Starship Asterisk*

X-ray: NASA/CXC/RIKEN/L. Gu et al; Radio: NCRA/TIFR/GMRT; Optical: SDSS

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For the first time, astronomers have found two giant clusters of galaxies that are just about to collide, as reported in a new press release by RIKEN. This observation is important in understanding the formation of structure in the Universe, sincelarge-scale structures—such as galaxies and clusters of galaxies—are thought to grow by collisions and mergers.

The composite image shows the separate galaxy clusters 1E2215 and 1E2216, located about 1.2 billion light years from Earth, captured as they enter a critical phase of merging. Chandra’s X-ray data (blue) have been combined with a radio image from the Giant Metrewave Radio Telescope in India (red). These images were then overlaid on an optical image from the Sloan Digital Sky Survey that shows galaxies and stars in the field of view.

The discovery of 1E2215 and 1E2216 at this stage of merging has enabled astronomers to test their computer simulations of these important collisions. This new result provides evidence of a shock wave that is generated early in the merging process and travels out away from the collision in a perpendicular direction. ...

• Nature Astronomy (online 24 Jun 2019) DOI: 10.1038/s41550-019-0798-8
• arXiv.org > astro-ph > arXiv:1906.10285 > 25 Jun 2019