As teams of observers try to replicate those findings in the few places on Earth that are relatively undisturbed by radio interference, theorists are struggling to make sense of the signal. “The signal does not look like anything we expected”, says Abraham Loeb, an astrophysicist at Harvard University in Cambridge, Massachusetts.
Researchers are heading to some of the most remote spots on Earth — from the Tibetan Plateau to an island in the sub-Antarctic ocean — to try to capture an enigmatic radio signal from the early Universe reports today’s Nature.
This grand search, which could even involve a mission to the Moon, includes some of the first experiments to follow up on a surprise announcement in February that astronomers had seen evidence of the Universe’s first stars lighting up, a moment known as the cosmic dawn.
“Finding this minuscule signal has opened a new window on the early universe,” said Judd Bowman of Arizona State University, whose team set out to make the detection more than a decade ago reports The Guardian. “It’s unlikely we’ll be able to see any earlier into the history of stars in our lifetime.”
“Telescopes cannot see far enough to directly image such ancient stars, but we’ve seen when they turned on in radio waves arriving from space,” added Bowman.
An artist’s impression of the universe’s first, massive, blue stars embedded in gaseous filaments is shown above, with the cosmic microwave background just visible at the edges. (NR Fuller, National Science Foundation)
The LEDA experiment in California’s Owens Valley shown below, is one of many experiments trying to probe the first few hundred million years of cosmic history. (Danny C. Price)
The original detection was reported by researchers at the Experiment to Detect the Global Epoch of Reionization Signature (EDGES), using a pair of deceptively simple, table-sized radio antennas in the Australian outback. The experiment measures the long-wavelength part of the cosmic microwave background, the noisy afterglow of the Big Bang. The researchers were searching for a subtle dip in the background spectrum where the microwave radiation is slightly dimmed. Cosmologists have theorized that such a dip should have been caused by the light of the first stars, which made primordial hydrogen in the Universe less transparent at a particular radio wavelength. The details of this absorption should contain information about the early interstellar matter and the stars that cast light on it.
But the blip had an unexpected shape. It suggested that the absorption started to ramp up rapidly around 150 million years after the Big Bang, stayed roughly constant between 200 million and 250 million years ago and then disappeared relatively quickly. The dip was also deeper than predicted, which implied that the gas was colder than expected during that epoch — perhaps 4 kelvin instead of 7 kelvin.
The EDGES team spent two years cross-checking their peculiar result before it decided to go public. “The reason you publish a paper is to bring a lot more minds to bear on a problem that you can’t do on your own,” says EDGES lead scientist Bowman.
Researchers have posted dozens of preprints since, trying to interpret the anomaly. Some physicists have suggested that it was a possible sign of previously undiscovered interactions between ordinary matter and dark matter2. Others saw the opposite: a possible indication of the absence of dark matte.
With theory at an impasse, experimentalists are trying to collect fresh data from remote sites on four continents, often using antennas built on a shoestring budget. Some could have their first results in months.
via The Daily Galaxy