Phoenix cluster is cooling faster than expected

With increasingly advanced data, Michael McDonald and colleagues study a galaxy cluster bursting with new stars.

Fernanda Ferreira | School of Science
November 20, 2019

From the very beginning, it was clear that the Phoenix cluster was different from other galaxy clusters. When assistant professor of physics Michael McDonald looked at the first image of the Phoenix cluster taken by the Magellan Telescope in Chile, he saw an unexpected hazy circle of blue.

Galaxy clusters like Phoenix are, as the name suggests, a cluster of hundreds or even thousands of galaxies held together by gravity and permeated with dark matter and hot gas. When the hot gas cools, star formation happens. Given the amount of hot gas in galaxy clusters, astronomers expected to find large nurseries of young stars. Instead, they found older stars, which usually glow red, and a black hole at the center of the cluster pumping out energy, keeping the gas too hot for explosive star formation.

Most clusters appear the same when observed through a telescope. “When we look at the center of clusters, we see galaxies that are spherical or football-shaped and red,” says McDonald, who is also a researcher at the MIT Kavli Institute for Astrophysics and Space Research (MKI).

The blue light McDonald saw in Phoenix, however, is a telltale sign of a young star, which burns hotter and brighter. Confirming that the blue light was the result of new star formation would take advances in the quality of data and access to three powerful telescopes to figure out what makes the Phoenix cluster unique.