Lucia McCallum (The Conversation) Tasmania

The scientists who precisely measure the position of Earth are in trouble. Their measurements are essential for the satellites we use for navigation, communication and Earth observation every day. Surprisingly, making measurements, using the science of geodesy, depends on tracking the locations of black holes in distant galaxies.

The problem is the scientists need to use specific frequency lanes on the radio spectrum highway to track those black holes. And with the rise of wifi, mobile phones and satellite int­ernet, travel on that highway is starting to look like a traffic jam.

Satellites and the services they provide have become essential for modern life. From precision navigation in our pockets to measuring climate change, running global supply chains and making power grids and online banking possible, our civilisation cannot function without its orbiting companions. To use satellites, we need to know exactly where they are at any given time. Precise satellite positioning relies on the so-called “global geodesy supply chain”.

This supply chain starts by establishing a reliable reference frame as a basis for all other measurements. As satellites are moving around Earth, Earth is constantly moving around the Sun, and the Sun is constantly moving through the galaxy, this reference frame needs to be carefully calibrated via some relatively fixed external objects. 

The best anchor points for the system are the black holes at the hearts of distant galaxies, which spew out streams of radiation as they devour stars and gas. The black holes are the most distant and stable objects we know. Using a technique, very long baseline interferometry, we can use a network of radio telescopes to lock onto the black hole signals and disentangle Earth’s own rotation and wobble in space from the satellites’ movement. 

We use radio telescopes as we want to detect the radio waves coming from the black holes. Radio waves pass through the atmosphere and we can receive them during day and night and in all weather conditions.