Astronomers have directly detected an extraordinarily faint radio signal from hydrogen gas billions of light-years away, demonstrating a promising new method for mapping the vast structure of the Universe. The international team, led by researchers at the University of Manchester and the University of the Western Cape, used South Africa's MeerKAT radio telescope to measure emissions from neutral hydrogen dating to a period when the Universe was several billion years younger than it is today. Published in The Astrophysical Journal Letters, the results highlight the growing potential of hydrogen intensity mapping, a technique designed to survey enormous regions of space far more efficiently than methods that rely on identifying galaxies individually.
Neutral hydrogen naturally gives off a very weak radio emission known as the 21-centimeter line. Because the Universe is expanding, this signal becomes stretched to longer wavelengths as it travels through space. By measuring that shift, astronomers can study hydrogen from different eras in cosmic history.
Hydrogen intensity mapping takes advantage of this signal in a different way from conventional galaxy surveys. Instead of attempting to identify and measure one galaxy at a time, astronomers detect the combined radio glow produced by hydrogen in large numbers of galaxies that cannot be individually resolved. That approach makes it possible to examine huge volumes of space and reconstruct a three-dimensional view of how matter is distributed across the Universe.
Previous reliable measurements of hydrogen at these distances generally required astronomers to combine radio telescope observations with data from optical galaxy surveys. In this case, the researchers were able to directly identify the hydrogen intensity mapping signal using MeerKAT radio observations by themselves. The researchers examined about 96 hours of MeerKAT observations and found the signal from two separate periods in cosmic history.
The emissions had traveled for approximately four to five billion years before arriving at Earth. The measurements allowed the team to trace hydrogen across distances of several million light-years, roughly comparable to the separation between the Milky Way and the neighboring Andromeda galaxy. "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." Extracting such a weak signal required the researchers to carefully account for many different sources of interference that could distort the measurements.
Extract — continue reading at the source.
