Written by Jonathan O'Callaghan
Machine Heart compilation
Editors: Wang Kai, Zenan
Population III stars are theorized to bring light and hope to the universe. They may have been vaguely observed by The James Webb Space Telescope (JWST).
The largest stars in the universe today are hundreds of times larger than our Sun. The earliest stars in the universe were probably 100,000 times the mass of the Sun.
A group of astronomers is poring over data observed by the James Webb Space Telescope, which vaguely captures the light emitted by ionized helium in the distant Milky Way, which may indicate that the first generation of stars existing in the universe has been discovered.
These long-searched, arbitrarily named "Population III stars" may be giant hydrogen-helium balls formed from the primordial gas of the universe. Theorists began to envision these first fireballs in the 70s of the 20th century. It is assumed that they will explode into supernovae after a short life cycle, forming heavier elements and spraying them into the universe. This stellar material later formed Population II stars, which are more abundant in heavy elements, and then even more abundant Population I stars, such as our sun, as well as planets, asteroids, comets, and eventually life itself.
"Because of our human existence, we know there must be a first generation of stars," says Rebecca Bowler, an astronomer at the University of Manchester in the United Kingdom.
Now, Wang Xin, an astronomer at the Chinese Academy of Sciences in Beijing, and his colleagues believe they have found the stars, though that idea still needs to be confirmed. "It's really dreamy," Wang Xin mentioned. The team's paper, which was published Dec. 8 on the preprint website arXiv, is awaiting peer review in Nature.
Even if the researchers are wrong this time, more convincing detections of the first stars may not be far off. JWST is dramatically transforming astronomical exploration and is thought to be able to see these stars far enough away in space and over a long period of time. In addition, distant galaxies have long been visible with giant floating telescopes, whose unusual brightness suggests they may contain three-star group stars. Other scientific groups now using JWST to observe stars are scrambling to analyze their own data. "It's definitely one of the hottest questions," says Mike Norman, a physicist at the University of California, San Diego, who is studying stars through computer simulations.
An authoritative and reliable discovery will allow astronomers to begin exploring the size and appearance of stars, how long they exist, and how they suddenly light up in the primordial dark universe.
"This is really one of the most fundamental changes in the history of the universe," Bowler said.
Population III
German astronomer Walter Baade divided the stars in our galaxy into Type I and Type II in 1944. The latter contain older stars made up of lighter elements. Decades later, the idea of three-star stars was also documented. British astrophysicist Bernard Carr described the important role this primordial star might have played in the early universe in a paper published in 1984 that boosted their popularity. "Their heat or explosion could reionize the universe," Carr and his colleagues wrote, "... The resulting heavy elements may have accelerated the enrichment of elements in the pre-Milky Way," thus forming later more heavily enriched stars.
Carr and his co-authors speculate that stars that may have formed stars that may have been so vast that hundreds or even 100,000 times larger than the Sun should be measured everywhere due to the abundance of hydrogen and helium in the early universe.
Wang Xin, an astronomer at the Chinese Academy of Sciences in Beijing, detected helium II in the early universe, which may indicate the existence of three-star groups stars in the universe.
Those in the heavier category, the so-called supermassive stars, have relatively low surface temperatures, appear red and expanded, and are almost the size of our entire solar system. The denser, more modest three-star group variant emits hot blue light with a surface temperature of about 50,000 degrees Celsius, compared to 5,500 degrees Celsius on our sun's surface.
In 2001, Norman used computer simulations to explain how such a large star formed. In the current universe, gas clouds split into many small stars. But simulations show that gas clouds in the early universe were much hotter than modern ones, couldn't condense as easily as they do today, and were therefore less efficient at star formation. Instead, the entire gas cloud collapses to form a single giant star.
The massive mass of these stars means that their life cycles are short, lasting only a few million years at most (more massive stars can always burn out the available fuel faster). As a result, three-star group stars won't last long in cosmic history — perhaps only for a few hundred million years, until the last primordial gas dissipates.
In fact, there are still many problems, and there is a lot of uncertainty. How massive are these stars? What is the latest time they exist in the universe? How abundant were they in the early universe? Bowler said: "It's so interesting that they're completely different from the stars in our galaxy. ”
Rebecca Bowler, an astronomer at the University of Manchester in the United Kingdom, has studied the formation and evolution of the Milky Way in the early universe. Image by Anthony Holloway / University of Manchester
Because they are too far apart and exist for too short a time, finding evidence related to them has been a challenge. However, in 1999, astronomers at the University of Colorado Boulder predicted that the star should produce a signal that would give away signs of existence: that the light emitted by helium II or helium atoms lacking electrons would have a specific frequency as the remaining electrons of each atom transitioned between energy levels. James Trussler, an astronomer at the University of Manchester, explains that the light emitted by helium does not actually come from the star itself, but rather is produced when high-energy photons from the star's hot surface rush into the gas around the star.
Daniel Schaerer of the University of Geneva expanded on this idea in 2002 when he said, "It was a relatively simple prediction," and the search for this evidence officially began.
Search for the first generation of stars
In 2015, Schaerer and his colleagues thought they might be looking for something. They found a possible clue to a helium-II signal in a distant primordial galaxy that may be related to a group of third-star group stars. Judging by what it looked like 800 million years after the Big Bang, this galaxy seems to contain the first evidence of the first generation of stars in the universe.
Bowler-led research later questioned these findings. "We found evidence of aerobic elements at the source," she said. This precludes the possibility of pure three-star group predictions." Subsequently, an independent team failed to detect the helium-II clues found by the earliest team. "It's not there," Bowler said.
Will others be better off in the quest?
Astronomers are pinning their hopes on the December 2021 loading James Webb Space Telescope (JWST). With its massive mirror body and unprecedented sensitivity to infrared light, the telescope could observe the early universe more easily than any telescope before it. Because light travels over time, telescopes can still see faint objects that are far away despite their appearance a long time ago. In addition, the telescope can perform spectral analysis to break down light into its constituent wavelengths, which allows it to look for helium-II signatures in three-star group stars.
Wang's team analyzed spectral data from more than 2,000 JWST observation targets. One of them is a distant galaxy that appeared only 620 million years after the Big Bang. According to the researchers, the galaxy was split into two parts. Their analysis showed that half of the galaxies appeared to contain the key signal of helium II, mixed with light emitted by other elements, which could mean they are a hybrid population of thousands of third-star group stars and other stars. In addition, the spectral analysis of the other half of the galaxy has not yet been completed, but its brightness suggests that this is a more three-star environment.
"We are working to apply to cover the entire galaxy using the observation time of the next period of JWST to have an opportunity to confirm these objects," Wang said.
According to Norman, the galaxy is a "headache place." If the helium II results hold up to scrutiny, he says, "then one possibility is that this galaxy is a three-star group." However, he wasn't sure if third and later stars could mix together so easily.
Rogier Windhorst of Arizona State University is using gravitational lensing to try to zoom in on images of three-star group stars in the early universe.
Daniel Whalen, an astrophysis at the University of Portsmouth in the United Kingdom, is equally cautious. He said: "This may indeed be evidence that a galaxy has a mixture of third and second population stars. Although this may be 'the first direct evidence' of the first generation of stars in the universe, it is not conclusive evidence." Other hot cosmic objects can produce similar helium-II signals, including scorching accretion disks of hot material swirling around black holes.
Wang believes that his team can rule out the possibility that black holes are the source of this helium-II signal, because they did not detect specific oxygen, nitrogen, or ionized carbon signals, which are such possible expected conditions. However, this work remains to be peer-reviewed, and even then, follow-up observations need to confirm its potential findings.