What the first stars were like is a mystery. When we look back into the early Universe’s dim depths, we only perceive ghosts of their existence.
But new evidence found in images from the James Webb Space Telescope seems to agree with a recent idea that is gaining traction: that fusion-powered balls of heat and fury with masses up to 10,000 Suns appeared soon after the appearance of the first stars, if not among them.
Today, owing to data obtained by the James-Webb Space Telescope, we believe we have found the first sign of the presence of these remarkable stars, says astrophysicist Corinne Charbonnel of the University of Geneva in Switzerland.
A globular cluster, a particular kind of star cluster, is the initial component in this puzzle. There are about 157 globular clusters in the Milky Way, therefore they are relatively common in our local universe. They are extremely dense, spherical clusters containing anything from 100,000 to 1 million stars, and the chemical features of those stars all but guarantee that they formed at the same time, out of the same cloud of gas.
They are also commonly made up of elderly stars on the verge of extinction, and as such are considered “fossils” of the early Universe by astronomers who study them to better understand the chemical makeup of the cosmos.
But these older globular clusters have some strange characteristics. Chemical abundance ratios, such as an enrichment of helium, nitrogen, and sodium and a relative depletion of carbon and oxygen, are seen and are challenging to explain.
Hydrogen burning at very high temperatures is the most likely explanation for these abundances. In 2013, scientists proposed that the cores of big stars could be the sites where such high temperatures could be achieved. Massive star systems. The cores of these supermassive stars are far hotter and under much higher pressures than those of the stars we see in the night sky today, and they weigh up at roughly 10,000 solar masses.
In 2018, Charbonnel and her colleague Mark Gieles, formerly of the University of Surrey but now of the University of Barcelona, in Spain, concluded that it was feasible that the interstellar medium of globular clusters had been “polluted” with these elements by the stellar wind released by these stars. Meanwhile, regular t-bone rides from nearby stars kept the star’s mass from dwindling. If stars formed from the contaminated interstellar material, they would take on the chemical abundances seeded by the early Universe’s giant stars.
Those ancient polluting stars have passed on, and their faint glow from surrounding clusters is no longer visible.
In contrast to the stellar longevity of two million years, “globular clusters are between 10 and 13 billion years old,” Gieles explains. So, in the clusters, we can see now, they vanished pretty quickly. There are no direct signs; only vestiges.
It’s all very orderly, but additional empirical proof was needed. The JWST then looked at a distant galaxy called GN-z11, which has been hiding in the cosmos for barely 440 million years since the Big Bang and whose light is only now reaching us after a 13.3 billion-year journey through an ever-expanding universe.
Although GN-z11 has been known to us for some time, it required the most powerful space observatory ever built, JWST, to analyze the light spectrum it has transmitted to us across space and time.
The incoming information turned out to be peculiar. Nitrogen is more abundant in the interstellar medium of GN-z11 than oxygen is, with an abundance ratio greater than four times that of the Sun. curios, if in line with astronomers’ observations of the development of globular clusters.
After extensive analysis and modeling, Charbonnel and her team found that the abundance ratios in globular clusters like GN-z11 can be consistently explained by giant stars with masses between about 1,000 and 10,000 solar masses that formed through runaway collisions of smaller objects.
Charbonnel explains that the simulations of Master’s student Laura Ramirez-Galeano reveal that the strong presence of nitrogen can only be explained by the combustion of hydrogen at extremely high temperatures, which can only be reached in the core of supermassive stars.
While the data does not provide a definitive answer, it does point us in the right direction. These early Chonker stars may be identified with the help of more data on early galaxies that the researchers hope to get from JWST. This, in turn, could shed light on questions like the nature of the first stars in the Universe and the formation of supermassive black holes.
The researchers note that if the supermassive star scenario can be firmed up by future studies, it would be a significant step towards understanding globular clusters and the creation of supermassive stars in general.
“Anyway, the peculiar properties of GN-z11 just revealed by JWST call for further studies to understand the physical processes ongoing in such extreme objects in the early Universe and their possible connection with the formation of globulars, supermassive stars, and potentially also supermassive black holes,” the authors write.