SDSS J0715-7334 is a newly identified ultra‑metal‑poor star located about 80,000 light years away, in the vicinity of the Large Magellanic Cloud. It contains less than 0.005% of the metals found in the sun and is composed almost entirely of hydrogen and helium. Because of its chemical simplicity, researchers describe it as the closest known analogue to the Population III stars that formed at the dawn of the universe.
The object was flagged for follow-up in 2014 by coauthor Kevin Schlaufman as part of the fifth generation of the Sloan Digital Sky Survey. A team obtained high‑resolution spectra with the Magellan Clay Telescope and its Magellan Inamori Kyocera Echelle spectrograph to measure the star’s composition. The data show only trace amounts of carbon and iron, leading the team to conclude the gas that formed the star had been recently mixed with material ejected by a Population III supernova.
By modelling the observed element ratios, astronomers can infer the mass of that original Population III star and the energy of its explosion; the composition suggests that progenitor was unusually massive and exploded with uncommon vigor. As first author Alexander Ji notes, these pristine stars act as indirect windows into the dawn of stars and galaxies. The study appears in Nature Astronomy, lists many coauthors from different institutions, and received support from several national and international funding agencies.
- The Large Magellanic Cloud is the largest of the 100–200 small satellite galaxies around the Milky Way.
- The Magellanic Clouds joined the Milky Way relatively recently and drew gas from the cosmic web for a long time.
- Those conditions may have helped produce low‑metallicity stars like SDSS J0715-7334.
Difficult words
- composition — mixture of elements and chemical parts
- spectrum — range of light from an objectspectra
- infer — form a conclusion from evidence
- progenitor — an earlier star that produced material
- pristine — very clean or unchanged since formation
- vicinity — the area near a particular place
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Discussion questions
- What can finding stars with very low metal content tell us about the early universe? Give two reasons from the article.
- The article says the gas that formed the star was mixed with material from a Population III supernova. How might that mixing affect later star formation?
- The Magellanic Clouds drew gas from the cosmic web and may have helped form low-metallicity stars. How could interactions between galaxies change conditions for star formation?
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