When you sweep across the FM radio band, you don’t always hear music—mostly, you hear static. Lots of this ambient noise is actually garbled signals from throughout the Milky Way. If you had perhaps the most sensitive FM receiver on Earth, you might pick up the tiniest dip in volume: a signal that comes not from our galaxy, but from the earliest stars in the Universe.A team of scientists at the University of Arizona and MIT are reporting today the first observation of a long-predicted radio signal coming from stars formed just a hundred million years after the Big Bang. It’s only initial evidence, and further hunting might change our interpretation of what it means. But it’s a crucial step that could have important implications for telling the story of the early universe.
“After all of the steps over two years, we’re left now with no instrumental explanation—this is truly from the sky,” Judd Bowman, the study’s first author from Arizona State University, told Gizmodo. “It’s a very difficult measurement with a faint signal, and this is the first time that anyone is claiming to see it.”
The observation is basically just a teeny dip in the amplitude of ambient radio waves coming from the lowest part of the FM band. That dip carries lots of meaning.
A radio wave signature from hydrogen, the most common element and building block of stars, permeates the universe. Hydrogen consists of two particles, an electron and a proton, each with a property called “spin” whose values can be “up” or “down.” If the spins are the same, the atom has slightly more energy than if they’re opposite—so if the electron spin flips from parallel to anti-parallel, the atom releases a blip of light with a frequency of around 1.5 GHz. Those light waves are stretched as they travel to us through space, due to the expansion of the universe. The further we look back in time, the more stretched the light is—so older hydrogen emits a longer wavelength than newer hydrogen.
Observing changes and fluctuations to this ever-present signal could reveal new insights about what was going on in the earliest years of the universe, especially the first several hundred million years after the Big Bang, which is mostly invisible to modern telescopes. In these regions, the hydrogen signature has been stretched to frequencies of 50 MHz and 100 MHz—a radio band that mostly encompasses the FM band’s 88 MHz to 101 MHz. Centered around 78MHz, the researchers spotted a slight dip in the amplitude of these waves using a radio antennae in Australia called the Experiment to Detect the Global Epoch of Reionization Signature, or EDGES.
source: Gizmodo.com byRyan F. Mandelbaum