On February 28th, 2018 we learned about

Scientists detect evidence of the first stars ever formed in the universe

As much as the name “Big Bang” seems like it should be noisy and active, early years of the universe were pretty dark, quiet and essentially inert. With no light, vibration or other activity, the only “stuff” out there was a lot of neutral hydrogen gas. Of course, gravity also existed, and over the course of 50  to 100 million years, it clumps of hydrogen started crushing together, eventually leading to the formation of stars, galaxies and critically, electromagnetic radiation in the radio-frequency range. This ancient radiation has now been directly detected, and promises to reveal a lot of new information on how the first stars were formed.

Finding the right frequencies

The radio waves in question were emitted only 180 million years after the universe began, which is relatively quick when looking at an overall timescale of 13.7 billion years. Searches of frequencies originating from earlier time periods found only silence, but once researchers expanded their search a signal was finally detected, although listening in wasn’t easy. The faint murmurs of the first stars were nearly too soft to detect against the background noise of the universe, eliciting comparisons to listening for hummingbirds during a hurricane.

To listen to the signals of the first stars, scientists built a special receiver, called a radio spectrometer.  While it looked a bit more like a table than an antenna, with two metal plates on a set of legs in a larger field of wire mesh, its location in the Australian desert was a critical feature.  By being place at the Murchison Radio-astronomy Observatory, the radio spectrometer would be somewhat insulated from other radio signals thanks legal restrictions on transmissions in the surrounding 161 miles. This gave researchers their best chance at isolating the correct radio signals to find the traces of stars from long ago.

Stars seen as blocked signals

With everything in place, the signals in question are actually pockets of silence. As the primordial hydrogen started clumping up to form stars, it would end up absorbing and blocking some of the background radiation already present in the universe. Learning about the details of those gaps in the signal can then inform use more about the conditions in space when stars started forming. For starters, researchers have already found that the hydrogen gas was apparently colder than previously estimated. This surprising data has already led to interesting models about why temperatures were so low, including the idea that some energy was being lost to interactions with dark matter. To confirm that idea, we’ll need more observations from other instruments to confirm just what was going on “immediately” after the Big Bang.

Source: Unlocking the secrets of the universe by Arizona State University, Phys.org

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