Astronomers have directly detected an extraordinarily faint radio signal from neutral hydrogen gas located billions of light-years away, originating from a period when the cosmos was several billion years younger than its current age of 13.8 billion years. The international team used the MeerKAT radio telescope, which is made up of 64 antennas located in the Karoo region of South Africa’s Northern Cape, to measure emissions that can help researchers map the large-scale structure of the Universe.
Astronomers Directly Detect Ancient Hydrogen Signal
The research, published in the July edition of The Astrophysical Journal Letters, was led by scientists including team leader Sourabh Paul and co-author Zhaoting Chen. Previous reliable measurements of hydrogen at such distances typically required astronomers to combine radio telescope observations with optical galaxy surveys. In this new work, the team successfully identified the signal using MeerKAT radio observations by themselves.
How Hydrogen Intensity Mapping Works
The technique relies on charting where hydrogen, which is the universe’s lightest and most abundant element, is located across space. Neutral hydrogen emits a faint radio signal at a wavelength of 21 centimeters, known as the 21-centimeter line. As the Universe expands, this signal undergoes the redshift effect, allowing astronomers to study hydrogen from different eras in cosmic history based on how much the radiation has been stretched.
Hydrogen intensity mapping differs from conventional galaxy surveys by avoiding the need to identify and measure one galaxy at a time. Instead, researchers detect the cumulative radio glow produced by hydrogen across vast volumes of space. This collective measurement makes it possible to examine huge volumes of space and reconstruct a three-dimensional view of how matter is distributed across the Universe.
Overcoming Data Challenges in 96 Hours of Observations
The international team analyzed approximately 96 hours of MeerKAT observations and extracted signals from hydrogen that had been traveling toward Earth for 4 billion to 5 billion years. These structures span distances of many millions of light-years, comparable to the distance between the Milky Way and the Andromeda galaxy. Remarkably, the data used in the study were gathered in 2018 when the MeerKAT radio telescope had only just started science operations.
Isolating the signal required overcoming significant technical obstacles. Hydrogen intensity mapping has long been seen as a promising way to map the Universe efficiently, but the signal is extremely faint and difficult to isolate from foreground emission, human-made radio-frequency interference, and instrumental effects,
team leader Sourabh Paul stated. Team member Mario G. Santos of the University of the Western Cape noted that the data analysis process required a detailed understanding of the many sources of contamination that can affect such a faint measurement.
Implications for Galaxy Evolution and Future Telescopes
According to the researchers, the successful detection establishes intensity mapping as a practical tool for cosmology. Neutral hydrogen serves as a key ingredient for understanding how galaxies form and evolve. By measuring the collective signal rather than individual objects, scientists gain a new method to study both galaxy evolution and the underlying matter distribution of the cosmos.
The achievement also holds major implications for upcoming cosmological surveys and the Square Kilometre Array Observatory (SKAO), which is under construction in Western Australia and South Africa. MeerKAT serves as a precursor telescope for the SKAO facility, and future studies observing larger portions of the sky for longer periods are expected to allow astronomers to map neutral hydrogen with even greater precision.
