Â鶹ÒùÔº

By analyzing the data from ESA's Gaia satellite, astronomers from the University of Chicago, Illinois and elsewhere, have identified a new ultra-metal-poor star. The newfound star, designated GDR3_526285, turns out to be one of the most metal-poor stars detected so far. The finding was announced in a published August 8 in The Astrophysical Journal Letters.

Ultra-metal-poor (UMP) stars (with iron abundances [Fe/H] below -4) are extremely rare, given that only a few dozen of such objects have been identified to date. They are assumed to be direct descendants of the first (Population III) stars and therefore could offer important insights into the conditions in the early universe.

Now, a group of astronomers led by University of Chicago's Guilherme Limberg reports the detection of a new UMP star, GDR3_526285, in Gaia's blue photometer (BP) and red photometer (RP) spectro-photometric catalog—Gaia BP/RP (XP). The status of the star was confirmed by multi-band photometry and high-resolution spectroscopic analysis using the Magellan Clay 6.5 m telescope at Las Campanas Observatory in Chile.

"We have identified this extraordinary star among the Gaia DR3 [Data Release 3] low-resolution XP spectra, and combined multi-band photometry with high-resolution spectroscopy to derive stellar parameters and chemical abundances," the researchers wrote in the paper.

GDR3_526285 was found at a distance of approximately 78,600 light years away from the Earth, in the Milky Way's halo. It has a metallicity at a level of -4.82 dex, which is one of the lowest iron abundances ever measured. Moreover, it also has one of the lowest metal mass fractions among the known metal-poor stars.

According to the study, the mass of GDR3_526285 is assumed to be about 0.78 solar masses. The effective temperature of this star was estimated to be some 4,600 K, and its line-of-sight velocity was measured to be 428.7 km/s.

The study found that GDR3_526285 has a relatively low upper limit to the nominal carbon-to-iron ratio—at a level of 1.18. This means that it does not have a strong carbon overabundance, which is observed in other UMP stars with similar metallicities.

Based on the results, the authors of the paper suppose that GDR3_526285 likely formed from dust-cooled gas rather than fine-structure line cooling due to carbon or oxygen present in primordial gas. They assume that the star was somehow associated with satellite galaxies of the Milky Way—the Magellanic Clouds.

"The kinematics of GDR3 526285 make it tentatively linked to the Magellanic system, either by being dynamically perturbed by its recent infall or as a former LMC [Large Magellanic Cloud] star that has been tidally stripped by the Milky Way," the scientists conclude.

© 2025 Science X Network