The international MeerKLASS project has reported the first measurement of the large-scale distribution of cosmic hydrogen. The work was published in the journal Monthly Notices of the Royal Astronomical Society. The result is important for cosmology - the science of the structure and evolution of the Universe.
The researchers used data from the MeerKAT radio telescope in South Africa obtained during the MeerKLASS survey. To detect the signal, they used the 21-cm intensity mapping method. It combines hydrogen emission from many galaxies over large areas of sky, making it possible to see the overall pattern even when individual galaxies cannot be distinguished. This makes it possible to build a three-dimensional map of the Universe.
The signal traveled to us for about 4.5 billion years: at that epoch the age of the Universe was slightly more than 9 billion years. The observations covered approximately 250 square degrees of sky - about 1,250 patches the size of the full Moon.
The main difficulty is isolating the weak signal against the background of interference. The astrophysical "foreground" emission (light from other sources along the signal's path) is many times stronger than the hydrogen signal. According to the authors, this is akin to trying to make out a whisper in the front row of a rock concert.
The team used a new observing mode: instead of combining 64 antennas into a single interferometer (a system that works as one large antenna), each dish was used as an independent telescope. In exchange for image sharpness, they gained a high survey speed. Many independent maps were compared with one another: the real cosmic structure repeats, while differences in instrument performance are suppressed. This made it possible to confirm a signal exceeding the statistical noise by more than a factor of six.
"This is a milestone in the establishment of 21-cm intensity mapping as a new tool for cosmology," said the head of the MeerKLASS survey, Professor Mario Santos of the University of the Western Cape. "The measurement required ten years of patient work by researchers from seven countries on three continents."
Dr Steven Cunnington of the University of Portsmouth led the development of the analysis pipeline that made it possible to detect the signal. According to him, the result is especially important because the path began with his doctoral dissertation more than ten years ago.
The scientists emphasize that this is the first measurement of its kind, and that checks and refinements lie ahead. The work demonstrates the potential of the method, but does not mean that a map of the Universe has already been built.