Pictures of the week must be Hubble’s latest release which you could call a crash course in the phenomenon of colliding galaxies.
The space telescope team have isssued a collection of 59 new colour images of these vast star cities running into each other to mark the 18th anniverary of Hubble’s launch.
They show a fascinating array of intricate structures as the galaxies interact, and tidal effects change the forms of their wisps and loops.
Contrary to what one might imagine, galactic collisions do not result in enormous explosions. They are not like a cosmic car crash. The reason is the vast distance between the stars which means that they simply pass each other as they sail through space in different directions.
The Hubble team note that interacting galaxies are found throughout the universe and can trigger bursts of star formation or even form new galaxies.
Such mergers, which were more common in the early universe than today, are thought to be one of the main driving forces for cosmic evolution. They switch on quasars, spark frenetic star births and prompt explosive stellar deaths.
Even apparently isolated galaxies will show signs in their internal structure that they have experienced one or more mergers in their past, say the astronomers. The merging galaxies captured in the released series of images are snapshots of different moments in the long interaction process.
Our own Milky Way contains the debris of the many smaller galaxies it has encountered and devoured in the past, and it is currently absorbing the Sagittarius dwarf elliptical galaxy. In turn, it looks as if our Milky Way will be absorbed by its giant neighbour, the Andromeda galaxy.
They are rushing towards each other at a staggering 500,000 km per hour – yet the collision will still not happen until around two billion years time, forming a new super galaxy which wags have dubbed Milkomeda.
Picture: NASA, ESA and the Hubble Heritage Team.