An Indian telescope, the Giant Meterwave Radio Telescope (GMRT), has just broken a distance record by detecting a radio signal from 8.8 billion years ago. What they have “seen” in this signal: hydrogen. This is the furthest direct detection of this element in space and time by any telescope.
Double the previous record.
Galaxies are bright objects that emit their energy at a multitude of frequencies in the electromagnetic spectrum. But not all of them are easy to spot. One reason is that the lower frequencies (the longer waves) carry less energy.
Until now, the detection of this type of frequencies was only possible at relatively short distances, since to the problem of the low energy with which these waves start, we must add the factor of the expansion of the universe. This expansion does not simply move the elements of the universe away from each other but enlarges the fabric of the universe itself, and thereby stretches the electromagnetic waves. It is the phenomenon known as redshift or redshift.
At 8.8 billion light-years this implies that the wave was multiplied by a factor of about 2.3, or a redshift of z ∼ 1.3. The previous record was found in light emitted 4.4 billion years ago (a redshift of z ∼ 0.376).
How far had this wave extended in its length? It had gone from 21 centimeters to 48. But the important fact is the first, 21 centimeters, a key distance in our universe. This wavelength, corresponding to 1420 MHz in the electromagnetic spectrum, is produced by a specific change in the state of hydrogen.
When a proton and an electron come together to create a hydrogen atom, their spins may or may not coincide in the new atom created. About 50% of hydrogen atoms are born in each state, but it so happens that the spin coincidence state creates a more energetic version of hydrogen.
The most energetic hydrogen atoms can decay to the lowest energetic state (although not the other way around), although this is an extremely rare change that takes an average of 10 million years to occur. When this jump happens, the atom releases a photon. A very particular one, since its wavelength is precisely 21 centimeters. It is this change in hydrogen atoms that the team has just detected in a galaxy billions of light-years from us.
Image of the signal captured by the GMRT telescope. Chakraborty & Roy/NCRA-TIFR/GMRT.
Hydrogen is, due to its simplicity, a ubiquitous element in the universe. However (or perhaps because of this) it is an element that can tell us a lot about its environment. Hydrogen begins to form, in the vicinity of galaxies. It is originally an atomic gas, hot and ionized, which gradually cools down and begins to unite into molecules, to later form clusters that end up giving rise to the formation of stars.
The finding has been published in the Monthly Notices of the Royal Astronomical Society. In the piece, the team of astronomers gives an account of how they were able to make the discovery. The key piece in this has been a galaxy in the middle, with the charismatic name of SDSSJ0826+5630.
“In this specific case, the signal is curved by the presence of another massive body, another galaxy, between the target and the observer,” explained one of the authors of the study, Nirupam Roy, in a press release. “This effectively results in magnifying the signal by a factor of 30, allowing the telescope to pick it up.”
A year of records.
What we thought we knew about the early universe is changing by leaps and bounds. In its first months of activity, the James Webb Space Telescope observed a significant number of very bright and complex galaxies whose presence and number puzzled astronomers.
The work of Webb and the GMRT shows a bright future for telescopes, increasingly sensitive tools capable of looking not only at what is happening around us but also beyond distance and time.
Thanks to this, we have an increasingly better idea of how stars and galaxies formed, but new telescopes can also help us find interesting aspects of the closest universe, bringing us closer to how the conditions for the appearance of life could have arisen, both on our planet as on others. In any case, having our eyes on the sky will undoubtedly give us a better image of what we can find beyond our own planet.
Imagen | McGill University