Friday, 12 May 2017

Yellow eyes and a fifty-tonne truck

The universe is all but a static place. As inconceivably vast as the distances between celestial objects may seem to us tiny humans, what are a couple of million lightyears when you've got billions of years of time? Even the great galaxies, entities as large as hundreds of thousands of lightyears across and containing billions to even trillions of stars may face calamities similar to a meteorite hitting the Earth. I've already talked about interacting galaxies many times before. Sometimes they're zooming past each other like Formula One cars going through a bend, such as this example. Sometimes they're merely bound by gravity such as the enormous Virgo Supercluster. In extreme cases they may even crash into each other, merge or be left completely deformed. Also the Andromeda Galaxy will eventually crash into our Milky Way. 

But there are also slightly less dramatic situations in which two galaxies simply hover close by and slowly devour each other. This seems to be the case with the two galaxies on my sketch: NGC4435 (right) and NGC4438 (left), which are currently only 100.000 lightyears apart. In comparison, Andromeda is 2,5 million lightyears away from us. Well, hovering is not exactly the correct term. They have come very close to one another many millions of years ago and have literally ripped each other apart in the process, but certainly not at the same speed as NGC672 and IC1727 in the example I linked to above. They're more in a sort of orbit at the heart of the Virgo Cluster, in an area we call "Markarian's Chain". This is a large chain of bright galaxies within this cluster, which is already a stunning sight in binoculars. 

NGC4435 seems to be completely stripped of its spiral arms, whereas the somewhat larger NGC4438's still trying to hold on to most of its matter. Its nucleus is highly distorted and in stead of spiral arms it shows long, irregular trails of stars and gas. Given the relatively slow orbit speed and consequently limited tidal pull between the two, scientists have been looking for other explanations why these two are in such a bad way. The most likely answer is M86, a gigantic lenticular galaxy not far away. Recently, filaments of ionised gas have been discovered between this giant (much like M87) and NGC4438. It's not only M86's size that's squeezing the two little ones, but also its incredible speed. M86's one of the few galaxies in the supercluster that's headed towards us in stead of away from us and it's doing it at the respectable speed of 244km/s. That doesn't seem like much as such but since most of the galaxies in the cluster are flying in the opposite direction with speeds well over 1.000km/s the movement of M86 becomes much more significant. As big as it is, M86's being stretched out by ram pressure. Imagine what's happening to your hair when you're doing 100mph in a convertible car. Now imagine that you're standing by the side of the road and a fifty-tonne truck zooms past at 100mph. That's what NGC4435 and NGC4438 are experiencing right now!

In popular culture, these two galaxies are referred to as the "Eyes Galaxies" for obvious reasons. Since there's not much of them left apart from their nuclei containing mostly older, yellow-orangy stars, these eyes are basically... yellow. 


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