Interstellar Medium
  • 1. What is the interstellar medium (ISM) primarily composed of?
A) Gas and dust
B) Liquid water
C) Rock formations
D) Plasma
  • 2. Which type of electromagnetic radiation is most commonly used to observe the interstellar medium?
A) X-rays
B) Visible light
C) Radio waves
D) Gamma rays
  • 3. What is the process by which interstellar dust grains align themselves with magnetic fields?
A) Radiative torque alignment
B) Ionization imbalance
C) Microwave heating
D) Heat conduction
  • 4. What term is used to describe regions in the ISM that contain a higher density of gas and dust?
A) Molecular clouds
B) Supernova remnants
C) Reflection nebulae
D) H II regions
  • 5. What is the most abundant element in the interstellar medium?
A) Hydrogen
B) Oxygen
C) Carbon
D) Helium
  • 6. What is the main component of interstellar dust grains?
A) Platinum
B) Gold
C) Silicates
D) Diamonds
  • 7. What is believed to be a major reservoir of carbon in the interstellar medium?
A) Carbon monoxide (CO)
B) Polycyclic aromatic hydrocarbons (PAHs)
C) Carbon dioxide (CO2)
D) Methane (CH4)
  • 8. What color do reflection nebulae appear to be?
A) Green
B) Red
C) Blue
D) Yellow
  • 9. What type of gas cloud emits its own light due to ionizing radiation from nearby hot stars?
A) Reflection nebula
B) H II region
C) Dark nebula
D) Supernova remnant
  • 10. What is the approximate number density of molecules per cubic meter in molecular clouds within the ISM?
A) 100 ions/m3
B) 1 billion (109) molecules/m3
C) 1 trillion (1012) molecules/m3
D) 10 quadrillion (1016) molecules/m3
  • 11. Which phase of the ISM is characterized by temperatures around 8000 K?
A) Coronal gas
B) Cold dense phase
C) Warm ionized medium
D) Photodissociation region
  • 12. What percentage of the ISM's mass is composed of dust?
A) 1%
B) 10%
C) 50%
D) 5%
  • 13. Which type of star contributes to ionizing hydrogen in the ISM?
A) White dwarfs
B) Neutron stars
C) Red giants
D) OB stars
  • 14. What is the temperature range for the warm neutral medium (WNM)?
A) ~ 104 K
B) O(105 K)
C) < 300 K
D) ~ 106 K
  • 15. What is the approximate number density of air at sea level?
A) ~ 1025 molecules/m3
B) ~ 1012 molecules/m3
C) ~ 100 ions/m3
D) ~ 1016 molecules/m3
  • 16. Which phase of the ISM is shock heated by supernovae?
A) Very hot gas (T ~ 106 K)
B) Photodissociation region
C) Cold dense phase
D) Warm intercloud phase
  • 17. What is the pressure balance condition in the ISM?
A) Pressure varies significantly across different regions.
B) All phases have equal density.
C) Thermal pressure is more important than magnetic fields.
D) The phases are roughly in pressure balance over most of the Galactic disk.
  • 18. Who coined the term 'interstellar'?
A) Edward Barnard
B) René Descartes
C) William Huggins
D) Francis Bacon
  • 19. Which spectral line is most common at millimetre and sub-mm wavelengths in molecular clouds?
A) 21-cm line of H I
B) Forbidden lines of O III
C) Spectral lines from CO
D) Ly-α photon from hydrogen
  • 20. What is the primary source of heavier elements in the ISM?
A) Primordial nucleosynthesis
B) Interstellar dust
C) Stellar nucleosynthesis during stellar evolution.
D) Cosmic rays
  • 21. What happens when dense molecular clouds form stars?
A) They decrease the density of the ISM.
B) They convert surrounding gas into the warm ionized phase, increasing temperature.
C) They reduce the number of hydrogen atoms.
D) They create cold neutral medium.
  • 22. What type of photon emission is associated with fine structure cooling?
A) Bremsstrahlung radiation
B) Inverse Compton scattering
C) Synchrotron radiation
D) Photon emission from de-excitation
  • 23. What type of emission is produced by small grains spinning at GHz frequencies?
A) 21-cm line emission
B) Dipole radiation
C) Far infrared quasi-blackbody emission
D) Millimetre wavelength lines
  • 24. Which molecule's rotational lines are important for cooling in molecular clouds?
A) N II
B) O III
C) H2 (molecular hydrogen)
D) CO (carbon monoxide)
  • 25. What process generates gamma-ray photons when cosmic rays collide with atomic nuclei in ISM clouds?
A) Bremsstrahlung cooling
B) Synchrotron radiation
C) Collision with atomic nuclei
D) Inverse Compton scattering
  • 26. How does the Coriolis force affect large ISM features?
A) It prevents star formation in spiral arms.
B) It influences their dynamics and structure.
C) It compresses all ISM into a thin disk.
D) It has no effect on the ISM.
  • 27. How is the ISM near the center of most galaxies affected?
A) It only contains cold gas.
B) It remains unchanged from the rest of the galaxy.
C) It becomes entirely in the coronal phase.
D) It is profoundly modified by the central supermassive black hole.
  • 28. What type of emission is produced by interstellar dust grains re-emitting absorbed starlight?
A) Synchrotron radiation
B) 21-cm line emission
C) Millimetre wavelength lines
D) Far infrared quasi-blackbody emission
  • 29. What type of emission is produced by interstellar dust grains in the far infrared?
A) Synchrotron radiation
B) Inverse Compton scattering
C) Bremsstrahlung radiation
D) Quasi-blackbody emission
  • 30. What is the estimated mission end date for Voyager 1's study of interstellar plasma and dust?
A) 2020
B) 2025
C) 2030
D) 2040
  • 31. What is used to determine the total amount of dust in front of each star?
A) Reddening
B) Scattering
C) Emission lines
D) Absorption lines
  • 32. What large ionized molecules were detected by Hubble in 2019?
A) Buckminsterfullerene (C60) or 'buckyballs'.
B) Simple hydrocarbons.
C) Carbon monoxide.
D) Only hydrogen and helium molecules.
  • 33. Who confirmed the presence of interstellar dust in 1912?
A) Edward Barnard
B) Slipher
C) Mary Lea Heger
D) Victor Hess
  • 34. What did William Huggins use to determine that a nebula is made of gas?
A) Refraction
B) Photography
C) Telescope lens
D) Spectroscopy
  • 35. Which process bumps up photon energies to X-rays and gamma-rays via cosmic rays?
A) Synchrotron radiation
B) Bremsstrahlung radiation
C) Fine structure cooling
D) Inverse Compton scattering
  • 36. What is the role of photodissociation regions (PDR) in the ISM?
A) They contribute to the heating of the warm neutral medium.
B) They reduce the number of photons with energy below the Lyman limit.
C) They increase the density of molecular clouds.
D) They cool down the ionized gas.
  • 37. Which transition line is strongly absorbed by atomic hydrogen at about 121.5 nanometers?
A) Lyman-alpha transition
B) Brackett-alpha transition
C) Balmer-alpha transition
D) Paschen-alpha transition
  • 38. What type of radiation is believed to be the source of anomalous microwave emission?
A) Dipole radiation from spinning nanometre-sized grains
B) Bremsstrahlung radiation
C) Far infrared quasi-blackbody emission
D) Synchrotron radiation
  • 39. What type of radiation is generated by cosmic-ray electrons spiraling in the galactic magnetic field?
A) Gamma-ray photons
B) Infrared emission
C) Bremsstrahlung radiation
D) Synchrotron radiation
  • 40. In spiral galaxies like the Milky Way, what is the typical scale height of the interstellar medium (ISM)?
A) 500 parsecs
B) 100 parsecs (300 light years)
C) 10,000 parsecs
D) 30,000 parsecs
  • 41. What is the typical orbital speed of gas and stars in the disk of a spiral galaxy?
A) 50 km/s
B) 500 km/s
C) 200 km/s
D) 1000 km/s
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