During the James Webb Telescope’s launch in 2021, astronomers repeatedly noted its resolution and sensitivity. They made it possible to see the light of the first galaxies in the Universe, which formed several hundred million years after the Big Bang. To do this, James Webb’s mirror was directed at the most distant objects, that is, objects whose light emitted more than 12 billion years ago is only now reaching Earth. In other words, the telescope made it possible to look into the past of the universe. This is its decisive difference from previous devices.
Cosmological model under threat
Astronomers couldn’t believe their eyes when they received these images. The first galaxies of the young Universe appeared very old, that is, very large, and they managed to collect many stars over billions of years.
This conclusion was reached based on their total luminosity, which is usually related to the mass of the stars they contain. In any case, scientists had no other tool for evaluation: The telescope’s resolution was not enough to distinguish fine details, and so the galaxies appear as a bright spot. According to these data, the mass of the galaxies was approximately 50 times greater than models predicted, approaching the mass of the Milky Way, which took more than ten billion years to form.
Since mass estimates from the luminosity are considered unreliable, the current cosmological model is compromised.
He proposes that after the Big Bang, matter dispersed in gaseous form in all directions. At some point in the first 500 million years, gravity pulled together denser regions in the cooling cosmic gas to form stars and black holes. Then these stars attracted each other and gradually turned into galaxies. Over billions of years they merged with each other and grew in size.
Scientists have offered different explanations for the observed phenomenon. Some believed that the first stars, devoid of heavy elements, sparkled exotically, so that the evolution models of modern stars did not apply to them. Others have called for a complete overhaul of cosmological models. But the mystery of extreme mass probably has a conservative answer that doesn’t require scientific revolutions.
Abnormal brightness of galaxies
Chinese-born scientist Guochao Sun of Northwestern University in the United States and colleagues simulated Formation and evolution of the first galaxies. The FIRE-2 simulator used reproduced the behavior of interstellar gas and the influence of stars forming from it on it. He also took into account the consequences of supernova explosions. (a phenomenon in which a star sharply increases its brightness)), including the ejection of matter into the intergalactic medium.
As a result, it was found that the observed brightness could be explained by the high total mass. Scientists have concluded that star formation in such galaxies may occur through “bursts” (or flares) in which low star formation rates alternate. Thus, many new stars are born at the same time, which explains the temporary abnormal brightness.
“Most of the light in the galaxy comes from the largest stars. Because larger stars burn faster, they have shorter lifetimes. They consume fuel rapidly in nuclear reactions. Therefore, the brightness of a galaxy is likely to be related to how many stars it has formed over the last few million years, rather than the mass of the galaxy as a whole.” .” – explained Canadian-born scientist Claude-André Faucher-Giguere, one of the authors of the study.
The explosion of star formation in early galaxies occurs according to the following scheme. When certain conditions are reached, many stars form from the gas, and these stars explode as supernovae after a few million years. These explosions throw gas from the galaxy, and as a result of its interaction with the gases of other galaxies, new stars are formed with a simultaneous explosion millions of years later.
The cycle starts over and continues until the galaxy becomes too large for supernovae to eject gas from the galaxy. Then the flares cease and star formation in the Milky Way proceeds at approximately the same rate as in our era. Therefore, the peak brightness of the galaxies decreases and the brightness becomes almost constant.
The simulation allowed scientists to precisely capture the brightness of ancient galaxies observed in James Webb images. The numbers of observed and simulated galaxies at their peak luminosity also coincided.
James Webb’s predecessor
The idea of “flare” star formation has been floated before, but now scientists have proven the feasibility of this theory. The proposed model makes it possible to explain the paradox of very old galaxies at first glance, without making any significant changes to astrophysical models.
The launch of the Hubble telescope in 1990 was already leading to a revision of the cosmological model. Since the first half of the 20th century, astronomers have known that the Universe is expanding, but Hubble data revealed that it is accelerating. Modern physics has no clear explanation for this phenomenon, but to describe the Universe mathematically, astronomers introduced the concept of dark energy, a substance of unknown nature that produces gravitational repulsion.
Scientists are still trying to unravel the nature of dark energy, and they are unlikely to succeed in the foreseeable future.
James Webb is believed to be the same step forward that Hubble took in his time. Therefore, if some of their observations cannot be explained, astronomers will have to change the cosmological model.