A Love Note from Outer Space

Zoe Parker

The radio signal received is emitted by atomic hydrogen when its single electron undergoes a spin flip transition and emits a photon at a wavelength of 21cm. This wavelength is found around young stars, and has many uses in astronomy, most commonly as a tracer for probing the universe. This is not the first radio signal received by scientists on Earth, but the special interest around this particular signal is due to the fact that it has been received from the furthest galaxy yet.

This signal could therefore change the way we learn about the early universe. The signal was detected by scientists in India, using their Giant Metrewave Radio telescope and a technique called gravitational lensing. Large objects can warp the spacetime around itself, effectively bending light at different wavelengths ever so slightly

However, gravitational lensing acts to amplify the signal and change the wave’s direction form, its original straight-line course. This is a natural phenomenon that allows us to see deeper into the universe than we otherwise would have. Waves cannot maintain their initial energy without this amplification, as the expansion of the universe causes them to ‘redshift’ (an increase in wavelength and subsequent decrease in frequency and photon energy).

It is thought that a nearby galaxy acted to amplify the signal by almost 30x its original. The signal was emitted by a galaxy known as SDSSJ0826+5630, located 8.8 billion years away. This galaxy is older than our own (the ‘milky way’) by 0.1 billion years.

In astronomy, looking upwards is the same as looking back into the past when we look at the farthest objects. Because the universe is expanding homogeneously in every direction equally, it must therefore have expanded from something to begin with; a singularity where all the matter was in one single confined space. Receiving this signal from a galaxy so far away is therefore the equivalent of looking back 8.8 billion years. Not only is this the furthest we’ve ever had a radio signal from, but it has also provided details about the early universe, in particular young galaxy formation. Researchers have found that it has twice the mass of its visible stars, which could be yet another piece of proof for dark matter with further research. Work like this has enabled a new way of studying the early universe, enabling scientists to get a step closer to solving the mystery of its formation.