Artist’s impression of Population III stars as they would have appeared 100 million years after the big bang
NOIRLab/NSF/AURA/J. da Silva/Spaceengine/M. Period
We may have finally seen the first generation of stars. Astronomers have been searching for these primordial giants, called population III stars, for decades. They have now found what may be the most promising candidate yet.
Population III stars are expected to be very different from modern or Population I stars. They would have formed from pristine hydrogen and helium gas, before the heavier elements were distributed throughout the universe by supernovae and powerful stellar winds. They are also expected to be larger and hotter than modern stars.
That’s exactly what Eli Visbal of the University of Toledo in Ohio and his colleagues discovered when they performed a detailed analysis of previous James Webb Space Telescope (JWST) observations of a distant galaxy called LAP1-B. It’s at a redshift – a number astronomers use to measure distance – of 6.6, which means we’re seeing LAP1-B as it was about 800 million years after the big bang. It’s so far away that the only reason we’ve been able to spot it is because its light was amplified by a closer galaxy cluster in a process called gravitational lensing.
“There should be tons and tons of them everywhere in the observable universe, but we can only look under the lamplight of this light-magnifying cluster,” Visbal says. When he and his team calculated how many Population III star clusters we should find at this redshift, they found that there should be about one – and that’s what they saw. “Our abundance estimate was in perfect agreement with [the previous research team] find one where they did,” he said.
Another point in favor of LAP1-B is that it appears to contain enough stars to be a few thousand times the mass of the sun. Other candidate galaxies for Population III tend to have much higher stellar masses, which does not match simulations of Population III star cluster formation. “He’s the best candidate we have so far,” Visbal says.
Most Population III stars are expected to have lived and died between 100 and 400 million years after the Big Bang, after which there would have been enough heavy elements in the cosmos to form stars more like those we see today. “This item ticks a lot of boxes, but I’m a little skeptical because it’s late in the game for these stars to be there, and there may be alternatives that could also do the trick,” says Ralf Klessen of the University of Heidelberg in Germany. “It would be very interesting to see a population III star cluster, but statistically it would definitely be an outlier.”
However, it is possible that pockets of pristine hydrogen and helium survive longer and later form Population III stars, Visbal says.
“LAP-B1 is an extremely interesting candidate, but it is still far from having the clear and unambiguous signatures that we expect for clean detection of Population III,” says Roberto Maiolino of the University of Cambridge. “[For these to be Population III stars]it must be an extremely fortunate combination of different factors, each extremely rare in itself, and much rarer when they must occur together. It will take deeper observations and more detailed simulations to know for sure whether LAP1-B marks the first time we have seen these strange stars.
This is important because understanding Population III stars is crucial to determining how and when the first heavy elements formed. “They can tell us how the chemistry of the universe evolved, from hydrogen and helium to all the cool chemistry and life and everything we have in the universe today,” Visbal says. Population III stars were the first building blocks of the complexity that surrounds us today.
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