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First stars
This artist’s rendering shows the universe’s first, massive, blue stars embedded in gaseous filaments, with the cosmic microwave background just visible at the edges. (NSF Illustration / N.R. Fuller)

Astronomers have detected radio waves from a time within 180 million years of the Big Bang, and they say they see signs of what may be the first stars to coalesce in the infant universe.

The detection was made using an array of radio antennas that was set up in Australia for a project known as the Experiment to Detect the Global Epoch of Reionization Signature, or EDGES. Astronomers from Arizona, Massachusetts and Colorado reported their discovery in this week’s issue of the journal Nature.

“Finding this minuscule signal has opened a new window on the early universe,” lead investigator Judd Bowman of Arizona State University said in a news release. “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.”

Although the signal was difficult to detect, it was twice as dramatic as computer models predicted for the startup of the first stars. If the findings hold up, the models would have to be adjusted to account for the effect, and one possible explanation could involve interactions with dark matter.

“If that idea is confirmed, then we’ve learned something new and fundamental about the mysterious dark matter that makes up 85 percent of the matter in the universe,” Bowman said. “This would provide the first glimpse of physics beyond the standard model.”

Some astronomers counseled caution.

Harvard theoretical astrophysicist Avi Loeb told The Associated Press that if the observations are fully verified, the discovery “deserves two Nobel Prizes” — one for finding the signature of the first stars, and the other for gaining insights into dark matter.

However, he noted that such extraordinary claims require extraordinary evidence. “What makes me a bit nervous is the fact that the [signal] doesn’t look like what we expected,” Loeb told Science News.

The signal consists of radio emissions associated with the earliest stars during phases of the universe’s history known as the cosmic dawn and the epoch of reionization.

When the first stars fired up, they sent out a blast of ultraviolet light that interacted with the surrounding hydrogen gas. Specific frequencies of light were absorbed by hydrogen atoms, causing a telltale change in the pattern of emissions.

Bowman and his colleagues looked for characteristic dips in frequencies of cosmic background radiation that should have been affected by the ultraviolet blast. But it wasn’t easy: Models predicted that the dips would be found in wavelengths between 65 MHz and 95 MHz, a range that overlaps FM radio frequencies and radio emissions from the center of our Milky Way galaxy.

“Sources of noise can be 10,000 times brighter than the signal,” said Peter Kurczynski, a program officer at the National Science Foundation who oversaw funding for the EDGES project. “It’s like being in the middle of a hurricane and trying to hear the flap of a hummingbird’s wing.”

Starting more than a decade ago, astronomers designed and built the EDGES antenna system to get a clear fix on the target wavelengths from a vantage point at the Murchison Radio-astronomy Observatory in Western Australia.

The signal was first detected in 2015, and since then, the astronomers have been rechecking their data to validate the detection.

Cosmic timeline
This updated timeline of the universe reflects the recent discovery that the first stars emerged by 180 million years after the Big Bang. Click on the image for a larger version. (NSF Illustration / N.R. Fuller)

The pattern of the radio signal seems to suggest that the hydrogen gas in the early universe was much colder than expected. That implies that there could be something amiss about the observations, or that a significant effect hasn’t been accounted for.

In a separate paper published by Nature, Tel Aviv University’s Rennan Barkana proposes that the hydrogen atoms slowly lost their energy through interactions with dark matter. If confirmed, that would serve as the earliest evidence for the existence of dark matter, a substance that is still poorly understood.

The findings are likely to spark debate among other astronomers, and a rush to confirm or refute the observations using other instruments.

Bowman said he’d welcome such efforts. “We worked very hard over the last two years to validate the detection,” he said in an ASU news release, “but having another group confirm it independently is a critical part of the scientific process.”

Clearer signals could be detected by radio telescopes such as the Hydrogen Epoch of Reionization Array, or HERA, in South Africa; and the Owens Valley Long Wavelength Array, or OVRO-LWA, in California.

In addition to Bowman, the authors of the Nature paper, titled “An Absorption Profile Centred at 78 Megahertz in the Sky-Averaged Spectrum,” include Alan Rogers, Raul Monsalve, Thomas Mozdzen and Nivedita Mahesh. The research was supported by NSF awards AST-0905990AST-1207761, and AST-1609450, amounting to $1.64 million.

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