The Sunyaev-Zeldovich effect in the Spiderweb protocluster

This animation shows how photons — particles of light — interact with the hot gas in the distant protocluster around the Spiderweb galaxy. 

Photons from the cosmic microwave background — the relic light from the Big Bang — are depicted as yellow-red streaks of light that traverse space in random directions. The galaxies are embedded in a massive cloud of plasma, with free electrons moving fast within it. 

The photons from the cosmic microwave background interact with the electrons in the hot gas, gaining a bit of energy as they do so. As a result, their wavelength or “colour” changes slightly, shown here as blue lines. This is called the Sunyaev-Zeldovich effect, and astronomers have used it to study the distribution of the hot gas within the Spiderweb protocluster, using the Atacama Large Millimeter/submillimeter Array (ALMA). The measured distribution of the hot gas is shown at the end of the animation as a blue cloud overlaid over the background field of galaxies.