Population III star

A hypothesized first generation of stars, formed from nearly pristine hydrogen and helium in the early universe. Their lack of heavier elements shaped their structure, lifetimes, and deaths.

Primordial gas: Gas in the early universe composed almost entirely of hydrogen and helium, with trace amounts of light isotopes. This nearly pristine material collapsed to form the first stars.
Initial mass function: The distribution of stellar birth masses in a population of stars. Its form for metal-free stars determines whether they were mostly massive or included smaller survivors.
Cosmic reionization: The epoch when ultraviolet sources ionized most neutral hydrogen in the intergalactic medium. First stars may have supplied a substantial share of the ionizing photons.
HE 1327-2326: An extremely iron-poor star in the Milky Way halo, discovered in 2005. Its unusual elemental abundances have been used to constrain the supernovae of earlier stars.
Molecular hydrogen: A molecule of two hydrogen atoms that radiates energy and enables gas to cool below atomic cooling temperatures. It was the principal coolant allowing primordial gas clouds to fragment and collapse.
Protostellar feedback: The effects of radiation, winds, and outflows from a growing protostar on its surrounding gas. Feedback may have stopped accretion and limited the masses of first-star progenitors.
Cosmic dawn: The period when the first stars and galaxies formed after the cosmic dark ages. Population III stars are among the central sources defining this transition.
SMSS J031300.36−670839.3: An ancient, extremely iron-poor star discovered in the Milky Way halo in 2014. Its carbon-rich composition offers a chemical clue to the first supernovae.
Metallicity: The abundance of elements heavier than helium in an astronomical object. Near-zero metallicity reduced cooling by heavy elements and dust during star formation.
Direct collapse black hole: A massive black hole formed when a large gas cloud collapses without first fragmenting into ordinary stars. This competing route can explain early massive black-hole seeds without requiring a stellar remnant.

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