Last updated June 26, 2019 at 12:47 pm
Two galaxy clusters have been discovered on the verge of collision, unleashing a monstrous 100-million degree shockwave.
Multi-wavelength view of galaxy clusters 1E2216 and 1E2215, which appear to come into first contact ahead of merging. Credit: NASA/CXC (X-rays); SDSS (optical); GMRT (radio); Liyi Gu et al. 2019
Two massive galaxy clusters have been discovered just before the point of collision, giving astronomers the best seats in the universe to watch the early stages of the cataclysmic event.
And in those first few moments as the galaxies approach each other they’ve seen massive shockwaves with temperatures up to 100-million degrees exploding from the collision.
That makes the shockwave around 17,000 times hotter than the surface of the Sun.
It is the first time clusters this close to smashing into each other have been seen. These collisions and mergers are one of the keys to understanding the structure of the universe, say the international team of researchers, including from Perth’s International Centre for Radio Astronomy Research.
Galaxy clusters on verge of collision
Clusters of galaxies are the largest known objects bound by gravity. Consisting of hundreds of galaxies that each contain hundreds of billions of stars, they’re surrounded by a halo of hot gas. Ever since the Big Bang, these objects have been growing by colliding and merging with each other.
The clusters, 1E2216 and 1E2215, are located over one billion light years away from the Earth. For billions of years they have been slowly drawn towards each other by gravity.
While astronomers have observed galaxy clusters mid-collision and post-collision, the early stages have remained elusive. Being able to see a collision from the very start will let astronomers test their theoretical models against an actual merger.
It is similar to seeing a raindrop that just touches the water surface in a photograph of a pond.
In particular, the researchers are expecting to see massive shockwaves spreading perpendicular to the axis of collision in the very first moments of collision.
Shocks during galaxy cluster merger. Credit: Courtesy of H. Akamatsu/SRON
“X-ray and radio images of these clusters show the first clear evidence for this type of merger shock”, says Liyi Gu, who led the research at RIKEN in Japan.
“The shock created a hot belt region of 100-million-degree gas between the clusters, which is expected to extend up to, or even go beyond the boundary of the giant clusters. Therefore, the observed shock has a huge impact on the evolution of galaxy clusters and large-scale structures.”
Temperature distribution of merging galaxy clusters IE2216 and IE2215. The colour scale ranges from 14 million °C (black) to 70 million °C (blue) to 80 million °C (red) to over 90 million °C (yellow). Credit: ESA/XMM-Newton; GMRT; Liyi Gu et al. 2019
Collecting snapshots to build a complete model of galaxy collisions
Spotting the impending collision required a huge amount of data. The team used three X-Ray satellites (ESA’s XMM-Newton, NASA’s Chandra, and JAXA’s Suzaku) combined with two ground-based radio telescopes (the Low-Frequency Array in Europe, and the Giant Metrewave Radio Telescope in India).
The team will continue to collect “snapshots” of the collision as it happens, allowing them to build a complete model of how galaxy clusters merge for the first time.
“This will help us to complete our understanding of the role of merger shocks in the formation of the largest structures in the Universe,” says Huib Intema from the ICRAR team who found the cluster.
With diameters of a few million light years, these galaxy cluster collisions can take about a billion years to complete. After the dust has settled, the two colliding clusters will have merged into one bigger cluster.
The research is published in Nature Astronomy.
