The \u201cEpoch of Reionization\u201d was a critical period for cosmic evolution and has always fascinated and mystified astronomers. During this epoch, the first stars and galaxies formed and reionized the clouds of neutral hydrogen that permeated the Universe. This ended the Cosmic Dark Ages and led to the Universe becoming \u201ctransparent,\u201d what astronomers refer to as \u201cCosmic Dawn.\u201d According to our current cosmological models, reionization lasted from 380,000 to 1 billion years after the Big Bang. This is based on indirect evidence since astronomers have been unable to view the Epoch of Reionization directly. <\/p>\n
Investigating this period was one of the main reasons for developing the James Webb Space Telescope<\/em> (JWST), which can pierce the veil of the \u201cdark ages\u201d using its powerful infrared optics. However, observations provided by Webb <\/em>revealed that far more galaxies existed in the early Universe than previously expected. According to a recent study, this suggests that reionization may have happened more rapidly and ended at least 350 million years earlier than our models predict. Once again, the ability to peer into the early Universe has produced tensions with prevailing cosmological theories.<\/p>\n <\/p>\n The study was led by Julian B Mu\u00f1oz, an assistant professor of astronomy at The University of Texas at Austin. He was joined by John Chisholm, also an assistant professor of astronomy at UT Austin; Jordan Mirocha, a NASA postdoctoral student at NASA\u2019s Jet Propulsion Laboratory and the California Institute of Technology; Steven R Furlanetto, an associate professor of physics and astronomy at the University of California-Los Angeles, and Charlotte Mason, an associate professor with the Cosmic Dawn Center at the Niels Bohr Institute. The paper that describes their findings was published in the Monthly Notices of the Royal Astronomical Society.<\/em><\/p>\n According to current cosmological models, the Universe was filled with a hot, dense plasma of protons and electrons for the first 380,000 years after the Big Bang. Eventually, the Universe cooled enough for protons and electrons to come together and form neutral hydrogen. By ca. 100 million years after the Big Bang, the first stars (Population III) began to form, which were extremely massive and hot. These stars came together to create the first galaxies, and their ultraviolet light caused neutral hydrogen to once again split into protons and electrons (aka. became ionized).<\/p>\n Once most of the hydrogen in the Universe became ionized (ca. 1 billion years after the Big Bang), the Epoch of Reionization ended. At this point, the Universe was transparent, and light from this period is visible to optical telescopes today. As Chisholm indicated in a UT Austin news release, reionization also played a major role in how the Universe evolved. \u201cThe process heated and ionized gas in the Universe, which regulated how fast galaxies grew and evolved,\u201d \u201cThese early stars established the overall structure of galaxies in the Universe.\u201d <\/p>\n Before the deployment of the JWST, scientists relied on measurements of the Cosmic Microwave Background (CMB), the relic radiation from the Big Bang, and the Lyman-alpha Forest \u2013 the wavelength of light associated with hydrogen reionization. From this, astronomers have gained a sense of how much energy was available for reionization to occur (a \u201cphoton budget\u201d) and how long it lasted. As Mu\u00f1oz explained:<\/p>\n \u201c[Reionization] is the last major change to happen. You went from neutral and cold and boring to ionized and hot. And this isn\u2019t something that only happened to one or two galaxies. It happened to the whole Universe. It\u2019s an accounting game. We know that all hydrogen was neutral before reionization. From there, you need enough extreme ultraviolet to split each atom. So, at the end of the day, you can do the math to figure out when reionization ended.\u201d<\/em><\/p>\n<\/blockquote>\n However, observations made with the JWST have revealed things that challenge accepted models. This includes a greater abundance of galaxies, which produce more UV radiation than previously anticipated. These findings suggest that reionization should have ended 550 to 650 million years after the Big Bang rather than 1 billion years. But if this were true, the CMB and Lyman-alpha Forest would look different. In short, there is a tension between these measurements and Webb<\/em>\u2018s observations \u2013 as the team describes in their study, a \u201cphoton budget crisis.\u201d <\/p>\n Much like the Hubble Tension, these findings suggest something could be missing from our current cosmological models. One possibility that the team explored is recombination, where ionized protons and electrons come together again to form neutral hydrogen. This is precisely what happened 380,000 years after the Big Bang, known as the \u201cEra of Recombination.\u201d If this process happened more often than our models suggest, it could increase the amount of extreme-UV light needed to reionize the Universe. As Mu\u00f1oz explained, follow-up observations are needed to confirm this theory:<\/p>\n \u201cWe need more detailed and deeper observations of galaxies, and a better understanding of the recombination process. Resolving this tension on reionization is a key step to finally understanding this pivotal period. I am excited to see what the coming years hold.\u201d<\/em><\/p>\n<\/blockquote>\n Further Reading: Phys.org, MNRAS<\/em><\/p>\n\n
![\"Cosmic](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2007\/05\/2007-0507cmbr.jpg\")
\n
Like this:<\/h3>\n