ASU-led team uses radio astronomy to answer questions that astrophysicists have long pondered
Long ago, about 400,000 years after the beginning of the universe —the Big Bang — the universe was dark. There were no stars or galaxies, and the universe was filled primarily with neutral hydrogen gas.
Then, for the next 50 million-100 million years, gravity slowly pulled the densest regions of gas together until they collapsed in some places to form the first stars.
What were those first stars like and when did they form? How did they affect the rest of the universe? These are questions astronomers and astrophysicists have long pondered.
Now, after 12 years of experimental effort, a team of scientists, led by Arizona State University School of Earth and Space Exploration astronomer Judd Bowman, has detected indications of the earliest stars in the universe. Using radio signals, the detection provides the first evidence for the oldest ancestors in our cosmic family tree, born a mere 180 million years after the universe began.
“There was a great technical challenge to making this detection, as sources of noise can be a thousand times brighter than the signal — it’s like being in the middle of a hurricane and trying to hear the flap of a hummingbird’s wing,” said Peter Kurczynski, the National Science Foundation program officer who supported this study. "These researchers with a small radio antenna in the desert have seen farther than the most powerful space telescopes, opening a new window on the early universe.”
To find these fingerprints, Bowman’s team used a ground-based instrument called a radio spectrometer, located at the Australian national science agency's (CSIRO) Murchison Radio-astronomy Observatory (MRO) in Western Australia. Through their Experiment to Detect the Global EoR Signature (EDGES), the team measured the average radio spectrum of all the astronomical signals received across most of the Southern Hemisphere sky and looked for small changes in power as a function of wavelength (or frequency).
As radio waves enter the ground-based antenna, they are amplified by a receiver, and then digitized and recorded by computer, similar to how FM radio and TV receivers work. The difference is that the instrument is very precisely calibrated and designed to perform as uniformly as possible across many radio wavelengths.
The signals detected by the radio spectrometer in this study came from primordial hydrogen gas that filled the young universe and existed between all the stars and galaxies. These signals hold a wealth of information that opens a new window on how early stars — and later, black holes and galaxies — formed and evolved.
“It is unlikely that we’ll be able to see any earlier into the history of stars in our lifetimes,” said Bowman. “This project shows that a promising new technique can work and has paved the way for decades of new astrophysical discoveries.”
This detection highlights the exceptional radio quietness of the MRO, particularly as the feature found by EDGES overlaps the frequency range used by FM radio stations. Australian national legislation limits the use of radio transmitters within 161.5 miles (260 km) of the site, substantially reducing interference that could otherwise drown out sensitive astronomy observations.