GMRT Dish (from website)
Imagine hearing a sound from nine billion years ago, at the very least. Well, scientists from India say they have done just that: they detected a radio signal originating from an area of space nine billion light years away from the Earth. The discovery was made by the Giant Metrewave Radio Telescope GMRT in India
OK, so this was not exactly a noise. But it will allow scientists to determine the nature of a faraway galaxy that is still in formation.
Astronomers from McGill University in Canada and the Indian Institute of Science (IISc) in Bengaluru have used data from the Giant Metrewave Radio Telescope (GMRT) in Pune to detect a radio signal originating from atomic hydrogen in an extremely distant galaxy. 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.
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The scientists explained that atomic hydrogen is the basic fuel required for star formation in a galaxy. When hot ionized 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. Therefore, understanding the evolution of galaxies over cosmic time requires tracing the evolution of neutral gas at different cosmological epochs.
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.
Using GMRT data, Arnab Chakraborty, postdoctoral researcher at the Department of Physics and Trottier Space Institute of McGill University, and Nirupam Roy, Associate Professor, Department of Physics, IISc have detected a radio signal from atomic hydrogen in a distant galaxy at redshift z=1.29.
“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 Chakraborty. 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.
“A galaxy emits different kinds of radio signals. Until now, it’s only been possible to capture this particular signal from a galaxy nearby, limiting our knowledge to those galaxies closer to Earth,” Chakraborty added.
