Astronomers capture radio signal from distant galaxy

Giant Metrewave Radio Telescope
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Giant VHF radio telescope

One of the dishes of the Giant Metrewave Radio Telescope (GMRT) near Pune, Maharashtra, India. Credit: National Center for Radio Astrophysics

Exploring galaxies at much greater distances from Earth may now be within reach.

How do stars form in distant galaxies? Astronomers have long been trying to answer this question by detecting radio signals emitted by nearby galaxies. However, these signals get weaker the farther a galaxy is from Earth, making it harder for today’s radio telescopes to detect them.

Now, researchers from Montreal and India have captured a radio signal from the most distant galaxy yet at a specific wavelength known as the 21cm line, allowing astronomers to peer into the secrets of the early universe. With the help of the Giant VHF Radio Telescope in India, this is the first time this type of radio signal has been detected at such a great distance.

Signal detection from a distant galaxy

Illustration showing the detection of the signal from a distant galaxy. Credit: Swadha Pardesi

“A galaxy emits different types of radio signals. Until now, it has only been possible to capture this particular signal from a nearby galaxy, limiting our knowledge to those galaxies closest to Earth,” says Arnab Chakraborty, a postdoctoral researcher at McGill University under the supervision of Professor Matt Dobbs.

“But thanks to the help of a natural phenomenon called gravitational lensing, we can capture a weak signal from a record distance. This will help us understand the composition of galaxies at much greater distances from Earth,” he adds.

A look back in time to the early universe

For the first time, the researchers were able to detect the signal from a distant star-forming galaxy known as SDSSJ0826+5630 and measure its gaseous composition. The researchers observed that the atomic mass of the gas content of this particular galaxy is almost twice the mass of the stars visible to us.

Radio signal from a distant galaxy

Radio signal image of the galaxy. Credit: Chakraborty & Roy/NCRA-TIFR/GMRT

The signal detected by the team was emitted from this galaxy when the universe was only 4.9 billion years old, giving researchers a glimpse into the secrets of the early universe. “It’s the equivalent of looking back 8.8 billion years,” says Chakraborty, who studies cosmology in McGill’s Department of Physics.

Picking up the signal from a distant galaxy

“Gravitational lensing magnifies the signal coming from a distant object to help us observe the early universe. In this specific case, the signal is deflected by the presence of another massive body, another galaxy, between the target and the observer. This effectively results in magnifying the signal by a factor of 30, allowing the telescope to pick it up,” says co-author Nirupam Roy, Associate Professor in the Department of Physics at the Indian Institute of Science.

According to the researchers, these results demonstrate the feasibility of observing distant galaxies in similar situations with gravitational lensing. It also opens up exciting new opportunities to investigate the cosmic evolution of stars and galaxies with existing low-frequency radio telescopes.

Reference: “Detection of 21 cm HI emission from a strongly lensed galaxy at z ∼ 1.3” by Arnab Chakraborty and Nirupam Roy, 23 Dec 2022, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stac3696

The Giant VHF Radio Telescope was built and is operated by NCRA-TIFR. The research was funded by McGill University and the Indian Institute of Science.

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