Astronomers using South Africa’s MeerKAT radio telescope have directly detected faint neutral hydrogen gas across billions of light-years without relying on external optical surveys. Published in The Astrophysical Journal Letters, the milestone demonstrates hydrogen intensity mapping as a practical cosmological tool for charting the large-scale structure of the universe, and to probe the dark matter and dark energy that shape it.
An international team of astronomers from the University of the Western Cape (UWC) and the University of Manchester achieved the breakthrough by analyzing approximately 96 hours of MeerKAT observations. The telescope captured signals from two periods in cosmic history, corresponding to redshifts of about 0.32 and 0.44. This means the emission travelled for roughly four to five billion years before reaching Earth, tracing hydrogen over scales of a few megaparsecs—a few times the distance between our Milky Way and its neighbouring galaxy, Andromeda.
Technical Readiness and Unexpected Discoveries
The data driving this discovery carry a notable provenance. According to Dr. Fernando Camilo, SARAO’s chief scientist, the underlying observations were obtained in 2018 before MeerKAT had started science operations. We obtained these data to demonstrate the technical readiness of the telescope, not with any particular scientific goal in mind,
he explained. Since then, however, this exquisite dataset has been used to investigate the star formation history of the universe, and now has also been used to demonstrate the power of the intensity mapping method to map the deep Universe.
In a parallel development highlighting the instrument’s capabilities, researchers operating the same telescope uncovered a hydroxyl megamaser. A team including Thato Manamela, a postdoctoral researcher at the University of Pretoria, and Roger Deane, director of the Inter-University Institute for Data Intensive Astronomy and a professor at the universities of Cape Town and Pretoria, detected the most distant hydroxyl megamaser ever detected, located in a violently merging galaxy more than 8 billion light-years away.
While targeting neutral hydrogen, MeerKAT’s wide bandwidth enabled the surprise discovery of the megamaser signal in the same data. Gravitational lensing boosted the signal enough to detect it, enabling a rapid detection in just five hours of observing time that typically requires hundreds of hours of observation, given its distance and rarity.
Overcoming Faint Signals and Cosmic Contamination
Isolating the natural 21-centimetre line emitted by neutral atomic hydrogen presents severe technical hurdles. The signal is extremely faint and difficult to isolate from foreground emission, human-made radio-frequency interference, and instrumental effects.
This was a challenging data analysis process, requiring a detailed understanding of the many sources of contamination that can affect such a faint measurement,
said Prof. Mario Santos, who is also affiliated with the South African Radio Astronomy Observatory (SARAO) which built and operates MeerKAT in the Karoo region of the Northern Cape.
The project was initiated in 2021 at the University of the Western Cape, while Dr Sourabh Paul was a postdoctoral researcher in the group of Prof. Mario Santos.
Implications for Future Global Radio Astronomy
Rather than detecting individual galaxies one by one, hydrogen intensity mapping measures the combined emission from many unresolved galaxies at once, making it a powerful way to survey very large volumes of the Universe efficiently. Until now, robust detections of this signal at these distances have typically relied on combining radio observations with optical galaxy surveys.
“This is a very exciting milestone,” said Dr Sourabh Paul, lead author of the study. “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. Detecting it directly with MeerKAT shows that this technique is becoming a practical tool for cosmology.”
These capabilities serve as a preview of what the upcoming Square Kilometre Array (SKA), a unique, one-of-a-kind international mega-project, might achieve. The SKA Observatory (SKA-Low and SKA-Mid) focuses on low-to-mid radio frequencies. Meanwhile, a highly complementary next-generation facility called the next-generation Very Large Array (ngVLA) is being planned and designed for construction in the US to operate at much higher frequencies, forming two of the major pillars of next-generation global radio astronomy.
Ещё по этой теме
