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Did Galaxies Change the Early Universe?

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The team led by Simon Lilly of ETH Zürich in Switzerland recently used NASA’s James Webb Space Telescope to analyze new observations and found evidence that galaxies existing 900 million years after the big bang ionized the gas around them, causing it to become transparent. This process was precisely measured by Webb, which identified that there were “bubbles” of ionized gas with a 2 million light-year radius around the galaxies. Over the next hundred million years, the bubbles continued to grow larger and eventually merged in order to cause the entire universe to become transparent.


The early universe was filled with opaque gas between stars and galaxies that prevented energetic starlight from penetrating it. However, around one billion years after the big bang, the gas had fully become transparent. A team of researchers from ETH Zürich in Switzerland, led by Simon Lilly, utilized data from NASA’s James Webb Space Telescope to pinpoint the reason behind this phenomenon. It was found that the stars in galaxies emitted light strong enough to heat up and ionize the gas around them, effectively making the universe go through a dramatic change called the Era of Reionization. This process began with the cooling of gas in the universe many hundreds of millions of years after the big bang, and was likely caused by the formation of early stars in galaxies.


Researchers have long sought definitive evidence to explain the transformations seen in the universe’s reionization period. With the new results from the James Webb Space Telescope, the curtain has been pulled back to reveal that these transformations are largely driven by galaxies reionizing the gas around them. The transparent regions of gas around galaxies are gigantic compared to their size, being likened to a hot air balloon housing a pea inside. It is these relatively tiny galaxies that are driving the reionization process, creating massive transparent bubbles that grow and merge over hundreds of millions of years, ultimately leading to the universe becoming entirely transparent. Thus, the new results from Webb effectively show how galaxies are responsible for these cosmic transformations.


Was the universe very different 13 billion years ago, during the epoch of reionization?


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More than 13 billion years ago,during the Era of Reionization, the gas between galaxies was largely opaque to energetic light, making it difficult to observe young galaxies. However, a NASA research team recently discovered that galaxies are overwhelmingly responsible for allowing the universe to become completely ionized, leading to the “clear” conditions detected in much of the universe today. This breakthrough sheds light on understanding how galaxies continue to shape the cosmos, even after billions of years of evolution.



Lilly’s team targeted a patchwork of gas in various states just before the end of the Era of Reionization. To study this, they aimed Webb in the direction of a quasar, an illuminated active supermassive black hole. As the light traveled through different patches of gas, it either got absorbed or moved freely through transparent gas. To get the groundbreaking results, they combined Webb’s data with observations from the W. M. Keck Observatory in Hawaii, and the European Southern Observatory’s Very Large Telescope and the Magellan Telescope at Las Campanas Observatory in Chile. The quasar illuminated the gas along their line of sight, giving them extensive information about its composition and state. This data was then used by Anna-Christina Eilers from MIT to get their results.



Utilizing the Webb Telescope, researchers uncovered that galaxies at the end of the Era of Reionization were surrounded by transparent regions of 2 million light-years in radius. This is significant as it is equivalent to the distance between our Milky Way galaxy and our nearest neighbor, Andromeda. By having access to this sight, researchers were able to observe galaxies in the process of clearing the space around them which has been a long debated cause of reionization. The galaxies appear chaotic with active star formation and supernovae, showing that the galaxies had an adventurous youth.


The Universe In the universe only 900 million years old, galaxies were clustered and elongated.


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NASA’s James Webb Space Telescope has returned extraordinarily detailed near-infrared images of galaxies that existed when the universe was only 900 million years old. These distant galaxies display never-before-seen structures that are clumpy and often elongated. What’s more, these galaxies are also actively forming stars, providing further insight into the incredible and dynamic nature of the early universe. This data provides a valuable resource for astronomers who are looking to understand how galaxies evolve and develop over time.



Using data from Webb, Eilers was able to confirm the mass of the black hole in the quasar at the center of the field, which weighed an astonishing 10 billion times that of the Sun. Interestingly, however, Eilers could not explain how quasars were able to grow so large so early in the universe’s history. Through Webb’s exquisite images, she found no evidence that light from the quasar had been gravitationally lensed, so the mass measurements were definitive. Eilers’ work serves as an important step in understanding more about universe and how it came to be.



Lilly’s research team, the Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER), has already made incredible strides in their research using the help of the Near-Infrared Camera from the James Webb Space Telescope (Webb). By combining conventional images from Webb’s NIRCam with data from the same instrument’s wide-field slitless spectroscopy mode, they have been able to use Webb as a “spectacular spectroscopic redshift machine” to identify 117 galaxies from the Era of Reionization – surpassing the expectations of even the researchers. The team is now eager to dive into research about galaxies in five additional fields, each anchored by a central quasar. 


Did Galaxies Change the Early Universe?

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