Astrophysics and Cosmology Vocabulary Flashcards

Vocabulary flashcards covering stellar evolution, electromagnetic radiation from stars, cosmological measurement units, and expanding universe theories from the physics lecture transcript.

Planet

An object with sufficient mass for its own gravity to force it into a spherical shape, in which no nuclear fusion occurs, and that has cleared its orbit of other objects.

Dwarf planet

A planet-like body that has not cleared its orbit of other objects.

Planetary satellite

A body that orbits a planet.

Asteroid

An object that is too small and uneven in shape to be a planet, orbiting the Sun in a near-circular orbit.

Comet

A small, irregularly sized ball of rock, dust, and ice that orbits the Sun in an eccentric elliptical orbit.

Solar system

A system containing stars and orbiting objects such as planets.

Galaxy

A collection of stars, dust, and gas, typically containing around 100 billion stars.

Nebula

A gigantic cloud of dust and gas that serves as the birthplace of all stars.

Protostar

A sphere of very hot, dense dust and gas formed by gravitational collapse before nuclear fusion begins.

Solar mass ($M_\odot$)

A unit of mass equal to the mass of our Sun's core, defined as $1.99 \times 10^{30}\,\text{kg}$.

Red giant

An evolved stage of a low-mass star (core mass between $0.5 M_\odot$ and $10 M_\odot$) formed when core hydrogen depletes, causing the core to collapse and shell fusion to occur.

Planetary nebula

The outer layers of a red giant that drift off into space as helium nuclei run low.

White dwarf

The dense remaining core of a low-mass star with a surface temperature of around $3000\,\text{K}$, where no fusion occurs.

Electron degeneracy pressure

The pressure arising because two electrons cannot exist in the same quantum state, preventing a white dwarf core from collapsing under gravity.

Chandrasekhar limit

The maximum mass for a stable white dwarf star core, equal to $1.44 M_\odot$.

Red supergiant

An evolutionary phase of a massive star (mass in excess of $10 M_\odot$) where high core temperatures allow fusion of helium into heavier elements up to an inert iron core.

Type 2 supernova

An explosion caused by the collapse of a massive star's iron core, creating a shockwave that ejects outer shells into space and synthesizes elements heavier than iron.

Neutron star

An extremely small, dense stellar remnant formed when protons and electrons combine in a collapsing core with mass greater than $1.44 M_\odot$.

Black hole

A remnant of a massive star whose remaining core mass exceeds $3 M_\odot$, creating gravitational fields so intense that escape velocity exceeds the speed of light.

Hertzsprung-Russell (HR) diagram

A plot of stellar luminosity against absolute temperature used to determine a star's evolutionary stage and spectral class.

Emission line spectra

A spectrum consisting of a series of sharp colored lines on a black background, unique to each element due to its discrete electron energy levels.

Continuous line spectra

A spectrum containing all visible wavelengths of light, produced by atoms of solid heated metals.

Absorption line spectra

A continuous spectrum containing dark spectral lines corresponding to specific wavelengths absorbed to excite atoms of a particular element.

Diffraction grating

An optical component with regularly spaced slits that diffracts light according to $d \sin(\theta) = n\lambda$.

Wien's displacement law

The law stating that the black body radiation curve for a given temperature peaks at a wavelength inversely proportional to absolute temperature, given by $\lambda_{\text{max}} T = 2.9 \times 10^{-3}\,\text{m\,K}$.

Stefan's law

The law stating that the total radiant heat energy emitted per unit surface area of a black body is proportional to the fourth power of its absolute temperature, given by $L = 4\pi r^2 \sigma T^4$.

Astronomical Unit (AU)

The average distance from the Earth to the Sun, defined as $1.5 \times 10^{11}\,\text{m}$.

Light year (ly)

The distance travelled by light in one year, equal to $9.46 \times 10^{15}\,\text{m}$.

Parsec (pc)

The distance at which a radius of $1\,\text{AU}$ subtends an angle of $1\text{ arcsecond}$, equivalent to $3.1 \times 10^{16}\,\text{m}$.

Stellar parallax

The apparent shift in position of a nearby star against a backdrop of distant objects, used to calculate distance via $d = \frac{1}{p}$.

Cosmological principle

The principle asserting that the universe is isotropic, homogeneous, and governed by universal physical laws on a large scale.

Isotropic

The property of the universe being identical in all directions to every observer, having no distinct center or edge.

Homogeneous

The property of the universe where matter is uniformly distributed such that density is constant across large volumes.

Doppler Effect

The apparent shift in wavelength observed when a wave source moves relative to an observer or detector.

Hubble's law

The observation that the recessional velocity $v$ of a galaxy is proportional to its distance $d$ from Earth, given by $v = H_0 d$.

Hubble constant ($H_0$)

The constant of proportionality in Hubble's law, equal to $67.8\,\text{km\,s}^{-1}\text{Mpc}^{-1}$.

Big Bang theory

The cosmological model stating that space, time, and all matter in the universe originated from a dense, hot singularity that rapidly expanded.

Dark Energy

A hypothetical form of energy filling all space that drives the accelerating expansion of the universe, theorized to account for 68% of total universe energy.

Dark Matter

A hypothetical, non-luminous form of matter inferred from galactic rotation curves, theorized to make up 27% of the mass in the universe.