Record-breaking galaxy cluster confirms dark matter Universe
“These galaxies are among the most massive galaxies in the universe and are believed to have rapidly formed their stars a long time ago. However, how these galaxies formed and why have they stopped forming new stars remain mysteries.” -Tao Wang, lead author on this new study
There was once a time early on in the Universe where there were no stars, no galaxies and no clusters of galaxies at all. While stars and galaxies form very early on, after only tens or hundreds of millions of years, it takes billions of years for the first clusters to form. Yet even if we were to look back into the Universe’s past up to ten billion years, the clusters we see are already well-evolved and quiet.
The light from the “El Gordo” galaxy cluster, ACT-CL J0102-4915, comes to use from over 7 billion years in the past. It’s incredibly massive at over 3 quadrillion suns, but the giant ellipticals are already formed and are much quieter and full of older stars than a “new” cluster would indicate. Image credit: NASA, ESA, J. Jee (University of California, Davis), J. Hughes (Rutgers University), F. Menanteau (Rutgers University and University of Illinois, Urbana-Champaign), C. Sifon (Leiden Observatory), R. Mandelbum (Carnegie Mellon University), L. Barrientos (Universidad Catolica de Chile), and K. Ng (University of California, Davis).
We had never seen a set of galaxies fall in and actively form a cluster before. We’d never seen the protocluster/cluster transition before. And we’d never found one from when the Universe was between two and three billion years old: when our dark matter theory predicts the first great clusters ought to form. Until, that is, now.
An optical/infrared image of the center of CL J1001, from ESO’s UltraVISTA survey. The right panel shows a close-up view with the redshifts of galaxies labeled, and two galaxies containing actively growing black holes labeled as “AGN”. Image credit: Tao Wang.