Early Universe’s stars had up to several hundred solar masses. The earliest stars of 140-260 solar masses became pair-instability supernovae (PISNe). These stellar explosions would have left a unique chemical signature in the atmosphere of next-generation stars that is quite unlike that of Type II and Type Ia supernovae. But there was no sign of this signature — until now. In a new study, astrophysicists show that LAMOST J1010+2358, a very metal-poor in the Galactic halo, is clear evidence of PISN from very massive first stars in the early Universe.
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; 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. Image credit: NAOC.
“Our study provides an essential clue to constraining the initial mass function of stars in the early Universe,” said Monash University’s Professor Alexander Heger.
“Before this study, there was no evidence of PISN in the first generation of stars.”
LAMOST J1010+2358 was identified as a very metal-poor star by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey.
Using the Subaru telescope, Professor Heger and colleagues conducted a follow-up high-resolution spectroscopic observation of the star.
They were able to calculate abundances for over ten elements in LAMOST J1010+2358.
They found that the star has low sodium and cobalt abundances; its sodium-to-iron ratio is below 1/100 that of the Sun.
LAMOST J1010+2358 also has a big difference in the abundance of elements with odd and even charge numbers, like sodium, magnesium, cobalt, and nickel.
“Sodium, magnesium, cobalt, and nickel abundances show a pattern unique to PISNe,” Professor Heger said.
“The peculiar odd-even variance, along with deficiencies of sodium and α-elements in this star, are consistent with the predicted chemical fingerprint of primordial PISN from first-generation stars with 260 solar masses.”
According to the astronomers, LAMOST J1010+2358 is clear evidence of PISN supernovae.
“This type of supernova is due to a hydrodynamical instability caused by electron-positron pair formation at the end of a very massive star’s life,” they said.
“PISNe disrupt the entire star, leaving no remnant. A PISN explosion can be from a few up to a hundred times more powerful than a normal supernova.”
“The explosion that made LAMOST J1010+2358 was among the most energetic PISNe.”
“The iron abundance of LAMOST J1010+2358 is substantially greater than the most metal-poor stars in the Galactic halo, suggesting that second-generation stars created in the gas dominated by PISN ashes can be quite metal-rich.”
“LAMOST J1010+2358 may be the oldest star we know,” Professor Heger said.
“The stars that make PISN have the shortest lifetimes, and the metal-rich gas they make can form the next generation of stars — those we observe — more swiftly than the metal-poorer gas that makes the stars known before. No star of the first generation has ever been found.”
“The identification of such a massive primordial star suggests that the first stars were more massive than stars forming in the present Universe.”
“This confirms why we never found long-lived low-mass primordial stars.”
“One of the holy grails of searching for metal-poor stars is to find evidence for these early pair-instability supernovae,” said Harvard University’s Professor Avi Loeb.”
“This study presents what is, to my knowledge, the first definitive association of a Galactic halo star with an abundance pattern originating from a PISN,” added Notre Dame University’s Professor Timothy Beers.
The findings appear in the journal Nature.
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QF. Xing et al. A metal-poor star with abundances from a pair-instability supernova. Nature, published online June 7, 2023; doi: 10.1038/s41586-023-06028-1
