What wavelength arrives?
Radio to gamma ray.
Different wavelengths reveal different physical processes and temperatures.
Side 49
Astronomy &
Cosmology
A study of the universe across scale and time. Astronomy observes objects and processes; cosmology asks how the universe as a whole evolved from an early hot dense state into the large-scale structure observed today.
light→object→gravity→structure→cosmic history
06cosmic scales
05observational tools
05cosmology questions
49Side
Astronomy learns from signals that have already traveled.
Most cosmic knowledge arrives through electromagnetic radiation, supplemented by particles and gravitational waves.
Which frequencies are present?
Lines + continuum.
Spectra reveal composition, temperature, velocity and physical conditions.
How is wavelength displaced?
Motion or cosmic expansion?
Redshift carries information about relative motion and, on cosmological scales, expansion.
How far away is the source?
Parallax, standard candle, relation?
Distance measurement uses overlapping methods across increasing scales.
How old is the observed light?
Distance is also time.
Farther observations show the universe at earlier stages of cosmic history.
Stars are gravity-powered fusion systems.
Mass largely determines stellar temperature, luminosity, lifetime and eventual fate.
Cold clouds collapse.
Gravity concentrates gas until pressure and temperature support sustained fusion.
Hydrogen fusion stabilizes the star.
Pressure generated by hot plasma balances inward gravity over most of stellar life.
The controlling parameter.
High-mass stars burn fuel much faster despite having more of it.
Stars build heavier elements.
Fusion and stellar explosions create many elements later incorporated into planets and life.
Compact remnant of lower-mass evolution.
Electron degeneracy pressure supports the remnant after nuclear fusion ends.
Explosive stellar death.
Some massive stars undergo core collapse, dispersing material and leaving compact remnants.
Galaxies are evolving gravitational systems.
Stars, gas, dust and dark matter interact across structures ranging from dwarf galaxies to giant clusters.
Disk + arms + central component.
Gas-rich disks often host ongoing star formation.
Pressure-supported stellar systems.
Many contain older stellar populations and relatively little cold gas.
Galaxies interact and combine.
Gravitational encounters can reshape morphology and trigger new star formation.
Central compact objects can power active galaxies.
Accretion onto supermassive black holes can produce enormous luminosity.
Galaxies occupy larger gravitational structures.
Clusters contain galaxies, hot gas and substantial dark matter.
Large-scale matter is filamentary.
Galaxies trace a web of filaments, sheets, clusters and voids shaped by gravitational growth.
Gravity organizes cosmic structure across enormous scales.
Under extreme density, gravity produces objects and signals far outside everyday intuition.
Orbit
Free fall around mass.
Orbital motion follows gravitational dynamics rather than requiring continuous propulsion.
Neutron star
Collapsed stellar core.
Extreme density produces matter supported by quantum and nuclear effects.
Black hole
Region bounded by an event horizon.
Within the horizon, causal structure prevents signals from escaping to distant observers.
Accretion
Falling matter converts gravitational energy.
Hot accretion disks can radiate intensely before material crosses the horizon.
Gravitational wave
Ripples in spacetime.
Accelerating asymmetric mass distributions can emit waves detectable across cosmic distances.
Cosmology studies the universe as a dynamical whole.
The standard cosmological picture combines general relativity with observations of expansion, background radiation and large-scale structure.
Early hot universe
The observable universe evolved from a much hotter, denser state.
Expansion
On large scales, distances between unbound galaxies grow as spacetime expands.
Cosmic microwave background
Relic radiation preserves information from when the universe became transparent to light.
Structure growth
Small early density differences grew under gravity into galaxies and the cosmic web.
Dark matter
An unseen gravitating component helps explain galaxy and large-scale structure dynamics.
Dark energy
Observations indicate late-time cosmic expansion is accelerating; the underlying physics remains unresolved.
Cosmology is precise and incomplete at the same time.
Measurements tightly constrain many parameters while leaving fundamental physical questions open.
What is dark matter?
Its gravitational effects are strongly inferred, but the underlying particle or physical description has not been established.
What is dark energy?
Accelerated expansion can be represented by a cosmological constant or other models, but its fundamental nature remains unknown.
What happened at the earliest accessible times?
Current theories extrapolate toward regimes where quantum gravity becomes important and established descriptions are incomplete.
Why is there more matter than antimatter?
Known physics does not yet fully explain the observed cosmic matter asymmetry.
An Introduction to Modern AstrophysicsCarroll & Ostlie · broad astrophysics
Introduction to CosmologyBarbara Ryden · cosmology foundation
CosmologySteven Weinberg · advanced framework
Black Holes and Time WarpsKip Thorne · relativity and compact objects