Astronomers just detected the furthest atomic hydrogen signal ever

It is the most distant atomic hydrogen radio signal "by a large margin" and it could teach us a great deal about star formation.
Chris Young
Giant Metrewave Radio Telescope
Giant Metrewave Radio Telescope


Astronomers from McGill University in Canada and the Indian Institute of Science (IISc) in Bengaluru detected an atomic hydrogen radio signal originating 8.8 billion light-years from Earth.

This makes it the most distant atomic hydrogen radio signal ever observed, a press statement reveals. They pinpointed the signal — with the aid of gravitational lensing — in data from the Giant Metrewave Radio Telescope (GMRT) in Pune, India.

As the statement points out, "this is also the first confirmed detection of strong lensing of 21 cm emission from a galaxy."

Scientists use gravitational lensing to detect the most distant atomic hydrogen radio signal

The 21 cm emission, also known as the hydrogen line, refers to the electromagnetic spectral line created by a change in the energy state of neutral hydrogen atoms. In other words, it is a signal that acts as a telltale sign of atomic hydrogen. It is detectable by low-frequency radio telescopes.

The researchers, who published their findings in a paper in the Monthly Notices of the Royal Astronomical Society, detected the faint signal using a combination of the Giant Meterwave Radio Telescope and gravitational lensing.

Gravitational lensing occurs when a massive object, such as a galaxy cluster, causes spacetime to curve around it. This curvature acts like a lens for passing light and magnifies distant galaxies, stars, and signals, meaning they can be more easily detected from Earth.

The hydrogen line is extremely weak, and current telescope technology has been able to detect it 4.1 billion light-years away. That's a relatively small distance, given the fact that atomic hydrogen is one of the key ingredients for star formation and is thought to have been abundant in the early universe.

Astronomers just detected the furthest atomic hydrogen signal ever
An illustration showing the detection of the atomic hydrogen signal via gravitational lensing.

The new detection more than doubles the distance. The statement points out the fact that "the signal detected by the team was emitted from this galaxy when the universe was only 4.9 billion years old; in other words, the look-back time for this source is 8.8 billion years." The scientists could detect such a distant signal source thanks to the fact that a large object caused gravitational lensing that magnified part of the image by a factor of 30.

Mapping the distant universe with low-frequency radio telescopes

Atomic hydrogen is the basic fuel required for star formation. It is formed when hot ionized gas surrounding a galaxy cools down. The atomic hydrogen then becomes molecular hydrogen which then goes on to play a crucial role in star formation. The role atomic hydrogen plays in the formation of stars and solar systems means the discovery could prove valuable for scientists looking to better understand the universe's evolution over different cosmological epochs.

Yashwant Gupta, the Center Director at the National Centre for Radio Astrophysics (NCRA) in India, said, "detecting neutral hydrogen in emission from the distant Universe is extremely challenging and has been one of the key science goals of GMRT. We are happy with this new path-breaking result with the GMRT and hope that the same can be confirmed and improved upon in the future."

The team behind the record-breaking atomic hydrogen signal detection also observed that the atomic hydrogen mass in its galaxy is almost double that of its stellar mass. The observation shows the great potential for cataloging distant galaxies and unveiling the mysteries of the early universe using existing and future low-frequency radio telescopes.

This was a developing story, and it was updated as new information emerged.

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