Scientists discover the secrets of Cosmic Reionization through simulations.

It is a part of human nature to question how everything around us came into being. That’s the reason why scientists have always been pretty keen to discover the events related to the birth of our universe. The theory of Big Bang is the most popular one in this regard which suggested that the universe came into existence following a massive explosion. Having said that, the cosmos didn’t emerge immediately after the Big Bang as darkness ruled for almost 100 million years.

The very first stars of the cosmos eventually lit up after all those years. They were the biggest and the brightest among all the stars. The intensity of their ultraviolet light was so much that it ionized the surrounding atoms. This initiated the Cosmic Dawn during which the entire process of Cosmic Reionization took place over a period of one billion years. The researching team of Michael Norman, the Director of the San Diego Supercomputer Center, wanted some in-depth analysis of this procedure and this urged them to reveal the story behind the oldest stars and galaxies. Talking about the motivation behind their study, Norman said,

“Where did these stars come from? And how did they become the galaxies—the Universe teeming with radiation and plasma—that we see today? These are our driving questions.”

They developed a computer software for their research and improved it for 20 years to better understand the Cosmic Dawn. At the very beginning, the first stars in the universe were modeled. They explained the movement and chemical reactions inside gas clouds in the dark universe. Similarly, they found the extraordinary gravitational pull of an invisible mass of mysterious dark energy. These clouds collapsed under this gravity to produce massive stars. Norman described that in the following words:

“These clouds of pure hydrogen and helium collapsed under gravity to ignite single, massive stars—hundreds of times heavier than our Sun.”

The study told the world that Lithium and Beryllium were the first heavy metals to be created in our universe. However, these short-lived giants exploded into dazzling supernovae to produce heavier metals, like Iron, in abundance. Norman mentioned that these equations were added to the Virtual Universe and it leads to the formation of a new type of star. He referred to that by saying,

“The transition was rapid: within 30 million years, virtually all new stars were metal-enriched. Formation of metal-free giant stars did not stop entirely—small galaxies of these stars should exist where there is enough dark matter to cool pristine clouds of hydrogen and helium. But without this huge gravitational pull, the intense radiation from existing stars heats gas clouds and tears apart their molecules. So in most cases, the metal-free gas collapses entirely to form a single, supermassive black hole.”

The chemical reactions with metals resulted in a new generation of stars which were smaller in size than the older ones. However, they easily outnumbered their predecessors. The process called ‘Metal Line Cooling’ was responsible for this multiplication of stars as it allows the combining elements to radiate their energy into space instead of each other. That was the point when we had galaxies in our universe for the first time because a mixture of metal-enriched stars, metal-enriched gas, and dark matter was present. Norman elaborated that these young galaxies were difficult-to-detect because the young, massive stars drove the dense gas away from star-forming regions through their intense radiation. Having said that, these galaxies made some substantial contributions to the Cosmic Reionization.

The researching team also mentioned that some groups have succeeded in overcoming computing limitations in these mathematical simulations by importing their ready-made results. Likewise, the researchers referred to some areas of uncertainty that will drive a new series of simulations. The study said,

“These semi-analytical methods have been used to more accurately determine how long massive metal-free early stars were being created, how many should still be observable, and the contribution of these—as well as black holes and metal-enriched stars—to cosmic reionization. These will help us to understand the role of magnetic fields, X-rays and space dust in gas cooling, and the identity and behavior of the mysterious dark matter that drives star formation.”