Astrophysics, Cosmology & Relativity

Gravitational Lensing

The bending of light rays from a background astronomical source around a massive foreground object acting as a gravitational lens.

θ_deflection = (4 G M) / (c² b) Arcseconds (Angular Deflection)

Gravitational Time Dilation

The phenomenon where time passes measurably slower in regions of lower gravitational potential (stronger gravity).

t_0 = t_f √(1 - 2 G M / (r c²)) Seconds (Relativistic Time Difference)

Astrophysics, Cosmology & Relativity

Gravitational Waves

Ripples in the curvature of spacetime that propagate outward as transverse waves at the speed of light, generated by accelerating…

h_ij = (2 G / (c⁴ r)) (d²I_ij / dt²), Strain h = ΔL / L ~ 10⁻²¹ Dimensionless Strain h (10⁻²¹)

Astrophysics, Cosmology & Relativity

Great Attractor

A massive gravitational anomaly in intergalactic space at the center of the Laniakea Supercluster pulling galaxies across hundreds of…

v_peculiar ~ 600 km/s towards Laniakea Supercluster center M_☉ (Gravitational Anomaly Mass)

Astrophysics, Cosmology & Relativity

Hawking Radiation

Thermal blackbody radiation predicted to be emitted by black holes due to quantum field fluctuations near the event horizon.

T_H = ℏ c³ / (8 π G M k_B), P = ℏ c⁶ / (15360 π G² M²) Kelvin (Blackbody Temperature T_H)

Astrophysics, Cosmology & Relativity

Hertzsprung-Russell (H-R) Diagram

A foundational scatter plot of stellar luminosity versus surface temperature (or spectral type) used to trace stellar evolution phases.

L ∝ R² T^4 (Plot of Absolute Magnitude vs Spectral Type) Luminosity (L_☉) vs Surface Temp (K)

Astrophysics, Cosmology & Relativity

Hubble's Law

The cosmological observation that galaxies recede from Earth at velocities directly proportional to their proper distance.

v = H₀ d, H₀ ≈ 70 (km/s) / Mpc km/s/Mpc (Hubble Constant)

Astrophysics, Cosmology & Relativity

Length Contraction

The relativistic effect where an object's length in the direction of motion is measured shorter by a stationary observer than its proper…

L = L₀ / γ = L₀ √(1 - v²/c²) Meters (Spatial Length)

Astrophysics, Cosmology & Relativity

Light Year

An astronomical unit of length equal to the distance light travels in a vacuum in one Julian year (365.25 days).

1 ly = c × 1 year ≈ 9.461 × 10¹⁵ m ≈ 63,241 AU Light-Years (ly)

Astrophysics, Cosmology & Relativity

Local Group

The small galaxy cluster group comprising the Milky Way, Andromeda (M31), Triangulum (M33), and over 80 dwarf satellite galaxies.

Diameter ~ 3 Mpc (~10 million ly), Mass ~ 2 × 10¹² M_☉ Megaparsecs (Mpc)

Astrophysics, Cosmology & Relativity

Lorentz Factor

The fundamental relativistic factor by which time dilation, length contraction, and relativistic mass scale for objects moving at velocity…

γ = 1 / √(1 - v²/c²) = 1 / √(1 - β²) Dimensionless Factor (γ ≥ 1)

Astrophysics, Cosmology & Relativity

Main Sequence

The continuous evolutionary diagonal band on the Hertzsprung-Russell diagram containing stars fusing hydrogen into helium in their cores.

L ∝ M^3.5 (Mass-Luminosity Relation) H-R Diagram Band

Astrophysics, Cosmology & Relativity

Mass-Energy Equivalence

The fundamental relativistic principle stating that mass and energy are directly proportional and interchangeable physical quantities.

E = m c² = γ m₀ c² Joules or MeV / GeV

Astrophysics, Cosmology & Relativity

Minkowski Space

The flat four-dimensional spacetime manifold combining 3D Euclidean space and time used to formulate Special Relativity.

ds² = -c² dt² + dx² + dy² + dz² Flat 4D Spacetime Metric

Astrophysics, Cosmology & Relativity

Multiverse

A hypothetical set of multiple co-existing universes that together comprise all of physical reality.

Cosmic Inflation Bubble Universes & Many-Worlds Everett Branching Cosmological Hypothesis

Astrophysics, Cosmology & Relativity

Nebula

An interstellar cloud of dust, hydrogen, helium, and ionized gases in space, serving as a site for star formation.

M_Jeans = (5 k_B T / (G μ m_H))^(3/2) (3 / (4 π ρ))^(1/2) Light-Years (Diameter)

Astrophysics, Cosmology & Relativity

Neutron Star

An ultradense stellar core remnant produced by the core-collapse supernova explosion of a massive star, composed almost entirely of…

M ≈ 1.4–2.1 M_☉, R ≈ 10–12 km, ρ ≈ 10¹⁷ kg/m³ M_☉ (Mass), km (Radius)

Astrophysics, Cosmology & Relativity

Olbers' Paradox

The apparent paradox that if the universe were static, infinite, and uniformly populated with stars, the night sky should be uniformly…

Night sky brightness J = ∫ 4 π I r² dr / (4 π r²) → ∞ (in static infinite universe) Cosmological Paradox

Astrophysics, Cosmology & Relativity

Parsec

An astronomical unit of distance equal to the distance at which a star exhibits a trigonometric parallax angle of exactly one arcsecond…

1 pc = 1 AU / tan(1″) ≈ 3.2616 ly ≈ 3.0857 × 10¹⁶ m Parsecs (pc, kpc, Mpc)

Astrophysics, Cosmology & Relativity

Proper Time

The physical time interval measured by a clock moving along a specific worldline through spacetime.

dτ = dt / γ = √(dt² - dx²/c²) Seconds (Proper Time τ)

Astrophysics, Cosmology & Relativity

Protostar

An early evolutionary mass phase of a star formed by the gravitational contraction of an interstellar gas cloud before core hydrogen fusion…

t_collapse ~ t_freefall = √(3π / (32 G ρ)) Solar Masses & Years

Astrophysics, Cosmology & Relativity

Pulsar

A highly magnetized, rapidly rotating neutron star that emits focused beams of electromagnetic radiation from its magnetic poles.

P_spin ~ 1.4 ms to 10 s, P_dot = dP / dt Milliseconds to Seconds (Rotation Period)

Astrophysics, Cosmology & Relativity

Quasar

An extremely luminous Active Galactic Nucleus (AGN) powered by gas accreting onto a supermassive black hole at the center of a distant…

L_quasar ~ 10⁴⁰ W (100–1000 times Milky Way Luminosity) Luminosity / Redshift z

Astrophysics, Cosmology & Relativity

Red Giant

A large, luminous star in a late evolutionary stage that has exhausted core hydrogen fuel and expanded its outer envelope.

Radius R ~ 10–100 R_☉, T_surface ~ 3,000–4,500 K Solar Radii (R_☉) & Kelvin