Monday, 5 December 2016

The flying ghost galaxy

Those who've been following my blog have already been testimonies to many dramatic events that happen in the Universe around us. I've shown you the birth and the death of stars, supernova explosions and galaxies that have been ripped apart by unimaginably strong tidal forces. Today, I'd like to share a sketch of another incredible event: two galaxies that are crashing into each other!

NGC520, or popularly named the "flying ghost galaxy", is an object that's within reach of small telescopes under a dark sky. Right from first glance you'll notice that something's not quite right with it. It doesn't look like an ordinary galaxy at all, with a clear nucleus and spiral structure around it. A larger aperture telescope reveals the true nature of the cataclysm that started some 300 million years ago and that's now reached its most spectacular stage. Two nearby galaxies were attracted so much to one another by their mutual gravitational forces that they collided. However, you shouldn't think of this as the collision of two cars in a big fire ball. Given the enormous distances between the individual stars in a galaxy, it's highly unlikely that, when two galaxies meet, their stars will crash into each other. They'll simply fill the void and in the end the two galaxies will merge into a new and much bigger one. That being said, the tidal forces that these crashing galaxies generate, will seriously stir up the new entity and in turn this will lead to a burst of new star formation. 

Think of a galaxy as a cup of coffee with milk. Older galaxies that don't interact with others stop moving and become plain... the coffee being brown and uninteresting. Star formation comes to a halt. In younger galaxies - imagine these as coffee to which you've just added the milk - the gas clouds swirl and contract in the gravitational vortices, leading to the formation of many new stars. In the particular case of our flying ghost galaxy, the collision has added fresh milk and the gravitational pull is giving the whole a really good stir. Expect to see an explosion of new star births there!

The collision of galaxies is certainly not a unique event. Actually, in about 3,75 billion years the nearby Andromeda Galaxy is going to crash into ours! Our Sun will almost have reached the end of its life by then and honestly I don't think there will still be humans around to witness it, but as I explained, it won't be the end. It will be a new beginning.

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