Explosive Stellar Phenomena and Advanced Nuclear Astrophysics

Vocabulary and key concepts from the first lecture on Advanced Nuclear Astrophysics, covering the nuclear landscape, stellar fusion processes, and observational evidence for nucleosynthesis.

Nuclear Composition of Matter

Nuclei comprise $99.9\%$ of the matter observed in the Universe and serve as the fuel for stars.

Isotope Discovery Rate

The rate at which new isotopes are discovered is approximately $30 / \text{year}$, according to Thoenessen (2014).

Drip Line

The boundary on the nuclear landscape beyond which nuclei become unbound; the transcript specifically identifies the two-proton and two-neutron drip lines.

Triple Alpha Process

A stellar fusion reaction where three helium nuclei combine to form carbon: $^4\text{He} + ^4\text{He} + ^4\text{He} \rightarrow {}^{12}\text{C} + X + \text{energy}$.

Carbon Fusion

A nuclear reaction in stars where two carbon nuclei fuse to create magnesium: ${}^{12}\text{C} + {}^{12}\text{C} \rightarrow {}^{24}\text{Mg} + X + \text{energy}$.

Iron Peak (${}^{56}\text{Fe}$)

The point on the binding energy curve where average binding energy per nucleon is highest; fusion is exothermic for nuclei lighter than this, while fission is exothermic for heavier nuclei.

Big Bang Nucleosynthesis (BBN)

A process in the early universe that only produced elements up to Carbon ($Z=6$); elements with an atomic number Z > 6 were produced later in astrophysical sources.

Abundance Normalization

In abundance plots of the elements, the abundance of Silicon (Si) is typically normalized to $10^6$.

Coulomb Barrier

The electrostatic force that makes it difficult for charged particle reactions to occur in stars above a mass number of $A \sim 60$.

Technetium (Tc) Observation

Direct evidence of stellar nucleosynthesis provided by Merrill (1952), who observed radioactive Technetium (\tau_{1/2} > 4\,\text{Myr}) in stellar spectra.

Aluminum-26 (${}^{26}\text{Al}$)

A radioactive isotope ($\tau_{1/2} \sim 7.2 \times 10^5\,\text{yr}$) whose detection via $\gamma$-rays at $1.8\,\text{MeV}$ in satellite observations provides evidence of active nuclear physics in stars.

Supernova 1987A (SN 1987A)

An astrophysical event that provided direct evidence of nucleosynthesis through the detection of neutrinos.

Cobalt-56 (${}^{56}\text{Co}$) Decay

The radioactive decay ($\tau_{1/2} \sim 77\,\text{days}$) that powers the light curves of core-collapse supernovae as it decays into ${}^{56}\text{Fe}$.

Cassiopeia A

A $320\text{-year-old}$ supernova remnant where X-ray and $\gamma$-ray astronomy has detected elements such as Magnesium and Sulfur, as well as the decay of ${}^{56}\text{Co}$ and ${}^{57}\text{Co}$.

Galactic Winds

Large-scale outflows of gas from galaxies that are driven by energy from supernova explosions.