The Universe cooled faster than we thought, possibly due to weird form of dark matter.
Ars Technica said:Today, a small team of researchers is announcing that its correspondingly small telescope picked up something that theoreticians had only suggested might exist: a signal produced by the very first stars in our Universe. Their radiotelescope, only two meters across, didn't image the stars directly. Instead, it picked up an imprint on the Cosmic Microwave Background left by the matter that these stars interacted with.
And, while the signal had been predicted by theoreticians, calculations had suggested that it would be substantially smaller than it actually is. If the results hold up, then it could be a sign that dark matter looks very different from what we had expected.
Ignition
The Cosmic Microwave Background was produced when the Universe cooled enough to allow electrons to settle down into the Universe's first atoms, releasing radiation as they did. It famously captures the state of the Universe when it was formed, telling us about the Big Bang that produced it, as well as the composition of the Universe's contents. But in many ways, it's the gift that keeps giving, as subtle details in the Background provide further details of the Universe's physics, and theorists regularly think up ways to extract more information from it.
Theoretical considerations helped motivate the EDGES project, or Experiment to Detect the Global Epoch of reionization Signature. In an era of massive telescopes, EDGES is refreshingly simple: its largest component is just a 30-meter square of metal plates on the ground. At the center sit two radio antennae sensitive to a specific region of the spectrum that overlaps with part of the Cosmic Microwave Background.
That area of the spectrum has been predicted to capture a rather indirect interaction of the Cosmic Microwave Background and the first stars. At the time the Cosmic Microwave Background was formed, the Universe was still extremely hot and dense, with the first atoms at roughly the same temperature as the radiation they were producing. This allowed them to interact with the Microwave Background radiation for a time, but that time came to an end as the Universe continued to expand and the atoms cooled down.
The ignition of the first stars produced lots of high-energy radiation that heated up the surrounding gas, temporarily pushing it back up to the threshold where it could interact again with the Cosmic Microwave Background. These interactions would reduce the amount of Background radiation in a specific area of the spectrum (currently in the radio wavelengths), with the precise details of the reduction depending on the state of the gas at the time. The EDGES observatory was designed for a single purpose: examine that area of the spectrum.
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The detection itself is an impressive feat and will help verify our theoretical models of the conditions of the Universe when the first stars were formed. But, as mentioned above, the signal also contains information about those conditions. And that information is pretty weird.
The amount of energy absorbed is going to be related to the temperature of the Universe's gas at the time the first stars ignited. And here, the data provides a bit of a surprise: the absorption was twice the amount predicted by even the more extreme models of the early Universe. That means that the gas present in the Universe cooled much faster than we had expected.
Why is that weird? Because almost everything we know about in the Universe was hot at the time. There is no obvious mechanism to cool the gas down.
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