MACS J1206

Galaxy Cluster Reveals Stronger Concentration of Dark Matter than Predicted

This Hubble Space Telescope image shows the massive galaxy cluster MACS J1206. Embedded within the cluster are the distorted images of distant background galaxies, seen as arcs and smeared features. These distortions are caused by the amount of dark matter in the cluster, whose gravity bends and magnifies the light from faraway galaxies. This effect, called gravitational lensing, allows astronomers to study remote galaxies that would otherwise be too faint to see.

Astronomers measured the amount of gravitational lensing in the cluster to produce a detailed map of the cluster's distribution of dark matter. This elusive substance is the invisible glue that keeps stars bound together inside a galaxy and makes up the bulk of the universe's matter. Galaxy clusters are the largest repository of dark matter in the universe.

In addition to the dark matter smoothly distributed within the cluster, astronomers found that an expectedly large amount of it is concentrated in individual cluster galaxies. These concentrations produced gravitational lensing effects that are 10 times stronger than theory predicts.

Several of these galaxies are sufficiently massive and dense to also distort and magnify faraway sources. The galaxies in the three pullouts represent examples of such effects. In the snapshots at upper right and bottom, two distant, blue galaxies are lensed by the foreground redder cluster galaxies, forming rings and multiple images of the remote objects. The red blobs around the galaxy at upper left denote emission from clouds of hydrogen in a single distant source. The source, seen four times because of lensing, may be a faint galaxy. These blobs were detected by the Multi-Unit Spectroscopic Explorer (MUSE) at the European Southern Observatory's Very Large Telescope (VLT) in Chile. The blobs do not appear in the Hubble images.

MACS J1206 is part of the Cluster Lensing And Supernova survey with Hubble (CLASH) program and is one of three galaxy clusters the researchers studied with Hubble and the VLT.

The researchers suggest that this mismatch is either some physical ingredient that is missing in how the computer simulations are created or in astronomers' understanding of the nature of dark matter that shapes the formation and evolution of cluster galaxies.

The Hubble image is a combination of visible- and infrared-light observations taken in 2011 by the Advanced Camera for Surveys and Wide Field Camera 3.

Credits

NASA, ESA, P. Natarajan (Yale University), G. Caminha (University of Groningen), M. Meneghetti (INAF-Observatory of Astrophysics and Space Science of Bologna), and the CLASH-VLT/Zooming teams
Acknowledgement: NASA, ESA, M. Postman (STScI), and the CLASH team