Scientists discover radio signals from 9 billion light-years away
Scientists have captured radio signals from a galaxy almost 9 billion light-years away from the Earth,. This is the first time a signal like this has been received from such a distance.
Scientists detected the signals by a unique wavelength known as a “21-centimetre line” or the “hydrogen line,” which is reportedly emitted by neutral hydrogen atoms.
The radio frequency signal was picked up by the Giant Metrewave Radio Telescope (GMRT) in India, and originated in the galaxy SDSSJ0826+5630, located 8.8 billion light-years from Earth. That means the signal was emitted when our 13.8-billion-year-old universe was roughly a third of its current age.
The telescope was able to pick up the distant signal because it was bent by another galaxy located between the signal and the telescope, researchers said. “This effectively results in the magnification of the signal by a factor of 30, allowing the telescope to pick it up,” said Nirupam Roy, co-author of the study and an associate professor at the Indian Institute of Science (IISc).
“The astronomical distance over which such a signal has been picked up is the largest so far by a large margin. This is also the first confirmed detection of strong lensing of 21 cm emission from a galaxy”, according to a statement from Indian Institute of Science.
The findings have been published in Monthly Notices of the Royal Astronomical Society.
Atomic hydrogen is the basic fuel required for star formation in a galaxy. When hot ionised gas from the surrounding medium of a galaxy falls onto the galaxy, the gas cools and forms atomic hydrogen, which then becomes molecular hydrogen, and eventually leads to the formation of stars, it was explained.
“Therefore, understanding the evolution of galaxies over cosmic time requires tracing the evolution of neutral gas at different cosmological epochs”, the statement said.
Atomic hydrogen emits radio waves of 21 cm wavelength, which can be detected using low-frequency radio telescopes like the GMRT. Thus, 21 cm emission is a direct tracer of the atomic gas content in both nearby and distant galaxies, the PTI report said.
However, this radio signal is extremely weak and it is nearly impossible to detect the emission from a distant galaxy using current telescopes due to their limited sensitivity.
“Until now, the most distant galaxy detected using 21 cm emission was at redshift z=0.376, which corresponds to a look-back time – the time elapsed between detecting the signal and its original emission – of 4.1 billion years (Redshift represents the change in wavelength of the signal depending on the object’s location and movement; a greater value of z indicates a farther object),” it said.
“Due to the immense distance to the galaxy, the 21 cm emission line had redshifted to 48 cm by the time the signal travelled from the source to the telescope,” says Arnab Chakraborty, a post-doctoral researcher at the Department of Physics and Trottier Space Institute of McGill University. 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.
This detection was made possible by a phenomenon called gravitational lensing, in which the light emitted by the source is bent due to the presence of another massive body, such as an early type elliptical galaxy, between the target galaxy and the observer, effectively resulting in the “magnification” of the signal.
“In this specific case, the magnification of the signal was about a factor of 30, allowing us to see through the high redshift universe,” explains Roy.
The team also observed that the atomic hydrogen mass of this particular galaxy is almost twice as high as its stellar mass. These results demonstrate the feasibility of observing atomic gas from galaxies at cosmological distances in similar lensed systems with a modest amount of observing time. It also opens up exciting new possibilities for probing the cosmic evolution of neutral gas with existing and upcoming low-frequency radio telescopes in the near future, the statement said.
Part of the article was reported by NDTV.