Hubble spots two galaxies on collision course

This latest picture from the NASA/ESA Hubble Space Telescope shows two galaxies on the course of collision - NGC 3558 in the lower left, and LEDA 83465 in the upper right. Both galaxies lie roughly 450 million light-years from Earth, the two galaxies are practically on top of one another - separated by a distance of roughly 150,000 light years.

The larger galaxy pictured here is an elliptical galaxy while the smaller galaxy is a barred spiral. Both belong to Abell 1185 - a crowded and chaotic galaxy cluster that lies approximately 400 million light-years away from Earth and spans one million light-years across.

Notably, NGC 3558 is both an elliptical galaxy and a low-ionisation nuclear emission-line region (LINER). LINERs are a particular type of galactic nucleus that emit light at certain wavelengths, suggesting that many of the atoms and molecules within these galactic cores have either been weakly ionised or not ionised at all.

"Ionisation is the process by which atoms or molecules lose or gain electrons. In galaxies, it is driven by a variety of processes — from shockwaves travelling through galaxies, to radiation from massive stars or from hot gas in accretion discs. In the case of LINERs, this means that many of the atoms and molecules within the galaxies have lost either a single electron or have retained all their electrons. The mechanism that drives this weak ionisation in LINERs such as NGC 3558 is still debated amongst astronomers," ESA explained in a post.

🌀💥🌀Two galaxies on collision course are the highlight of our ESA/Hubble Picture of the Week. NGC 3558 in the lower left lies about 150 000 light years away from galaxy LEDA 83465 in the upper right. That might sound vast, but it isn't. 1/2 pic.twitter.com/k9KFvCC31j

— HUBBLE (@HUBBLE_space) October 9, 2023

Galactic collisions shape the structure and evolution of galaxies in cosmic timescales. The Hubble Space Telescope eagle view of the cosmos shows such galactic encounters were more common in the past when the universe was smaller.

According to NASA, our Milky Way galaxy is also destined for a head-on collision with its neighbouring Andromeda galaxy, which is predicted to happen four billion years from now. Currently, Andromeda is about 2.5 million light-years distant from the Milky Way galaxy.