Quarks to Cosmos All Lecture Sheets

Midterm 2

What is Hubble’s Law?

v = H₀ d.

What determines expansion rate?

Energy density (matter, radiation, dark energy).

Does H₀ change?

Yes over cosmic time.

Can expansion exceed c?

Yes; space expands.

What does z > 1 indicate?

Large redshift; very distant.

Most distant standard candles?

Type Ia supernovae.

Einstein’s “biggest mistake”?

Cosmological constant for static universe.

Consequence of expansion?

Universe is dynamic, not static.

What is a spiral nebula?

Old word for galaxy.

Herschel’s model?

Milky Way map via star counts.

Cepheid variable?

Pulsating star with period-luminosity law.

How to calibrate Cepheids?

Distances to nearby Cepheids.

Who proposed dark matter?

Zwicky.

Who confirmed via rotation curves?

Vera Rubin.

Three DM evidence lines?

Rotation curves, lensing, cluster dynamics.

Bullet Cluster?

Shows DM separated from gas after collision.

Why DM isn’t ordinary matter?

Doesn’t emit/absorb/scatter light.

MACHO vs WIMP?

MACHO = compact; WIMP = particle.

What happens when neutron degeneracy fails?

Collapse to a black hole.

What is the Schwarzschild radius?

Radius of event horizon.

Schwarzschild radius of Earth & Sun?

Earth ~9 mm; Sun ~3 km.

What is gravitational redshift?

Light loses energy escaping gravity → redshift.

What do we see as object falls in?

Appears to freeze and redshift at horizon.

Cygnus X-1?

First strong stellar black-hole candidate.

What is LIGO?

Gravitational wave detector.

GW170817?

First neutron star merger detected in gravitational waves.

If Jupiter becomes BH, what changes?

Nothing about orbits; same mass → same gravity.

Types of black holes?

Stellar, Intermediate, Supermassive.

Sgr A*?

Supermassive black hole at Milky Way center.

What is an LGM?"Little Green Men” nickname for first pulsars.

Why do pulsars pulse?

Rotating beams from magnetic poles.

What is a millisecond pulsar?

Fast “recycled” pulsar.

Mass required for pulsar formation?>8 solar masses originally.

What prevents NS collapse?

Neutron degeneracy pressure.

Max NS mass?~2–3 solar masses.

Escape velocity of Earth?~11 km/s.

Escape velocity of neutron star?~0.3c.

What is a GRB?

Gamma-ray burst.

Why GRBs confusing initially?

Unknown distance; huge energy.

Accretion disk?

Rotating infalling material.

Kilonova?

Short-lived EM burst from neutron star merger.

Collapsar?

Massive star collapsing to black hole.

What is needed for a nova?

White dwarf + mass transfer.

What is a Roche lobe?

Region where a star’s gravity dominates; overflow → accretion.

Chandrasekhar limit?~1.4 solar masses.

What happens if a white dwarf exceeds it?

Type Ia supernova.

Heavy vs light star evolution?

Heavy: fuse to iron; light: stop at C/O (limit ~8 solar masses).

What accumulates in heavy star cores?

Iron.

Nova vs supernova?

Nova = surface explosion; supernova = catastrophic collapse.

Type I vs Type II supernova?

Type I: no H lines; Type II: hydrogen present.

What stops core collapse supernova?

Neutron degeneracy pressure.

Most stable element?

Iron-56.

Alpha, beta, neutron decay?

Alpha = He nucleus; Beta = n ↔ p + e ± ν; Neutron = free neutron emitted.

s-process?

Slow neutron capture; stops at Pb; AGB stars.

r-process?

Rapid neutron capture; creates very heavy elements; mergers & supernovae.

Remnants of Type Ia and Type II?

Type Ia: none; Type II: neutron star or black hole.

Neutron star properties?~10 km radius, 1.4–2 M☉, ~10^17 kg/m³.

What is the Standard Model?

Theory of fundamental particles and forces (except gravity).

How many generations of matter?

Three; differ in mass and stability.

Force carriers?

Photon, W/Z, gluon, Higgs.

Difference between quarks and leptons?

Quarks feel strong force; leptons do not.

What is a neutrino?

Neutral, tiny mass, interacts only via weak force.

What makes an electron neutrino?

Created with electrons in weak interactions.

Solar neutrino problem?

Too few detected neutrinos; solved by oscillations.

Experiment that solved it?

SNO (Sudbury Neutrino Observatory).

What balances hydrostatic equilibrium on the main sequence?

Gravity vs fusion pressure.

What element accumulates in the Sun's core during the main sequence?

Helium.

Does a solar-mass star stay the same during the main sequence?

No; it brightens and expands.

What happens as the Sun leaves the main sequence?

Core contracts, outer layers expand → red giant.

Appearance in red giant phase?

Bigger, cooler, redder, more luminous.

What is the helium flash?

Sudden He fusion in a degenerate core.

Why doesn’t the core expand during the helium flash?

Electron degeneracy pressure.

Triple-alpha process?

3 He → C.

What builds up during He burning?

Carbon and oxygen.

End of AGB phase produces?

Planetary nebula + white dwarf.

What stabilizes a white dwarf?

Electron degeneracy pressure.

What process heavy stars undergo that Sun will not?

Fusion to iron and core collapse (>8 solar masses).

What are the stellar spectral classes and what does the order mean?

O, B, A, F, G, K, M. Ordered by decreasing temperature. Originally alphabetical by spectral line strength.

What is the Sun’s spectral class?

G2V.

Where are red giants, main sequence, and white dwarfs on the HR diagram?

Red giants = upper right; Main sequence = diagonal; White dwarfs = lower left.

What determines if a star is on the main sequence?

Hydrogen fusion in the core.

How does luminosity depend on mass?

L ∝ M^3–4.

How does lifetime depend on mass?

Lifetime ∝ 1 / M^2.5.

What are the regions of the Sun?

Core, Radiative zone, Convective zone, Photosphere, Chromosphere, Corona.

What is hydrostatic equilibrium?

Gravity inward balanced by pressure outward.

What powers the Sun?

Proton-proton chain: H → He + energy. E = mc².

Other products of the pp-chain?

Neutrinos.

How many solar neutrinos reach Earth?~10^38 per second.

Mass lost by Sun per second?~4 × 10^9 kg/s.

Age of the Sun?~4.6 billion years.