Hydrogen is the most common element in the universe, but the form it takes and where exactly it’s detected can tell us a lot about the universe. Scientists from McGill University in Canada and the Indian Institute of Science (IISc) in Bengaluru have made history by detecting atomic hydrogen in the most distant galaxy ever. The advancement is down to the Giant Metrewave Radio Telescope (GMRT) array with a little help from gravity.
Atomic hydrogen emits radio waves with a wavelength of 21 cm. This signal can be detected throughout the universe, including some very distant regions. Until now, the record for atomic hydrogen detection was 4.1 billion light-years (redshift z=0.376). The Indian-Canadian team has more than doubled that to 8.8 billion light years. That means the signals detected by the GMRT array were emitted when the universe was just 4.9 billion years old.
Hydrogen is the fuel of star formation, and from hydrogen, you can eventually get all the other elements on the periodic table. According to a statement from the IISc, tracing the evolution of neutral gas at different cosmological epochs is essential to understanding the evolution of galaxies. The process starts with hot ionized gas around a young galaxy. As these clouds of gas fall into a galaxy, they cool and become atomic hydrogen (aka neutral hydrogen). From there, it forms molecular hydrogen, which is two hydrogen atoms bonded together. It is this material that coalesces into new stars.
Usually, a 21 cm signal is too faint to detect more than 8 billion light years away, but the team was able to use a phenomenon known as gravitational lensing to extend the reach of the Giant Metrewave Radio Telescope. The effect of gravity around a massive object like a galaxy can magnify light like a telescope lens does. In this case, the researchers were able to spot the 21 cm signal, which, due to the z=1.29 redshift, was 48 cm by the time it reached Earth. They estimate the gravitational lens amplified the signal by a factor of 30. The data also shows that the atomic hydrogen mass of this distant galaxy is twice that of its stellar mass.
The team believes this is just the beginning of distant hydrogen detections. Upcoming low-frequency telescopes could allow similar detections without gravitational lensing, which could confirm and improve upon the data from the GMRT and teach us more about the early universe.
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