Shock wave from colliding galaxy clusters spans 60 Milky Ways

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The 2 red parts of this image are the edges of an enormous shock wave, extending for 6.5 million light-years. The bright white oval at the center consists of a cluster of galaxies, called Abell 3667. But the individual galaxies are too small to see individually at their distance of some 700 million light-years. As 2 galaxy clusters collided to form Abell 3667, shock waves emanated outward, creating the 2 red structures we see today. Image via Francesco de Gasperin/ SARAO.

Astronomers said in late February 2022, that they’ve obtained the most detailed view yet of a shock wave that extends across 6.5 million light-years of space. You’d need 60 Milky Way galaxies end-to-end – each one filled with hundreds of billions of stars – to equal the extent of these shock waves. The shock waves are on each side of the galaxy cluster Abell 3667, which lies more than 700 million light-years away from us. When the galaxy clusters that created this cluster collided, it produced shock waves. The astronomers said it’s one of the most energetic events that’s taken place in our universe since the Big Bang. Wow!

The international team of scientists published their study on January 31, 2022, in the peer-reviewed journal Astronomy and Astrophysics.

Galaxy cluster Abell 3667

This massive event involved two separate galaxy clusters that joined to form Abell 3667. The clusters collided more than a billion years ago. The scientists used the MeerKAT radio telescope in South Africa to get a better view of the galaxy cluster and its shock waves. Alexis Finoguenov of the University of Helsinki, who participated in the study, said:

The presence of the shocks in Abell 3667 is detected using sharp changes in the properties of the hot gas, traced by its X-ray emission.

Lead author Francesco de Gasperin of the University of Hamburg and INAF said:

These structures are full of surprises and much more complex than what we initially thought.

A closeup of the larger shock wave shows the complex filamentary structure. Most of the galaxies you can see in this image are not part of Abell 3667 but either in front of or behind it. To get an idea of just how large the shock waves are, see the inset at the top right of the Milky Way for scale. Image via Francesco de Gasperin/ SARAO.

Seeing magnetic fields in the shock wave

The radio wave data allows scientists to see how the particles move across the magnetic fields. The scientists can thus trace the magnetic field lines, which are the regions where particles are excited to high speeds. De Gasperin said:

The shock waves act as giant particle accelerators that accelerate electrons to speeds close to the speed of light. When these fast electrons cross a magnetic field, they emit the radio waves that we see. The shocks are threaded by an intricate pattern of bright filaments that trace the location of giant magnetic field lines and the regions where electrons are accelerated.

The shock wave races across the galaxy cluster at speeds of 3.3 million miles an hour (1,500 km/s). Or, as the press release said:

This means that the shock front would cross the entire Earth in the time needed to read this sentence.

Irregular orangish arc with bright points of light on black background.
This closer view of one of the shock waves shows the orientation of the magnetic field lines. Image via Francesco de Gasperin/ SARAO.

Bottom line: A team of international astronomers have gotten the best look yet at a shock wave from galaxy clusters colliding to form Abell 3667.

Reference/Journal DOI:10.1051/0004-6361/202142658 Astronomy and Astrophysics

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