In astronomy, aspects aside from hydrogen and helium are called metals. While that might make your high-school chemistry instructor cringe, it makes sense for astronomers. The 2 lightest aspects were the very first to appear in deep space. They are the atomic remnants of the big bang and comprise more than 99% of atoms in the universe. All the other elements, from carbon to iron to gold, were created through astrophysical procedures. Things like nuclear blend in stellar cores, supernova explosions, and crashes of white dwarfs and neutron stars.
Because these types of astrophysical events have actually taken place throughout the history of the universe, and continue to occur, the fraction of metals in deep space has actually increased with time. Due to the fact that of this, among the methods we categorize stars is by the amount of metals we see in their spectra. Its understood as the metallicity of a star. With metallicity, astronomers classify stars into 3 broad populations.
Population I stars, like our Sun, have the greatest amount of metals. There were plenty of large Population II stars in the past, but they have actually long since passed away, leaving white dwarfs and neutron stars. The remnant clouds of these dead stars offered the raw materials out of which Population I stars formed.
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Both of these kinds of stars have been observed in the Milky Way and other galaxies. But there is a 3rd population weve never ever seen. Population III stars would be truly ancient. They would have been the first stars to appear in deep space, with almost no metals in them. Without heavier elements to increase their density, Population III stars need to have been beasts. Brilliant blue hydrogen-helium stars hundreds of times more huge than our Sun. They would have had really brief however really bright lives. The great-grandmother stars that cast the first metals into space with their violent, explosive death. They were all gone long before our Sun formed.
However thanks to the limited speed of light, the deeper we check out the universes the further into the past we can see. So astronomers have studied some of the most distant galaxies browsing for proof of these very first stars. Now that the James Webb Space Telescope (JWST) is online, they are getting a remarkable view of extremely distant galaxies. And according to a recent research study, one group might have discovered the first glimpse of Population III stars.
Thats still after the very first stars likely formed, so much of the galaxy is most likely made up of Population II stars. Population III stars may still have been forming in the halo of gas surrounding the galaxy.
The spectral lines from this halo region show a strong HeII? 1640 line, which is the type of line emitted by helium when its exceptionally hot. Generally such a hot interstellar gas will have intense lines from “metal” aspects, however this area doesnt have that. So the HeII region seems a mix of hydrogen and helium gas that has been highly ionized by … something.
Observed halo spectra vs the AGN ionization design. Credit: Maiolino, et al
. One possibility is that the halo area might be warmed by an active stellar nuclei (AGN) at the center of GN-z11, however the approximated temperature of the halo gas and its distance from the galaxy does not really fit the AGN design. The other option is that the area was ionized by huge Population III stars. Based on the level of ionization, these stars would have been about 500 times more massive than the Sun, which remains in the hypothetical mass range of PopIII stars.
This study isnt adequate to show the presence of Population III stars, but its an engaging argument. We require more observations of these remote galaxies. And thanks to the JWST, were beginning to get them.
Reference: Maiolino, Roberto, et al. “JWST-JADES. Possible Population III signatures at z= 10.6 in the halo of GN-z11.” arXiv preprint arXiv:2306.00953 (2023 ).
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There were plenty of large Population II stars in the past, but they have actually long given that passed away, leaving white dwarfs and neutron stars. The remnant clouds of these dead stars offered the raw products out of which Population I stars formed.
Without much heavier elements to increase their density, Population III stars should have been beasts. Thats still after the very first stars likely formed, so much of the galaxy is likely comprised of Population II stars. Based on the level of ionization, these stars would have been about 500 times more huge than the Sun, which is in the hypothetical mass range of PopIII stars.
