When does the universe “wake up”? Ancient galaxies may reveal the process of cosmic transformation

BEIJING, Feb. 11 (Xinhua) — The “wake up” of the first stars is an important moment for our universe, but in the eyes of scientists, it is also unusually elusive. In a new study, a team of astronomers has discovered some of the oldest galaxies ever seen. According to the researchers, when the universe was only 680 million years old, these objects were fully formed.

The researchers also found evidence that these galaxies were releasing large amounts of ultraviolet radiation around them.

That release created huge bubbles in which neutral gases were excited and ionized, providing astronomers with the first direct image of an important period of transition in the universe.

Before dawn

Long ago, there were no stars in the universe that sparkled. In the early days of the universe, all matter was uniform, with an average density of about the same from one place to another. This uniform, neutral universe is very different from the early stages of its birth. In earlier times, such as the first few hundred thousand years after the Big Bang, our universe was so hot and dense that it appeared as plasma;

However, by the time the universe grew to 380,000, all the chaos was over. At that time, the material was dispersed enough to be low enough to allow electrons to bind to the nucleus to form the original hydrogen and helium atoms. This occurrence released a large amount of radiation, continued to this day, and the attention of the universe microwave background radiation.

The universe has remained in this calm, neutral state for millions of years. But as the universe expands and cools, tiny “seeds” begin to form, and some gases are slightly denser than their surroundings for some occasional reason. This tiny increase in density gives them tiny gravitational edges that attract the surrounding matter. As gas clusters grow, they have a greater gravitational effect, absorbing more material. Over the long years, the first stars and galaxies grew little by little in the silent, dark, neutral universe.

The “wake up” of the universe

We don’t know when the first stars formed, but what is certain is that they formed in a huge and wonderful way. As they formed, the universe became no longer neutral, but ionization occurred.

Most of the matter we come into contact with every day is made up of complete atoms, and all nuclei are surrounded by electron shells. Chemical reactions are like a wonderful and complex dance in which the electron shell layers of different atoms rotate and bind to each other. But in practice, this is not common in the universe. Until now, the vast majority of matter in the universe has been plasma, and as long as a long time ago, electrons and nuclei are free to exist independently. The sun is plasma, and other stars are plasma; It’s also plasma.

When the universe grew to 380,000, it went from plasma to neutral gas. Today, 13 billion years later, most of the universe is plasma. There must be some reason why most of the atoms in the universe have split. Given that we have made as much observation of the plasma universe as possible, dating back to some of the stars and galaxies that first appeared on the stage of the universe, whatever the cause of this “reionization”, this process must have happened a long time ago.

Astronomers believe that the extreme ultraviolet radiation released by the first generation of stars (and the process by which they erupted and died as supernovae) turned the universe back into plasma. But it is frustrating that we do not know exactly when this change occurred. Even the most powerful telescopes, and the deepest survey techniques, do not have the ability to look back on the universe so long ago. We can clearly see the cosmic microwave background radiation, and we can clearly see the universe today, but the middle part is still an open mystery until now.

We don’t know when the first stars appeared – astronomers call edited the event as “Dawn of the Universe” – and we don’t know when the subsequent “reionization era” began.

Plasma bubbles

That is beginning to change. Astronomers are looking for older galaxies to study the gases around them in an attempt to understand this important period of the universe’s growth and evolution. Recently, an international team of researchers discovered three galaxies that are incredibly small and incredibly far away from us.

When our universe is only 680 million years old, these small galaxies are fully formed and operational. This is not surprising, since the same ancient galaxies have been discovered before. But in the study, the researchers found a new finding: By detecting radiation from the environment around the three galaxies, they found that these galaxies had begun to blow ionizing plasma bubbles around them.

In other words, the radiation released from these galaxies has begun to change the surrounding universe. This is the first clear indication that the period of reionization continues. Although astronomers speculated that the universe had been re-ionizing in a billion years, no one thought the process would happen so early.

These galaxies are the perfect targets for the soon-to-launch (expected March 30, 2021) James Webb Space Telescope, which was designed to study this period in the history of the universe. If the results are true and more examples of reionization can be found in the future, we may eventually be able to understand this period of transition from the oldest and most dramatic history of the universe. Details of the study were published on January 7 on the preprinted paper website arXiv.org.