Location matters most for the special galaxies at the hearts of galaxy clusters. These giant elliptical galaxies have gone by many names over the years, from cD galaxies to brightest cluster galaxies, but no matter what you call them, these systems do not behave like other elliptical galaxies. 

For instance, in Astro 101, students are taught that elliptical galaxies are red and dead — meaning they are filled with old red stars and are considered dead because they no longer have star formation. Central galaxies, it turns out, can be quite a bit different. 

In a new paper in Astronomy & Astrophysics with first author Bianca-Iulia Ciocan, researchers discuss the central galaxy in the massive MACS 1931.8-2635 galaxy cluster. This galaxy is roughly ten times the size of our Milky Way and is anything but dead; it is churning out nearly a hundred solar masses of stars per year. For comparison, our galaxy churns out a couple of new stars a year.  

This star formation is made possible by the infall of material from the surrounding intracluster medium and from the disrupted tails of material that signal galaxy mergers or collisions have taken place. Due to its distance, we can’t make out all the individual stars in the galaxy, but their combined light indicates 80% of the galaxy’s mass formed more than six billion years ago, and the observed star formation today is a new phase of star formation.

A new and beautiful phase of star formation.

More Information

Phys.org article

“The VLT-MUSE and ALMA view of the MACS 1931.8-2635 brightest cluster galaxy,” B.I. Ciocan et al., to be published in Astronomy & Astrophysics (preprint on arxiv.org)