# Astronomie — Oberstufe (C1/C2) 1: Galactic Astrophysics & Physical Cosmology

> [Deutsch] Astronomie: Advanced galactic dynamics and observational cosmology covering Hubble-Lemaître expansion, the cosmic distance ladder, CMB anisotropies, dark matter halos, dark energy, and cosmic fate.

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- **Markdown URL:** https://flashcards.world/flashcards/sets/a52fe627-df51-45f0-a4f4-7c1fe98b64d2.md
- **Level:** advanced
- **Languages:** de → de
- **Total Cards:** 32

## Flashcards (32 Cards)

| # | Front (Term / Prompt) | Back (Definition / Answer) | Example | Multiple-Choice Options |
| :--- | :--- | :--- | :--- | :--- |
| 1 | What are the leading non-baryonic particle candidates for Cold Dark Matter (CDM)? | • WIMPs (Weakly Interacting Massive Particles): Hypothesized heavy particles (mass ~10–1,000 GeV, e.g., supersymmetric neutralinos) interacting only via gravity and the weak nuclear force. • Axions: Ultra-light pseudo-Nambu-Goldstone bosons (mass ~10⁻⁶ to 10⁻³ eV) originally proposed by Peccei-Quinn to resolve the Strong CP problem in QCD. • Sterile Neutrinos: Heavy right-handed neutrinos with zero weak gauge interactions. • Primordial Black Holes: Sub-stellar black holes formed during the early radiation-dominated era. |  |  |
| 2 | What is Dark Energy and what characterizes the Cosmological Constant (Λ) in Einstein's field equations? | Dark Energy is the unknown, smooth, pervasive component of the universe responsible for cosmic acceleration, possessing negative pressure (P < -ρc²/3). • Cosmological Constant (Λ): Represents invariant vacuum energy of empty spacetime. In the equation of state w = P / (ρ · c²), a cosmological constant has a constant value of w = -1. Because its energy density remains constant as space expands (ρ_Λ = constant), it eventually dominates over diluting matter (ρ_m ∝ a⁻³). |  |  |
| 3 | What observational evidence proved the existence of the supermassive black hole Sagittarius A* at the galactic center? | High-resolution near-infrared adaptive optics (Ghez, Genzel; Nobel Prize 2020) tracked the Keplerian orbits of individual high-velocity 'S-stars' orbiting the Galactic Center over decades. Star S2 completes a 16-year eccentric orbit with a pericenter approach of only 17 light-hours at 7,700 km/s. Applying Newton's/Kepler's laws requires an enclosed dark point-like mass of 4.15 (±0.03) x 10⁶ Solar Masses within that tiny volume, confirmed visually by the Event Horizon Telescope (EHT) shadow image. |  |  |
| 4 | How do Strong Gravitational Lensing and Weak Gravitational Lensing map dark matter distributions? | Mass curves spacetime according to General Relativity, deflecting background light: • Strong Lensing: Massive galaxy clusters bend light from background galaxies into dramatic multiple images, arcs, and Einstein Rings; the separation and geometry allow exact mathematical reconstruction of total cluster mass (dark + baryonic). • Weak Lensing: Subtle, statistical tangential alignment and cosmic shear of millions of background faint galaxies, mapping 3D large-scale dark matter filaments and voids. |  |  |
| 5 | What is the structural difference between Cold Dark Matter (CDM) and Hot Dark Matter (HDM) in cosmic structure formation? | • Cold Dark Matter (CDM): Composed of non-relativistic, slow-moving particles at the epoch of radiation-matter equality. Possesses a tiny free-streaming length, allowing small sub-galactic clumps to collapse first and merge into progressively larger galaxies and clusters ('bottom-up' hierarchical structure formation, matching observations). • Hot Dark Matter (HDM): Composed of relativistic, fast-moving particles (like standard neutrinos) whose large free-streaming scale wipes out small density perturbations, forcing gigantic superclusters to form first ('top-down' fragmentation, ruled out by observation). |  |  |
| 6 | What is Cosmological Redshift (z) and how does it differ fundamentally from a kinematic Doppler shift? | • Kinematic Doppler Shift: Caused by the physical motion of a source through stationary space (special relativity). • Cosmological Redshift (z): Caused by the continuous metric expansion of spacetime itself while photons travel through the cosmos. The wavelength of light is stretched in direct proportion to the cosmic scale factor a(t) between emission and observation: 1 + z = λ_observed / λ_emitted = a_observed / a_emitted = 1 / a(t_emission) Photons are stretched by expanding space, not motion through space. |  |  |
| 7 | What is the modern 'Hubble Tension' in observational cosmology? | A statistically irreconcilable discrepancy (now exceeding 5-sigma significance) between two independent methods of determining H0: 1. Early-Universe CMB method (Planck satellite / ΛCDM model): Yields H0 = 67.4 ± 0.5 (km/s)/Mpc. 2. Late-Universe Local Distance Ladder method (SH0ES team using Gaia parallaxes, Cepheids, and Type Ia supernovae): Yields H0 = 73.0 ± 1.0 (km/s)/Mpc. This discrepancy cannot be explained by known instrumental calibration errors and may indicate new physics beyond standard ΛCDM. |  |  |
| 8 | What are the Friedmann Equations and how does total energy density (Ω) govern the spatial geometry of the universe? | The Friedmann equations relate the expansion rate (H = ȧ/a) to the energy density of the universe: H² = (8πG / 3) · ρ - (k · c² / a²) Dividing by critical density ρ_crit = 3H² / (8πG) defines the density parameter Ω_total = ρ / ρ_crit: • Ω_total = 1 (k = 0): Spatially FLAT Euclidean geometry (sum of triangle angles = 180°). • Ω_total > 1 (k = +1): Spatially CLOSED spherical geometry (finite, unbounded). • Ω_total < 1 (k = -1): Spatially OPEN hyperbolic saddle geometry. |  |  |
| 9 | What are the primary rungs comprising the astronomical Cosmic Distance Ladder? | 1. Trigonometric Parallax (Direct geometric foundation; ESA Gaia spacecraft measuring stellar parallaxes out to ~10 kpc). 2. Standard Candles: Classical Cepheid variable stars (calibrated via the Leavitt Period-Luminosity relation) and Tip of the Red Giant Branch (TRGB) out to ~30–40 Mpc. 3. Type Ia Supernovae: Calibrated using host galaxies containing Cepheids, observable out to billions of parsecs (z > 1). 4. Hubble Flow: Measuring cosmological redshift to determine large-scale cosmic distances. |  |  |
| 10 | What is the Hubble-Lemaître Law and what does the Hubble Constant (H0) quantify? | v = H0 · d • v = Apparent recessional velocity of a distant galaxy (km/s) • d = Proper cosmological distance to the galaxy (Megaparsecs, Mpc) • H0 = The Hubble constant, quantifying the current expansion rate of the universe (units of (km/s)/Mpc). The reciprocal of H0 gives the approximate age scale of the universe (the Hubble Time: t_H = 1 / H0 ≈ 14.4 billion years for H0 ≈ 68 km/s/Mpc). |  |  |
| 11 | What is the 'Cosmological Constant Problem' (Vacuum Catastrophe) in theoretical physics? | Quantum field theory predicts that the vacuum possesses zero-point energy summed across all quantum vibrational modes up to the Planck scale, yielding a theoretical vacuum energy density of ρ_QFT ~ 10¹¹⁴ J/m³. However, the observed cosmological constant density measured by cosmic acceleration is ρ_obs ~ 10⁻⁹ J/m³. This represents a discrepancy of ~120 orders of magnitude (10¹²⁰), considered the worst theoretical prediction in physics. |  |  |
| 12 | What is the Sunyaev-Zel'dovich (SZ) Effect on the Cosmic Microwave Background? | The SZ effect occurs when low-energy CMB photons pass through the hot, ionized intra-cluster gas (ICM, T ~ 10⁷–10⁸ K) of massive galaxy clusters. Thermal electrons inverse-Compton scatter CMB photons, systematically boosting photon energies to higher frequencies. This creates a distinct spectral distortion (a decrease in CMB brightness below ~217 GHz and an increase above it) that allows astronomers to discover distant galaxy clusters independent of redshift. |  |  |
| 13 | What cosmological parameters are determined by the first, second, and third acoustic peaks in the CMB angular power spectrum? | Acoustic oscillations represent sound waves propagating through the coupled photon-baryon fluid before decoupling: • 1st Acoustic Peak (angular multipole l ≈ 220, ~1°): Determines total spatial curvature Ω_total, proving the universe is spatially flat (Ω ≈ 1.00 ± 0.002). • 2nd Acoustic Peak: Governs baryon-to-photon ratio, accurately measuring baryonic matter density (Ω_b ≈ 0.049). • 3rd Acoustic Peak: Measures the gravitational potential well depths, determining Cold Dark Matter density (Ω_c ≈ 0.26). |  |  |
| 14 | How did Vera Rubin and Kent Ford's galaxy rotation curves provide decisive proof of galactic dark matter halos? | Classically, according to Keplerian dynamics (v = sqrt(G·M/r)), rotational speeds of stars and gas in spiral galaxies were expected to decline at large radii beyond the luminous optical disk (v ∝ r^(-1/2)). Instead, Rubin and Ford's spectroscopic measurements revealed flat rotation curves (v(r) ≈ constant) extending far beyond visible starlight, proving spiral galaxies are embedded within massive, extended spherical halos of invisible Dark Matter. |  |  |
| 15 | What are the primary anatomical components of the Milky Way galaxy? | 1. Thin Disk: Scale height ~300 pc, diameter ~30 kpc; contains gas, dust, open clusters, and young Population I stars. 2. Thick Disk: Scale height ~1,000 pc; older intermediate-metallicity stars. 3. Central Bulge: Dense spheroidal concentration of Population II stars and a stellar bar (~1–2 kpc radius). 4. Stellar Halo: Diffuse sphere extending to ~50 kpc; contains ancient metal-poor Population II stars and ~150 Globular Clusters. 5. Dark Matter Halo: Massive spherical halo extending to >200–300 kpc, comprising ~90% of total galaxy mass. |  |  |
| 16 | What is the Unified Model of Active Galactic Nuclei (AGN) and how does it explain quasars, Seyfert galaxies, and blazars? | All AGN are powered by a central Supermassive Black Hole (SMBH, 10⁶–10¹⁰ M_sun) accreting gas from a glowing accretion disk, surrounded by an obscuring dusty molecular torus and launching collimated relativistic jets. Observational classifications depend strictly on viewing orientation: • Blazars: Looking directly down the relativistic jet beam (extreme Doppler beaming). • Quasars / Seyfert 1: Looking into the central broad-line region above/inside the torus. • Seyfert 2 / Radio Galaxies: Looking edge-on through the opaque molecular torus (broad lines obscured, only narrow lines visible). |  |  |
| 17 | What is the measured temperature of the CMB today and how closely does it match an ideal blackbody spectrum? | The CMB has an average temperature today of exactly T0 = 2.72548 (±0.00057) Kelvin. In 1990, the FIRAS instrument on the COBE satellite measured the CMB spectrum and found it matches a theoretical Planck blackbody radiation curve with deviations smaller than 50 parts per million (< 0.005%) across all frequencies, making it the most perfect blackbody spectrum known in nature. |  |  |
| 18 | What is Quintessence and how does it differ from a static cosmological constant? | Quintessence is a dynamical, time-evolving scalar field (φ) with a self-interacting potential V(φ) proposed as an alternative to a cosmological constant. Unlike a static constant where w = -1 always, quintessence features a dynamic equation of state w(t) that can change over cosmic time (typically -1 < w < -1/3), which can be tested observationally by measuring whether w departs from exactly -1. |  |  |
| 19 | What did the 1998 High-Z Supernova Search Team and Supernova Cosmology Project discover using Type Ia supernovae? | By measuring apparent luminosities and redshifts of distant Type Ia supernovae (Perlmutter, Schmidt, Riess; Nobel Prize 2011), both teams discovered that distant supernovae were significantly fainter (farther away) than predicted for any matter-dominated decelerating universe. This proved that the cosmic expansion rate of the universe is not slowing down under gravity, but has been accelerating for the past ~5–6 billion years. |  |  |
| 20 | What are the CMB primary temperature anisotropies (ΔT / T ~ 10⁻⁵) and what did they seed in the universe? | Tiny directional temperature fluctuations on the order of 1 part in 100,000 (~30 microKelvin) superimposed on the uniform 2.725 K background. These temperature anisotropies correspond directly to primordial baryonic/dark matter density perturbations seeded by quantum fluctuations stretched during Cosmic Inflation, which subsequently collapsed under gravity over 13.8 billion years to form all galaxies, clusters, and cosmic web filaments. |  |  |
| 21 | What are the primary galaxy morphological classes in the Hubble Tuning Fork classification? | • Elliptical Galaxies (E0 to E7): Smooth, featureless, spheroidal ellipsoids lacking disks or dust lanes; E0 is spherical, E7 is highly elongated; dominated by old Population II stars. • Lenticular Galaxies (S0 / SB0): Intermediate disk galaxies possessing a central bulge and disk but lacking spiral arm structure. • Normal Spirals (Sa, Sb, Sc): Disks with prominent spiral arms; Sa has large bulge and tight arms, Sc has small bulge and open loosely wound arms. • Barred Spirals (SBa, SBb, SBc): Spirals with a central linear bar of stars traversing the nucleus. • Irregular Galaxies (Irr I, Irr II): Asymmetrical, chaotic systems rich in gas and active star formation. |  |  |
| 22 | What was the Cosmic Epoch of Reionization and what astronomical sources brought about its occurrence? | Between z ≈ 20 and z ≈ 6 (~150 to 1,000 million years after Big Bang), the neutral hydrogen gas filling the intergalactic medium (IGM) was re-ionized into free protons and electrons. This was caused by intense Lyman continuum ultraviolet radiation emitted by the first generation of massive, metal-free stars (Population III stars) and early accreting supermassive black holes (quasars), ending the cosmic 'Dark Ages'. |  |  |
| 23 | How did Fritz Zwicky deduce the existence of Dark Matter in the Coma Cluster in 1933? | Zwicky measured the radial velocities of individual galaxies in the Coma Cluster using optical Doppler shifts and applied the Virial Theorem (2<K> + <U> = 0). The observed high velocity dispersion (~1,000 km/s) required roughly 400 times more total gravitational mass to hold the cluster together than could be accounted for by the visible light of the stars, leading Zwicky to postulate an invisible 'dunkle Materie' (dark matter). |  |  |
| 24 | What is the Cosmic Microwave Background (CMB) and what epoch in early cosmic history does it originate from? | The CMB is the thermal relic radiation from the Recombination and Photon Decoupling Epoch (~380,000 years after the Big Bang, at redshift z ≈ 1,100). As the expanding primordial universe cooled below ~3,000 K, free electrons bound with protons and helium nuclei to form neutral atoms. Photons ceased Thomson scattering off free electrons, allowing light to decouple and stream freely through the transparent cosmos. |  |  |
| 25 | What is the modern cosmic energy-matter budget according to the standard ΛCDM cosmological model? | As determined by Planck CMB data and large-scale galaxy surveys: • Dark Energy (Λ): ~68.3% of total cosmic energy density • Cold Dark Matter (CDM): ~26.8% of total energy density • Baryonic Matter (atoms, stars, gas, planets, humans): ~4.9% of total energy density • Relativistic Radiation and Neutrinos: < 0.1% today |  |  |
| 26 | What is the Friedmann-Lemaître-Robertson-Walker (FLRW) metric and what does the cosmic scale factor a(t) represent? | The FLRW metric is the exact general relativistic metric solution describing a homogeneous and isotropic expanding (or contracting) universe: ds² = c² dt² - a(t)² · [dr²/(1 - k·r²) + r²(dθ² + sin²θ dφ²)] • a(t) = Dimensionless cosmic scale factor parameterizing how spatial physical distances expand as a function of cosmic time t (normalized to a(t_today) = 1). • k = Geometric spatial curvature constant (k = +1 spherical closed, k = 0 flat Euclidean, k = -1 hyperbolic open). |  |  |
| 27 | Why is the colliding 'Bullet Cluster' (1E 0657-56) considered definitive empirical proof of dark matter over Modified Newtonian Dynamics (MOND)? | In the high-speed collision of two galaxy clusters, the hot X-ray-emitting baryonic plasma gas (making up ~90% of baryonic mass) collided and stalled in the center due to electromagnetic fluid drag (ram pressure). In contrast, stars and collisionless dark matter passed straight through without drag. Weak lensing mass reconstructions show the gravitational mass peaks coincide with the collisionless galaxies, NOT with the baryonic gas, proving dark matter exists as physical mass independent of modified gravity. |  |  |
| 28 | What is Cosmic Inflation and what major cosmological problems does it resolve? | Proposed by Alan Guth and Andrei Linde (1981), Cosmic Inflation is a period of exponential spatial expansion driven by a scalar field ('inflaton') in the first ~10⁻³⁶ to 10⁻³² seconds after the Big Bang (expanding space by a factor of >10²⁶). Resolves: 1. Horizon Problem: Explains why opposite sides of the universe have identical CMB temperatures by placing them in causal thermal contact prior to inflation. 2. Flatness Problem: Explains why space is flat by dynamically driving Ω toward 1. 3. Magnetic Monopole Problem: Dilutes unobserved topological defects to imperceptible densities. |  |  |
| 29 | What is the Tully-Fisher relation and what does it relate in spiral galaxies? | The Tully-Fisher relation is an empirical power-law relationship for spiral galaxies linking their intrinsic total luminosity (L) to their maximum asymptotic rotational velocity (v_max, measured via Doppler broadening of the 21-cm neutral hydrogen HI line): L ∝ (v_max)⁴ Because rotation speed depends on total gravitational mass, measuring HI line width determines intrinsic luminosity, providing a standard candle to calculate galactic distance via the distance modulus. |  |  |
| 30 | What physical processes occur when two large spiral galaxies collide and merge? | Stars are so widely separated that individual stars almost never collide directly. However, interstellar gas clouds collide, compress, and undergo shocks, triggering colossal starbursts of rapid star formation. Gravitational tidal forces stretch long tidal tails of stars and gas. Dynamical friction converts orbital kinetic energy into heat, randomizing stellar orbits and disrupting thin disks, typically transforming two gas-rich spirals into a single giant elliptical galaxy. |  |  |
| 31 | What are the three primary potential ultimate fates of our universe: Big Freeze, Big Rip, and Big Crunch? | • Big Freeze (Heat Death): Standard ΛCDM outcome (w = -1); eternal expansion dilutes matter; star formation ceases in ~10¹⁴ years; white dwarfs and neutron stars cool; supermassive black holes evaporate via Hawking radiation (~10¹⁰⁰ years); universe reaches maximum entropy. • Big Rip: Occurs if dark energy is phantom energy (w < -1); dark energy density accelerates toward infinity, systematically tearing apart galaxy clusters, galaxies, planetary orbits, atoms, and spacetime itself in a finite time. • Big Crunch: Occurs if spatial curvature is closed (k = +1) or dark energy decays into negative potential energy; expansion reverses and the cosmos collapses back into a universal singularity. |  |  |
| 32 | What is the Faber-Jackson relation in elliptical galaxies? | The Faber-Jackson relation is an empirical scaling relationship for elliptical galaxies connecting their intrinsic luminosity (L) to the central stellar velocity dispersion (σ, the random velocity spread of stars along the line of sight measured from spectral absorption line widths): L ∝ σ⁴ It is the elliptical galaxy counterpart to the Tully-Fisher relation, forming a 2D projection of the more fundamental 3D 'Fundamental Plane' (which includes effective radius R_e). |  |  |

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