2,400 - 3,700 K

  A ↔️ 7,500 - 10,000 K
• Order the life cycle stages of a star from earliest to latest:

  1️⃣ Main Sequence

  2️⃣ Red Giant

  3️⃣ Supergiant

  4️⃣ White Dwarf
• Match the stellar remnant with its characteristic:

  White Dwarf ↔️ Earth-sized, carbon and oxygen

  Neutron Star ↔️ 20 km diameter, neutrons
• White dwarfs cool over billions of years and neutron stars can become pulsars.


  True
• Neutron stars emit powerful radio waves as they cool.

  True
• Neutron stars are the collapsed cores of massive stars after a supernova explosion
• What type of stars lie on the main sequence of the H-R diagram?

  Most stars
• What is the typical surface temperature range of red giants?

  3,000-5,000 K
• White dwarfs have low luminosity but high surface temperature