Hydrogen is an important building block of the cosmos. Whether reduced to its charged core or stacked into a molecule, the nature of its presence can tell you much about the properties of the Universe at the largest scale.
Because of this, astronomers are very interested in detecting signals from this element wherever it is found.
Now the light signature of uncharged atomic hydrogen has been measured far further from Earth than ever before. The Giant Meterwave Radio Telescope (GMRT) in India picked up a signal with a lookback time – the time between emission and detection of light – of a whopping 8.8 billion years.
This gives us an exciting glimpse into some of the earliest moments in the universe, currently thought to be around 13.8 billion years old.
“A galaxy emits different types of radio signals,” says cosmologist Arnab Chakraborty, from McGill University in Canada. “Until now, it has only been possible to detect this particular signal from a nearby galaxy, limiting our knowledge to the galaxies closer to Earth.”
In this case, the radio signal emitted by atomic hydrogen is a light wave 21 centimeters long. Long waves are not very energetic, nor is the light intense, making it difficult to see from afar; the Lookback time of the previous record was only 4.4 billion years.
Due to the great distance it traveled before being intercepted by the GMRT, the 21-centimeter emission line had been stretched to 48 centimeters by the expansion of space, a phenomenon described as redshift of light.
The team used gravitational lensing to detect the signal, which originated from a distant star-forming galaxy called SDSSJ0826+5630. In gravitational lensing, light is magnified as it follows the curved space surrounding a massive object that sits between our telescopes and the original source, effectively acting like a giant lens.
“In this particular case, the presence of another massive body, another galaxy, distorts the signal between the target and the observer.” says astrophysicist Nirupam Royfrom the Indian Institute of Science.
“This effectively magnifies the signal by a factor of 30, allowing the telescope to pick it up.”
The results of this study give astronomers hope for more similar observations in the near future: the distances and lookback times that were previously taboo are now very well within reason. If the stars are right, that is.
Atomic hydrogen is formed when hot, ionized gas from a galaxy’s environment begins to fall toward the galaxy, cooling as it does so. Eventually it turns into molecular hydrogen and then into stars.
Being able to look back in time this far can teach us more about how our own galaxy first formed and lead astronomers to a better understanding of how the universe behaved when it was just beginning.
These latest findings will ‘open up exciting new possibilities in the near future for studying the cosmic evolution of neutral gas with existing and upcoming low-frequency radio telescopes,’ the researchers write in their published paper.
The research was published in Monthly Bulletins of the Royal Astronomical Society.
