A large area of my research is focussed on a new technique for mapping the Universe’s structure across vast volumes, spanning millions of light-years. This technique uses radio telescopes to scan the sky and record the emission from neutral hydrogen gas. Neutral hydrogen, or HI (pronounced H-one), refers to a particular form of hydrogen where its negative and positive electric charges are balanced so it is ‘neutral’. HI is very abundant in galaxies so if we can detect neutral hydrogen, we can trace where large amounts of galaxies are in space. This technique, known as HI intensity mapping provides maps that tell us where the Universe has dense structure and where it has voids of empty space. This probe of large-scale cosmic structure is a crucial probe to answer fundamental questions about our Universe.
A quirk of hydrogen is that it spontaneously emits a photon at fixed energy, and therefore at a fixed wavelength which is 21cm. By conducting low angular resolution radio telescope surveys, we can scan large swathes of the sky for this 21cm signal. By measuring how the HI wavelength (or frequency) changes we can make a redshift measurement which we use for a distance estimation. This allows us to build 3-dimensional maps of our Universe.
[Credit: CAASTRO]
Steven Cunnington 