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Starts With A Bang

Cosmic Cluster Collision Triggers Trio Of Active Galaxies

How to turn a galaxy on, once and for all.


“Speculating and predicting what lies beyond the boundary is fascinating. Finding out is even more fascinating.” –Wallace H. Tucker

When two galaxy clusters collide, the physics of the collision reveals where the normal matter is.

Visible light image of clusters Abell 3411 and 3412. Image credit: NAOJ/Subaru.

Rather than located in the galaxies themselves, the vast majority is found between the galaxies in the intra-cluster medium.

When the clusters collide, their mutual gravity causes an incredibly energetic cosmic smash-up, heating the gas to such high temperatures they emit X-rays.

X-ray emissions reveal the location of gas, and reveal an abundance that indicates that this is the majority of the clusters’ baryonic mass. Image credit: NASA/CXC/SAO/R. van Weeren et al.

Mysteriously, on the outskirts of the collision, intense radio emission can be found.

Radio emissions, found from much more energetic electrons, are found offset from the main X-ray emissions of the galaxy cluster collision. Image credit: NCRA/TIFR/GMRT.

The fact that these two signals are offset indicate that there’s another, secondary process at work.

The most energetic shock can be clearly seen around one of the galaxies, well-offset from the X-rays’ peak intensity. Image credit: X-ray: NASA/CXC/SAO/R. van Weeren et al; Optical: NAOJ/Subaru; Radio: NCRA/TIFR/GMRT.

A closer inspection reveals that the shockwaves from the colliding cluster gas is actually activating the supermassive black holes at the centers of three independent galaxies.

The supermassive black holes each exhibit jets and weak shocks, but only weak shocks are required to boost the jettisoned electrons by an additional factor of 1,000,000 in energy, creating this radio emission.

A multiwavelength, annotated view shows the supermassive black holes and jets that have been activated by the collision. Image credit: X-ray: NASA/CXC/SAO/R. van Weeren et al; Optical: NAOJ/Subaru; Radio: NCRA/TIFR/GMRT.

The giant structure of shocks is two million light years across: about the Milky Way-Andromeda distance.

A close-up of the three active galaxies as revealed in this energetic cosmic smash-up. Image credit: X-ray: NASA/CXC/SAO/R. van Weeren et al; Optical: NAOJ/Subaru; Radio: NCRA/TIFR/GMRT.

A combination of low-frequency radio arrays and a new X-ray telescope, ESA’s Athena, will reveal the full mechanism.

The proposed Athena X-ray observatory will provide critical answers that current X-ray observatories, like Chandra and XMM-Newton, cannot. Image credit: ESA / Athena Collaboration.

Other galaxies may yet activate/deactivate as the collision continues to evolve.


Mostly Mute Monday tells the story of a cosmic phenomenon or object in visuals, video and no more than 200 words.

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