Here’s what you’ll learn when you read this story:
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About a billion years after the Big Bang, the universe experienced a period known as the “epoch of reionization,” where neutral hydrogen atoms filling the universe became ionized by ultraviolet light from the first stars.
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Now, a new study wants to understand the conditions of the universe right at the end of the “cosmic dark ages” before this reionization began.
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Using a decade of data from the Murchison Widefield Array telescope located in Western Australia, the researchers determined that reionization did not have a “cold start” and that warming, likely due to black holes and stellar debris, probably began about 800 million years after the Big Bang.
Everyone is familiar with the explosive beginnings of our universe: things got very hot and In fact dense until there was a Big Bang. However, the sequel to this explosive preamble has a decidedly different tone. After the Big Bang, the universe cooled and expanded rapidly until finally (400,000 years later) protons and electrons fused to form hydrogen atoms.
As Live Science notes, what followed is known as the “cosmic dark ages,” when the universe was filled with this neutral hydrogen for about a billion years until the arrival of the first stars and galaxies. Once these primordial stars emitted ultraviolet light that stripped hydrogen atoms of their electrons, the cosmos entered the “Reionization epoch“And the universe began to look like what we imagine today. These are the early days of the universe, so to speak.
However, unlike an obsessive parent documenting every milestone of his drooling progeny, astrophysicists don’t have as much evidence; instead, they have to go find it. For example, we don’t really know what the conditions of the universe were when the “cosmic dark ages” transition began. While some theories suggest that reionization developed from a “cold start,” a new study from an international team of scientists provides evidence that the universe was actually warming before this important milestone in its development. The results of the study were published in The Astrophysical Magazine.
“As the universe evolves, the gas between galaxies expands and cools, so we would expect it to be very, very cold,” Cathryn Trott of Curtin University, lead author of the study, said in a press release. “Our measurements show that it at least warms to some extent. Not much, but this tells us that very cold reionization is ruled out.”
Glimpsing something so distant in the past is not easy, and Trott and his team used the Murchison Widefield Array telescope located in Western Australia to facilitate the challenging observation. Operating at 70-300 MHz, the telescope is specifically designed to detect the aforementioned “reionization epoch” neutral hydrogen emission. Still, the authors needed to do a lot of subtraction to isolate what they were looking for from the cosmic noise of nearby stars, galaxies, and even Earth’s atmosphere.
Because the team was able to create this leaked data, in addition to having the benefit of ten years worth it: they could make a discovery by omission. If the universe were cold at that time, it would emit some kind of signal, but the researchers found no evidence of this, suggesting that at least some warming was happening. The theory is that X-rays from early black holes and stellar debris drove this warming about 800 million years after the Big Bang. They haven’t yet found the telltale sign of that warming, but researchers say it’s probably just a matter of time.
“All of these existing techniques will help us find what’s missing,” Ridhima Nunhokee, co-author of the study from Curtin University, said in a press release. “The signal is definitely buried there. It’s just improving our data and getting more data, cleaner data, to get to it.”
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