In the Beginning: Big Bang Theory and Formation of Light Elements

Vocabulary flashcards covering key terms and concepts from the lecture on the Big Bang, nucleosynthesis, stellar evolution, atomic structure, and related cosmological evidence.

Physical Science

Branch of natural science that studies non-living systems, including chemistry, physics, astronomy, and related fields.

Cosmology

Area of astronomy that investigates the origin, evolution, structure and ultimate fate of the universe.

Big Bang Theory

Scientific model stating the universe began about 13.7–15 billion years ago from an extremely hot, dense state and has been expanding ever since.

Singularity

Initial point of the Big Bang where the universe was infinitely hot, dense, and occupied an infinitesimal volume.

Inflation

Brief epoch (≈10⁻³⁶ s) of exponential expansion immediately after the Big Bang that smoothed and stretched space.

Nucleosynthesis

Process of creating new atomic nuclei from pre-existing protons and neutrons through nuclear reactions.

Big Bang Nucleosynthesis

Formation of the light elements (H, He, Li) within the first few minutes after the Big Bang.

Stellar Nucleosynthesis

Fusion reactions inside stars that build elements from beryllium up to iron during stellar lifetimes.

Supernova Nucleosynthesis

Rapid creation of elements heavier than iron during a supernova explosion via neutron-capture (r-process).

Stellar Evolution

Life cycle of a star from formation in a nebula through stages such as main sequence, giant, and possible supernova or white dwarf.

Main Sequence Star

Stable star phase where hydrogen fusion in the core balances gravity, e.g., the Sun.

Red Giant

Later evolutionary stage of a low- to mid-mass star characterized by an expanded, cooling outer envelope.

Supernova

Catastrophic explosion of a massive star that ejects heavy elements and triggers r-process nucleosynthesis.

White Dwarf

Dense stellar remnant of a low- or medium-mass star after outer layers are shed; no further fusion occurs.

Neutron Star

Extremely dense core left after a massive star’s supernova; composed almost entirely of neutrons.

Black Hole

Region of spacetime whose gravity is so strong that nothing, not even light, can escape; end state of very massive stars.

Recombination

Epoch (~300 000 years after Big Bang) when electrons and protons combined to form neutral hydrogen, allowing photons to travel freely.

Cosmic Microwave Background (CMB)

Relic electromagnetic radiation left over from recombination; uniform 2.7 K microwave glow across the universe.

Redshift

Shift of spectral lines toward longer wavelengths indicating an object is moving away, evidence of universal expansion.

Annihilation

Reaction in which a particle and its antiparticle collide and convert their mass into energy (photons).

Pair Production

Creation of a particle–antiparticle pair from energy, essentially the reverse of annihilation.

Isotope

Atoms of the same element (same atomic number) that differ in neutron number and mass number.

Proton

Positively charged subatomic particle located in the nucleus; defines an element’s atomic number.

Neutron

Electrically neutral subatomic particle in the nucleus contributing to atomic mass.

Electron

Negatively charged subatomic particle orbiting the nucleus; equal in number to protons in a neutral atom.

Atomic Number (Z)

Number of protons in an atom’s nucleus; determines the element’s identity.

Mass Number (A)

Sum of protons and neutrons in an atom’s nucleus.

Ion

Atom or molecule with unequal numbers of protons and electrons, giving it a net charge.

Alpha Decay

Radioactive process where an unstable nucleus emits a helium-4 nucleus (α-particle) to decrease mass and atomic number.

Beta Decay

Radioactive transformation in which a neutron converts to a proton (β⁻) or a proton to a neutron (β⁺), emitting an electron/positron and neutrino.

Gamma Decay

Release of high-energy photons (γ-rays) from an excited nucleus without changing atomic number or mass number.

Proton-Proton Chain

Series of fusion reactions in stars like the Sun that convert hydrogen into helium and release energy.

Triple-Alpha Process

Fusion reaction inside red giants where three helium-4 nuclei combine to form carbon-12.

Neutron Capture

Process in which a nucleus absorbs a neutron, leading to heavier isotopes or new elements.

s-Process

Slow neutron-capture pathway in relatively low neutron flux where beta decay occurs between captures; builds elements up to bismuth.

r-Process

Rapid neutron-capture pathway in high neutron flux (e.g., supernovae) that forms very heavy, neutron-rich nuclei.

Relative Abundance

Proportion of a given isotope or element compared to others in a sample or the universe.

Visible Spectrum

Portion of the electromagnetic spectrum visible to the human eye, ranging roughly 400–700 nm.

Periodic Table of Elements

Tabular arrangement of chemical elements ordered by atomic number, electron configuration, and recurring properties.

Atomic Mass Unit (amu)

Mass scale (1 amu ≈ 1/12 of a carbon-12 atom) used to express atomic and molecular masses.

Pair Annihilation

Specific annihilation event where an electron and positron destroy each other, producing photons.

Seed Nucleus

Existing nucleus that captures neutrons during s- or r-process nucleosynthesis.

Relative Abundance of H & He

Observed cosmic ratios (~75 % H, 25 % He by mass) that support Big Bang nucleosynthesis predictions.