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The stars in the faint dwarf galaxy Pictor II are home to PicII-503, an iron-deficient second-generation star. |Image source: CTIO/NOIRLab/DOE/NSF/AURA Image processing: Image processing: TA Rector (University of Alaska Anchorage/NSF NOIRLab), M. Zamani and D. de Martin (NSF NOIRLab) Acknowledgments: PI: Anirudh Chiti, Alex Drlica-Wagner
Scientists playing “cosmic archaeologists” have discovered a rare, iron-deficient second-generation star – essentially a fossil record of the chemical evolution of the universe. Just as the discovery of artifacts on Earth teaches us about lost generations of humanity, this observation provides hard evidence of how the first generation of stars died, chemically enriching their successors.
The second generation, or POP II, Star Found among dwarves galaxy Pictor II is located about 150,000 light-years away in the constellation Pictor, using dark energy camera (DECam) mounted on top of the VÃctor M. Blanco 4-meter telescope. The star, named PicII-503, has only 1/40,000 the iron content of the Sun and is a third-generation or (somewhat confusingly) POP I star. In fact, PicII-503 has the lowest iron concentration ever Milky Way Making it one of the most primitive stars ever discovered.
However, this flaw is not the most special thing about PicII-503. The team also found that the POP II star is very carbon-rich, with a carbon-to-iron ratio that is more than 1,500 times higher than that in the sun. This excess reflects the unique carbon signature of low-iron stars found in the outer halo of the Milky Way’s nebulae.
“Discoveries like this are cosmic archaeology, uncovering rare stellar fossils that preserve the fingerprints of the universe’s first stars,” said Chris Davis, director of the National Science Foundation’s NOIRLab program. said in a statement.
a kind of magic
The first stars in the universe, or POP III stars, were born before the chemical abundance of the universe was exceeded. hydrogenhelium and small amounts of heavier elements, collectively known as “metals” by astronomers. This means that these POP III stars are also dominated by hydrogen, with only a small amount of helium, and have very little metal content. These stars formed the first carbon and iron in their cores, and these materials were distributed into the interstellar medium as the stars entered it. supernova And explode at the end of life.
Clouds of interstellar gas and dust rich in these metals eventually cooled and collapsed, giving birth to a second generation of stars that were even richer in metals thanks to heavy elements supplied by their predecessors. This makes POP II something like a time capsule, recording an important stage in the chemical enrichment of the universe.
“Given the extreme rarity of these objects, finding a star that unambiguously retains the heavy metals present in the first stars is on the edge of what we think is possible,” team leader Anirudh Chiti of Stanford University said in the statement. “PicII-503’s iron abundance is the lowest ever of any ultrafaint dwarf galaxy, providing an unprecedented window into the creation of the initial elements in the primordial system.”
PicII-503 is the first confirmed example of a POP II star discovered in a faint dwarf galaxy, and was highlighted as an extremely metal-poor star in data collected by DECam’s MAGIC (Mapping Ancient Galaxies in CaHK) survey. The express purpose of this 54-night observing campaign was to identify the oldest and most chemically primitive stars in the Milky Way and its dwarf galaxy companions.
“Without the MAGIC data, it would have been impossible to separate this star from the hundreds of other stars in the vicinity of the Pictor II ultrafaint dwarf galaxy,” Chitty said.
Chiti and colleagues compared MAGIC data with data from very large telescope (VLT) in the Atacama Desert region of northern Chile and the Bad Magellan Telescope discovered PicII-503’s low iron and calcium abundances, the lowest observed outside our own galaxy. This, in turn, suggests that PicII-503 is the first record of chemical enrichment found in a dwarf galaxy.
The Dark Energy Camera is mounted in the Victor Blanco telescope, and this image was taken with other telescopes at the Inter-American Observatory in Monte Tololo, Chile. |Image source: Fermilab
One possible explanation for PicII-503’s extremely low iron-to-carbon ratio is that when POP III stars go supernova, the energies of these explosions are relatively low. This means that while lighter elements like carbon are ejected into the interstellar medium, heavier elements like iron fall back into the supernova remnants.
The fact that PicII-503 was discovered in one of the smallest dwarf galaxies ever discovered, with a correspondingly low gravitational influence, supports the idea that POP III stars die in low-energy supernovae.
“What excites me the most is that we are observing the consequences of the production of the first elements in the original galaxy. This is a fundamental observation!” Chitty said. “It also clearly links to the signatures we see in the lowest metallicity galactic halo stars, linking their origins to the first star-rich nature of these objects.”
The team’s findings were published in the journal on Monday (March 16) Natural Astronomy.
