Evidence has been found for the first stars ever to exist in the universe. The James Webb Space Telescope made these observations. This evidence comes from one of the most distant galaxies we know about.
The galaxy is called GN-z11. The Hubble Space Telescope found it in 2015. Before the James Webb Space Telescope launched, GN-z11 was considered the farthest galaxy known. It has a redshift of 10.6. This means it makes more sense to talk about when it existed, rather than how far away it is. That’s because we see GN-z11 as it was just 430 million years after the Big Bang, due to how long its light took to reach us. For comparison, the universe today is 13.8 billion years old.
GN-z11 was a main focus for the JWST to study. Two new papers describe important discoveries about GN-z11. These discoveries give us important details about how galaxies in the early universe grew.
GN-z11 is the brightest galaxy known at this redshift. In fact, it’s common for high-redshift galaxies like GN-z11 to be discovered in the early universe by the JWST. Many of these galaxies seem much brighter than our models of galaxy formation predict. These predictions are based on the standard model of cosmology.
Now, the JWST’s new observations seem to have helped us understand what’s happening.
A team of astronomers, led by Roberto Maiolino from the University of Cambridge, studied GN-z11 using two instruments on the JWST: the Near-Infrared Camera (NIRCam) and the Near-Infrared Spectrometer (NIRSpec). They found evidence for the first generation of stars, known as Population III stars, and for a supermassive black hole that is consuming large amounts of matter and growing very quickly.
Scientists can figure out the age of a star by looking at how many heavy elements it has. These elements are made by previous generations of stars that have lived and died, releasing these heavy elements into space. The elements then get reused in star-forming areas to make new stars. The youngest stars, formed in the last five or six billion years, are called Population I stars and have the most heavy elements. Our sun is one of these stars. Older stars have fewer heavy elements because there were fewer generations of stars before them. These are called Population II stars and are found in the oldest parts of our Milky Way galaxy.
Population III stars, however, have only been theoretical until now.
These would have been the very first stars to form. Because no other stars existed before them, they would have had no heavy elements and would be made only of hydrogen and helium from the Big Bang. These first stars were probably extremely bright and had masses equal to at least several hundred suns.
Although astronomers haven’t directly seen Population III stars yet, Maiolino’s team found indirect evidence of them in GN-z11. They spotted a clump of ionized helium near the edge of GN-z11 using NIRSpec.
Maiolino explained, “Since we only see helium and nothing else, it suggests that this clump must be quite pure.” Theory and simulations predict that around particularly massive galaxies from these times, there should be pockets of pure gas surviving in the halo, which could collapse to form Population III stars.
This helium gas is being ionized by something emitting a lot of ultraviolet light, which is inferred to be the Population III stars. The helium might be leftover material from the formation of those stars. It would take about 600,000 solar masses of stars in total, shining with a combined brightness 20 trillion times that of our sun, to produce enough ultraviolet light to ionize all that gas. These numbers suggest that distant galaxies like GN-z11 were better at forming massive stars than galaxies in the modern universe.
In addition, Maiolino’s team also found evidence of a two-million-solar-mass black hole at the center of GN-z11.
“We found very dense gas that is common near supermassive black holes swallowing gas,” said Maiolino. “These were the first clear signs that GN-z11 has a black hole that is eating matter.”
The team also spotted a strong burst of radiation coming from the disk of matter swirling around the black hole, as well as ionized chemical elements usually found near black holes that are swallowing matter. They say it’s the farthest supermassive black hole ever found. Its voracious appetite makes its disk of matter dense, hot, and very bright. This, along with the Population III stars, is what makes GN-z11 shine so brightly, the researchers think, without going against standard cosmology as some have claimed too early.
The study about the ionized helium clump and Population III stars will be published in the journal Astronomy & Astrophysics. Meanwhile, the study on NIRCam observations of the black hole was published on January 17 in the journal Nature.
