Questions and Answers
Describe several characteristics that distinguish Population I stars from Population II stars.
Population I stars are luminous, hot, young, and concentrated in the disk of spiral galaxies. Population II stars are older, less luminous, and cooler.
Briefly describe the main parts of our Galaxy.
The Galaxy consists of a thin, circular, rotating disk, a central bulge, and a spherical halo with globular clusters.
Which kind of objects occur only in spiral arms?
Which of the following objects are thought to be very old?
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Why does star formation occur primarily in the disk of the Galaxy?
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How would the appearance of the Galaxy be different if stars evolved without losing mass?
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Which galaxy has more older stars, a spiral or an elliptical galaxy?
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What are the two best ways to measure the distance to a distant, isolated spiral galaxy?
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What does it mean to say that the universe is expanding?
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Is the Hubble constant actually constant?
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Which is redder, a spiral galaxy or an elliptical galaxy?
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Describe some differences between quasars and normal galaxies.
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Describe the process by which a black hole can explain the energy radiated by quasars.
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Why do astronomers believe that quasars represent an early stage in the evolution of galaxies?
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How are distant (young) galaxies different from the galaxies that we see in the universe today?
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Would the acceleration of the universe occur if it were composed entirely of matter?
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What is the evidence that a large fraction of the matter in the universe is invisible?
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Describe some possible futures for the universe that scientists have come up with.
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Which formed first: hydrogen nuclei or hydrogen atoms?
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Study Notes
Population I vs Population II Stars
- Population I stars are brighter, hotter, younger, and found mainly in spiral galaxies' disks.
- Population II stars are older, cooler, and less luminous, typically found in globular clusters and galaxy nuclei.
Main Parts of Our Galaxy
- The galaxy features a thin, rotating disk with a concentration of young stars, gas, and dust.
- Central bulge made up of older stars; spiral arms contain star formation activity.
- Embedded in a spherical halo filled with globular clusters.
Galactic Objects and Their Locations
- Open clusters, giant molecular clouds, and group of O and B stars exist primarily in spiral arms.
- Globular clusters found in non-spiral arm regions and consist of older stars.
- Young objects include group of O and B stars and giant molecular clouds.
Star Formation in the Galaxy
- Star formation predominantly occurs in the galaxy's disk due to density waves compressing gas and dust.
Hypothetical Mass Loss Scenarios
- Without mass loss, the Milky Way could potentially consist of around 100 billion stars, influencing its appearance.
Types of Galaxies
- Spiral galaxies: characterized by spiral shapes, with a halo, bulge, and flat disk.
- Elliptical galaxies: elliptical or spherical shape, with predominantly older stars.
- Irregular galaxies: no defined shape due to irregular gravitational forces.
Measuring Distances to Galaxies
- Type Ia supernovae allow calculation of distance by comparing luminosity and apparent brightness.
- Tully-Fisher relation utilizes 21-cm radiation for measuring rotational rate and determining distance.
Expanding Universe
- Expansion refers to galaxies moving away from each other; local systems like the solar system remain stable due to gravitational binding.
Hubble Constant
- The Hubble constant is constant in space but varies over time and is not truly constant.
Color Comparison of Galaxies
- Elliptical galaxies appear redder due to the predominance of older stars which emit light in redder wavelengths.
Spectral Line Broadness in Elliptical Galaxies
- Broader spectrum lines indicate higher velocities of constituent stars within the galaxy.
Quasars vs Normal Galaxies
- Quasars, appearing at large redshifts, are significantly brighter and contain a single black hole, while normal galaxies harbor millions of stars.
Quasars Distance Arguments
- No blue-shifted quasars found, indicating they are not gravitationally bound and support their distant status.
Energy from Black Holes in Quasars
- Hot accretion disks form as materials fall into black holes, radiating energy across the electromagnetic spectrum.
Quasars and Galaxy Evolution
- Decrease in observable quasars implies they represent an early evolutionary stage of galaxies.
Black Holes and Energy Emission
- Black holes attract matter, which accelerates outside the event horizon, leading to intense energy emission during the fall.
Characteristics of Distant Galaxies
- Distant young galaxies exhibit lower luminosity and higher gas content compared to current galaxies.
Universe Homogeneity and Isotropy
- Universe appears uniform and consistent in all directions; distribution of elephants on Earth is not homogeneous or isotropic.
Invisible Matter Evidence
- Galactic dynamics indicate a need for dark matter, as gravitational forces exceed observable matter.
Supercluster Arrangement
- Superclusters are structured in filaments and sheets, interspersed with voids on large cosmic scales.
Galaxy Evolutionary Pathways
- Spiral galaxies rotate rapidly; elliptical galaxies do not evolve into spirals due to absence of rotation mechanisms.
Light Travel from Stars
- Stars emitting light observed after 10,000 years are within the Milky Way, as its diameter is around 100,000 light years.
Cosmology Theories
- Must explain universe's expansion, inflation, cosmic microwave background, and elemental abundance (e.g., helium).
Possible Future of the Universe
- Future trajectories depend on expansion dynamics, with possible outcomes including perpetual expansion or a "big crunch."
Formation of Hydrogen Nuclei vs Atoms
- Hydrogen nuclei formed within seconds post-Big Bang; hydrogen atoms formed 380,000 years later when conditions were favorable for atom formation.
Big Bang and Helium Abundance
- The Big Bang model accounts for helium production through early nucleosynthesis processes, explaining its abundance beyond stellar production.
Evidence for Accelerating Expansion
- Observations of distant supernovae reveal fainter appearances than expected, indicating the universe's expansion rate is increasing.
Matter-Only Universe Dynamics
- A universe composed solely of matter would decelerate expansion due to gravity, not accelerate it.
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Description
Test your knowledge of key concepts in astronomy with these flashcards. This set focuses on distinguishing between Population I and Population II stars as well as the main parts of our Galaxy. Perfect for exam preparation!
