ASP Galaxies and Cosmology 1 — Questions and Answers
Question 1: What is the Hubble classification system for galaxies?
- A system based on galaxy size
- A morphological classification dividing galaxies into ellipticals, spirals, and irregulars (Correct answer)
- A system based on galaxy luminosity
- A classification based on galaxy age
Correct answer: A morphological classification dividing galaxies into ellipticals, spirals, and irregulars
The Hubble tuning fork diagram classifies galaxies morphologically into ellipticals (E0-E7), lenticulars (S0), spirals (Sa-Sc), barred spirals (SBa-SBc), and irregulars.
Question 2: What is the cosmic microwave background (CMB) radiation?
- Radiation emitted by active galactic nuclei
- The afterglow of the Big Bang permeating all of space (Correct answer)
- Radiation from the sum of all stars in the observable universe
- Gamma radiation from neutron star mergers
Correct answer: The afterglow of the Big Bang permeating all of space
The CMB is the thermal radiation left over from the early universe about 380,000 years after the Big Bang, now cooled to approximately 2.73 Kelvin and permeating all of space uniformly.
Question 3: What is Hubble's Law?
- The rule that stars on the main sequence follow a mass-luminosity relationship
- The relationship showing that galaxies recede from us at a velocity proportional to their distance (Correct answer)
- The classification system for galaxies based on morphology
- The principle that all galaxies have supermassive black holes
Correct answer: The relationship showing that galaxies recede from us at a velocity proportional to their distance
Hubble's Law states that distant galaxies recede from us with velocities proportional to their distances (v = H₀ × d), providing evidence for the expanding universe.
Question 4: What is dark matter?
- Matter composed of very cold gas clouds
- Matter that does not emit or absorb light but exerts gravitational effects (Correct answer)
- Black holes distributed throughout galaxies
- The matter inside stellar cores
Correct answer: Matter that does not emit or absorb light but exerts gravitational effects
Dark matter is an unseen form of matter that does not interact electromagnetically (neither emitting nor absorbing light) but whose gravitational effects are evident in galaxy rotation curves and cosmic structure.
Question 5: What is a quasar?
- A quasi-periodic oscillating star
- An extremely luminous active galactic nucleus powered by a supermassive black hole (Correct answer)
- A failed galaxy that never formed stars
- A type of neutron star emitting radio waves
Correct answer: An extremely luminous active galactic nucleus powered by a supermassive black hole
A quasar (quasi-stellar object) is an extremely luminous active galactic nucleus powered by material accreting onto a supermassive black hole, often outshining entire galaxies.
Question 6: What is the Local Group of galaxies?
- The cluster of galaxies closest to the Milky Way's center
- The group of approximately 80 galaxies that includes the Milky Way and Andromeda (Correct answer)
- A cluster of quasars in the nearby universe
- The group of star-forming regions in our galaxy
Correct answer: The group of approximately 80 galaxies that includes the Milky Way and Andromeda
The Local Group is the galaxy group that includes the Milky Way, Andromeda (M31), Triangulum (M33), and about 80 smaller dwarf galaxies, spanning roughly 10 million light-years.
ASP Galaxies and Cosmology 1
What is the Hubble classification system for galaxies?