A metal-poor star with abundances from a pair-instability supernova

Abstract

The most massive and shortest-lived stars dominate the chemical evolution of the pre-galactic era. On the basis of numerical simulations, it has long been speculated that the mass of such first-generation stars was up to several hundred solar masses^1-4. The very massive first-generation stars with a mass range from 140 to 260 solar masses are predicted to enrich the early interstellar medium through pair-instability supernovae (PISNe)⁵. Decades of observational efforts, however, have not been able to uniquely identify the imprints of such very massive stars on the most metal-poor stars in the Milky Way^6,7. Here we report the chemical composition of a very metal-poor (VMP) star with extremely low sodium and cobalt abundances. The sodium with respect to iron in this star is more than two orders of magnitude lower than that of the Sun. This star exhibits very large abundance variance between the odd- and even-charge-number elements, such as sodium/magnesium and cobalt/nickel. Such peculiar odd-even effect, along with deficiencies of sodium and α elements, are consistent with the prediction of primordial pair-instability supernova (PISN) from stars more massive than 140 solar masses. This provides a clear chemical signature indicating the existence of very massive stars in the early universe.

Fig. 1. The abundances of J1010+2358 in comparison with those of other metal-poor stars.

J1010+2358 is shown as the red circles. The black circles indicate the metal-poor stars from the literature^,. The arrows indicate the upper limits. The error bars are 1σ uncertainties of the observed abundances.

Fig. 2. Abundance pattern of J1010+2358.

The red circles denote J1010+2358. The open symbols indicate four previously known metal-poor stars with sub-solar [Mg/Fe] ratios. The abundances of these α-poor metal-poor stars (−2.46 ≤ [Fe/H] ≤ −1.91) have been well studied on the basis of high-resolution spectroscopic analysis^,. The shaded regions indicate abundances of other metal-poor stars from the literature^,. The arrows represent the upper limits.

Fig. 3. Comparison of observed abundances and models.

The chemical abundances of J1010+2358 compared with the predictions from three theoretical supernova models^,: a 10-M_⊙ CCSN (a); a 85-M_⊙ CCSN (b); a 260-M_⊙ PISN with a 130-M_⊙ He core (c). The error bars are 1σ uncertainties of the observed abundances.

Extended Data Fig. 1. Observed spectrum of J1010+2358.

The observed spectrum of J1010+2358 (filled circles: T_eff = 5,860 K; log g = 3.6; [Fe/H] = −2.42) are shown with a comparison star J0626+6032 (blue lines: T_eff = 5,863 K; log g = 3.73; [Fe/H] = −2.39). The chemical abundances ([Na/Fe] = +0.89 ± 0.08; [Mg/Fe] = +0.21 ± 0.06; [Ba/Fe] = +0.23 ± 0.06) of J0626+6032 are normal as a VMP star. The black lines are synthetic spectra with [Na/Fe] = −2.02 ± 0.3 (a), [Mg/Fe] = −0.66 ± 0.3 (b) and [Ba/Fe] = −1.37 ± 0.3 (c).

Extended Data Fig. 2. Comparison of observed abundance pattern and SN yield models.

The chemical abundances of J1010+2358 (red circles) compared with models of combinations of SN Ia (ref. ) and CCSN (refs. ^,) with mass of 25 M_⊙: 10% contribution from SN Ia (blue line); 30% contribution from SN Ia (green line); 50% contribution from SN Ia (purple line); 70% contribution from SN Ia (orange line). The error bars are 1σ uncertainties of the observed abundances.