Exercises

-> HS2026_tasks

Vorlesung

4. Stellar Evolution

#timestamp 2026-09-21

• Mass-Luminosity Trade-off: More massive stars burn hydrogen faster and die much sooner.
  • $1M_{\odot }\approx {10}^{10}\text{ years}$
  • $15M_{\odot }\approx {10}^7\text{ years}$
• Nuclear Fusion: Core hydrogen fuses into helium via the $p\text{-}p$ chain (low mass) or CNO cycle (high mass).

Low to Intermediate Stars ($M<8M_{\odot }$)
-> Evolution: Main Sequence $\to$ Red Giant (RGB) $\to$ Horizontal Branch $\to$ Asymptotic Giant (AGB) $\to$ Planetary Nebula $\to$ White Dwarf

• Helium Flash: Stars below $\approx 2M_{\odot }$ develop a degenerate helium core. Core helium ignition occurs explosively once temperatures rise enough.
• Final Remnant: Planetary nebula ejects the outer layers, leaving behind a Carbon-Oxygen White Dwarf held up by electron degeneracy pressure.

Massive Stars ($M>8M_{\odot }$)
-> Evolution: Main Sequence $\to$ Supergiant $\to$ Onion-Skin Shell Burning $\to$ Core-Collapse Supernova $\to$ Neutron Star / Black Hole

• Onion-Skin Burning: Successive core/shell burning stages grow shorter and hotter:
  $\text{H}\to \text{He}\to \text{C}\to \text{Ne}\to \text{O}\to \text{Si}\to \text{Fe}$
• The Iron Boundary: Fusing Iron ($\text{Fe}$) absorbs energy rather than releasing it.
• Core Collapse: When the iron core reaches the Chandrasekhar limit ($\approx 1.4M_{\odot }$):

1. Photodisintegration breaks iron nuclei.
2. Electron capture ($p+e^{-}\to n+{\nu }_e$) neutralizes protons.
3. Outer layers collapse onto the dense core, bounce off, and trigger a Type II Supernova.

• White Dwarf: Supported by electron degeneracy pressure ($M_{\text{core}}<1.4M_{\odot }$).
• Neutron Star: Supported by neutron degeneracy pressure ($1.4M_{\odot }<M_{\text{remnant}}<3M_{\odot }$).
• Black Hole: TOV limit exceeded; gravity overwhelms all degeneracy pressure ($M_{\text{remnant}}>3M_{\odot }$).

5. Galactic structure

• Central bulge, bar: Central, rounder galaxy region. Ranges from a spherical "classical" bulge to a flattened "pseudo-bulge" or bar. dominates galactic dynamics within a few $kpc$ of the center. Surface-brightness profile well represented by a Sérsic profile
• Galactic Disk: A flattened structure extending radially from the center containing stars and gas. Its radial light distribution generally follows an exponential profile

• Stellar Halo: A surrounding structure containing stars and globular clusters. Contains relatively little mass (e.g., $\sim {10}^9{M}_{\odot }$ in the Milky Way), but acts as a tracer population where dark matter dominates
• Dark Matter Halo: A vast, surrounding halo of dark matter that dominates the total mass profile and dynamics of the galaxy at larger radial distances ($r$).

6. Active Galactic Nuclei (AGN)

-> main point: different classes of AGNs are fundamentally the same physical system viewed from different angles/having varying jet activity

components

• Central Supermassive Black Hole (SMBH): A black hole with, ${10}^6<m<{10}^{10}{M}_{\odot }$, drives the system via matter accretion
• Broad-Line Region (BLR): Fast-moving gas clouds close to black hole ($D\approx 0.1\text{--}1\text{ pc}$), emitting broad emission lines due to high-velocity orbital motion
• Narrow-Line Region (NLR): Slower-moving gas clouds located further out from the central engine -> narrower emission lines
• Dusty Torus: A doughnut-shaped ring of thick dust and gas surrounding the inner regions (accretion disk and BLR). Depending on the line of sight, this torus obscures the central engine and BLR
• Relativistic Jets: Collimated outflows launched perpendicularly to the accretion disk.

The unified model posits that different observed classes of Active Galactic Nuclei (AGN) are fundamentally the same physical system viewed from different angles or possessing varying degrees of jet activity.

• BL Lac = blazars
• OVV = optically violently variable
• BLRG = broad-line radio galaxy
• NLRG = narrow-line radio galaxy
• Sey 1= Seyfert type 1 (broad emission lines visible)
• Sey 2 = Seyfert type 2 (only narrow emission lines visible)

7. EXTRA: EBL

Extragalactic Background Light (EBL) is the accumulated diffuse radiation emitted throughout the history of the Universe by extragalactic sources, primarily driven by star formation (nucleosynthesis) and active galactic nuclei / black holes (gravitation). Total EBL is equivalent to $\approx 5\mathrm{\%}$ of the Cosmic Microwave Background (CMB)

• Absolute EBL/CIB measurements are difficult due to local foregrounds like zodiacal light and Galactic dust/cirrus

8.

Übungen