Relics of Fireworks Past
More news today from the “huge things of the universe” department: a team of astronomers has discovered a gigantic shockwave emanating from a cluster of galaxies that is about 60 times the size of our Milky Way galaxy. (To put that into perspective, our home Galaxy is about 100,000 light years wide.) The shockwave, also called a ‘relic,’ occurred when two clusters of galaxies merged about 1 billion years ago, making a new cluster rather innocuously named Abell 3667. (George Abell was an ardent cataloguer of galaxy clusters – and he wrote the textbook I used for my introductory astronomy class 35 years ago!) You can see the image showing the shock waves (coloured orange) in the attached images, one of the galaxy cluster itself and a zoom-in on one of the shockwaves that shows the size of the Milky Way to scale. What fireworks that must have been! The image was actually obtained with the new MeerKAT radio telescope, of which HAA provided some important contributions, as part of a larger international Galaxy Cluster Legacy Survey. As with many low frequency images, the emission seen here was produced when electrons whiz around local magnetic fields, producing a low level glow called “synchrotron emission.” In this particular case, the electrons were likely part of the hot medium previously between the galaxies in each cluster that were forcibly ejected when the two clusters slammed into each other at high speed. Though the collision occurred many hundreds of millions of years ago, the ejecta are still moving very fast, about two and a half times the local speed of sound (i.e., Mach 2.5), producing the observed shock wave. Here’s a link to the press release from the South African Radio Astronomy Observatory (SARAO), which includes a third image of the shockwave where the orientation of the magnetic fields involved in the detected emission are shown. Also, here’s a link to the Astronomy & Astrophysics paper by the team who produced the spectacular image. It will be amazing to see how extensive this shockwave really is once the much more sensitive Square Kilometre Array gets a look at it in the years to come!
Abell 3667 with surrounding shockwaves. Credit: F. de Gasperin (SARAO)
Close-up of the northern shockwave of Abell 3667 with size of the MIlky Way to scale. Credit: F. de Gasperin (SARAO)